Rick's Free Auto Repair Advice » By Trouble Code

Code readers and scan tools

Rick — Mon, 05 Sep 2011 17:02:15 +0000

If you wanted to do your own car repairs in the “old days” you need specialized tools. You had to own a timing light and a distributor wrench at the very minimum. For diagnostic tools you needed a tach/dwell meter. In others words, you had to put some “skin” in the game if you wanted to save shop labor.

Today, I hear DIYers whine every time their check engine light goes off and they have to get the codes scanned. My take on this is “GROW UP!!” If you want to do your own car repairs, you need a basic set of tools. And today, that means you have to own either a code reader or a scan tool. Don’t want to make the investment? Fine, then take it to a shop and pay them $100 a pop to hook up their scan tool.

Have I convinced you to buy your own scan tool yet? If so, let’s take a look at the offerings. Rather than review tools from every manufacturer, I’ll give you my bias right up front. SPX is a major tool manufacturer. They’ve been making specialty tools for most (GM and FORD all specify SPX’s tools) car makers for decades. When electronics came into play, Owatonna Tool Company (OTC) was the first to build scan tools for independent shops. OTC is owned by SPX. Next, SPX bought Actron, which used to be known as KalEquip (they made my tach/dwell meter back in the ‘60’s). They also bought AutoXRay. What I’m getting at is that SPX not only has direct connections to the car makers, but they own the top scan tool companies in the world. That’s why I tell readers to buy their tools.

What’s the difference between a code reader and a scan tool?

A code reader just reads the trouble code. That’s it. They’re cheap (less than $50), but they don’t do much for you. Once you get the code, you’re one step closer to solving the problem, but you’re still missing a LOT of critical information. If you’re a real cheapskate and only want to buy a code reader, here’s what to look for.

The cheapest code readers don’t have batteries. That means you can scan for the code and read the trouble code only as long as it’s plugged into the computer. Once you have the code, you’ll have to go to your home computer to look up the code definition. What a pain. But then again, you are a cheapskate. Oh, by the way, once you unplug it, the information is gone. So you’d better bring a pen and paper with you. But if you spend a bit more, the code reader will have a battery that maintains the code information in memory. Dig a little deeper and you’ll get a code reader with a back-lit screen. Dig deeper still and you’ll get a code reader that’ll spit out the code definitions right on the screen. And many of those higher end readers are update-able (as manufacturers develop new codes).

Or, get a real diagnostic tool

Let’s not kid each other—a code reader is a toy. Sure, it’ll give you the code, but that’s it. If you’re like most DIY’ers, you’ll get the code definition and replace every part mentioned in the trouble code. So if the code says oxygen sensor lean, you’ll replace the oxygen sensor. The parts manufacturer’s love people like you. Every year tens of thousands of perfectly good 02 sensors are replaced just because the trouble code contained the words oxygen sensor. Engine computers are smart, but they’re not that smart. They may tell you that the oxygen sensor is reporting a lean condition. You assume that means the sensor is bad. Most often it’s telling the truth, the exhaust stream really IS lean. What would cause that? Yup, a vacuum leak. But you won’t get to that point until you’re replaced an $80 sensor and wind up with another check engine light. How to get around that? Buy a scan tool that gives you live data and then learn how to interpret the data.

Here’s how live data helps you

When an engine computer sees a lean condition in the exhaust, the first thing it does is add more fuel to the mixture. This is called Fuel Trim. The computer tracks how much fuel it adds or subtracts. It can add or subtract up to 25%. So, if you’re seeing a lean or rich trouble code, the first thing you should do is look at the live fuel trim data. If the computer is adding fuel, that’s an indication of a vacuum leak. If it’s subtracting fuel, that’s an indication of a leaking fuel injector or a fuel pressure problem. Do you see where this is going? A scan tool gives you the data to actually diagnose the problem. THAT’s why you should pony up the money and buy a scan tool with live data. Yes, they’re expensive. But trust me, you’ll waste far more than that by replacing perfectly good parts because you were too cheap to buy a real diagnostic tool in the first place. Let’s see, you replaced both O2 sensors ($160) and the check engine light is still on. And the root problem was caused by a .25 vacuum hose? You could have owned a scan tool for close to that same money.

Buying Tips

I’m listing many models of Actron and AutoXray tools here. Do not buy them based on price. Read their specs and MAKE SURE the one you like actually works with your vehicle. Many of the less expensive scan tools do NOT read manufacturer-specific codes–especially on European vehicles. You’ll have to spend upwards of $300-$500 to get that capability. Finally, none of these inexpensive tools will read ABS, AIRBAG, Chassis, or Universal codes. To get that capability, you’ll have to spend about $2,000. Want that? Great. Buy an OTC Genisys scan tool.

For more information on this repair or any others for your vehicle, buy an online subscription to either Alldatadiy.com or eautorepair.net. Click on this link to compare the two services: Compare Alldata and Eautorepair.

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Check Engine Light is On

Rick — Mon, 04 Jul 2011 21:18:36 +0000

I volunteer in many different automotive forums and I constantly see people ask what could be the cause of a Check Engine light. The current system that’s in place to monitor engine performance and emissions is called On-Board Diagnostics version II (OBDII). The system is capable of setting up to 1,800 different trouble codes. That doesn’t even include manufacturer-specific codes that can be used to tell if there’s a problem with a body control computer or chassis system. With 1,800 possibilities, there’s simply no way anybody can get any kind of answer when they ask, “Why did my Check Engine light come on?”

The ONLY way to start the diagnostics to find out why the check engine light came on is to plug in a code reading tool and poll the computer. Once a trouble code sets and lights the light, that code is stored in computer memory. The code reader or scan tool (there’s a difference between the two) polls the computer memory and pulls up the trouble code. Some units decipher the code and tell you what it means in plain English, while others just pop up the code.

Once you have the code, you can do two things: 1) Fix the problem, or 2) Clear the code. Now, I get asked a lot “How to I clear the code or turn off the light.” I’ve got news for you, you’re not fooling anybody if you think you can turn off the light and then take your car or truck in for an emissions inspection. Because the computer will tell the inspector that you’ve just cleared the codes. The inspector will tell you to come back and have the car checked again after the computer has reset its readiness monitors. (See drive cycles to understand what you have to do after clearing codes to be able to take and emissions test).

And, you CANNOT reset ABS or SRS (airbag) lights. You have to fix the problem.

Finally, be aware that the computer tracks how many times you’ve started the car with the Check Engine light on. So, if you’re under warranty or driving a leased vehicle and think that you can dodge the charges for engine damage by claiming that the “light just came on,” think again. They can tell when the light first came on.

How to check codes

1) Take it to an auto parts store that checks codes for free. Most major retail auto parts stores (like Autozone, Advance Auto, O’Reilly) will scan your computer for free. But beware, their parts guys are NOT technicians. So if the trouble code translates into “Oxygen sensor lean,” I guarantee you the parts guy will sell you a new oxygen sensor. Do you need one? Well, what if the exhaust stream really IS lean and the oxygen sensor is telling the truth? $80 down the drain. Remember, parts stores are in business to sell parts. Don’t rely on them to diagnose problems.

2) Buy your own code reader or scan tool
In the early days of OBDII, code readers and scan tools cost a fortune and only professional technicians could afford them. But today you can buy a code reader for $40. All right, I can hear you whining. But before you go into a full pity-party, remember that “in the old days” we had to buy special tools to work on cars. Remember tach/dwell meters for setting “points” in the distributor? Or that timing light you had to use to set timing? How about those distributor wrenches that you only used once every 3 years? So get over it—you’re going to have to spend money on a new tool.

What’s the difference between a code reader and a scan tool?

A code reader reads codes—period. It doesn’t tap into the vehicle’s computer to display “live data.” Knowing the code if helpful, but it’s just a start towards diagnosing the root cause. The majority of Do It Yourselfers who buy code readers end up guessing at the problem and replace a LOT of parts unnecessarily. So you saved yourself a bunch of money on the code reader only to throw far more money into parts you didn’t need.

A scan tool, on the other hand, displays the same data that the computer receives from it’s sensors. If we follow the oxygen sensor example from above, the first thing I’d check in live data is the value for “Short-term Fuel Trim.” When the computer sees a lean condition, it figures it calculated the wrong air/fuel mixture. To correct the problem, it adds more fuel. That additional fuel is referred to as Fuel Trim and the value runs from 0 to 25%. So, in this case, if I were to see a fuel trim of 25% along with an oxygen sensor “lean” code, I would know that I had a huge vacuum leak. In other words, too much air is getting into the engine, the computer is trying to compensate for it and it has max’ed out it’s ability to correct it, and the oxygen sensor is still seeing a lean condition. Remember I told you a parts guy would sell you an oxygen sensor? Well, in this case, I’d be looking for a broken vacuum hose or a bad intake manifold gasket. There, you just save almost enough money on this single repair to justify owning a scan tool.

What else can you read on a scan tool?

Engine RPM, engine coolant temperature, radiator fan operation, transmission operation, barometric pressure, MAF, MAP, VSS, TPS sensor values –getting the picture? You can literally “look” into the computer and get the data.

So buy a scan tool and read up on how to use it and interpret the values.

I’ve listed some of the more popular models of code readers and scan tools below. But read the fine print on the model you want to buy. MAKE SURE IT WORKS ON YOUR VEHICLE. Also, these inexpensive scan tools only pull “P” codes. They will not read ABS, Airbag, or other manufacturer-specific codes. If you want to read all those codes, you’ll need to pony up about $4,000 for a professional model with all the software.

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P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 P0309 P0310 P0311 P0312

Rick — Thu, 04 Nov 2010 04:42:18 +0000

P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 P0309 P0310 P0311 P0312

Pinpointing cylinder misfire codes

People ask me about misfire codes after they’ve replaced all the spark plug wires, coil, and plugs and they still have the code. Here’s a quick explanation of how a pro would attack the problem.

First, if you’re getting a P0300 Random/Multiple Cylinder Misfire Detected code, that would indicate a universal problem that applies to all cylinders. In that case, start by checking fuel supply issues like poor fuel pressure caused by a bad pump, restricted fuel filter, or a defective fuel pressure regulator. If all those check out, look for a major vacuum leak or EGR valve leak. EGR is recalculating exhaust gas back into the intake manifold. If it isn’t operating properly and letting too much exhaust in, it will lean out the air fuel mixture to all cylinders. So check those things first. If you’re still seeing multiple misfire codes, it’s time to examine the timing chain or belt to see if the valve train is out of time with the crankshaft. That would cause poor valve sealing. Of course, in an abused engine, or one with a ton of miles, there’s always the possibility of poor cylinder compression or leaking valves. But that usually doesn’t cause misfires on all cylinders. So let’s take a look at individual cylinder misfire codes.

The thing to keep in mind about cylinder misfire codes is that the computer really doesn’t know whether the spark made it to the spark plug or not. All it knows is that a cylinder or isn’t contributing it’s fair share of power. How does the computer detect this? Easy. It looks at the crankshaft position sensor and calculates its rate of rotation. It knows when it fired the coil for a particular cylinder and it knows when it fired the fuel injector. So it looks to make sure that the crankshaft position sensor reflects that cylinder’s contribution to power. If the computer notices a SLOWDOWN in the RATE of the crankshaft rotation, it calculates backwards to see which cylinder isn’t doing it’s job.

Like I said earlier, the computer doesn’t know whether the spark actually occurred, so it’s mistake to always assume that a misfire means bad ignition. A misfire can certainly be caused by faulty ignition. But it can also be caused by poor fuel mixture—too much air or too little gas. Let’s look at the possibilities.

In a “too-lean” mixture situation, there’s too little gas present to make a good long fire. The computer could be commanding a lean mixture due to a dirty MAF sensor, a bad oxygen sensor, or a leaking fuel injector. In those cases, the computer is trying to throttle back the gas to correct for what it saw previously as a too rich mixture. Or, the lean mixture could be caused by the proper amount of gas AND a vacuum leak. So, the computer thinks it got the mixture right, but the vacuum leak screwed things up. Whatever the cause of the too-lean mixture, the result is always the same—there’s too little gas (in relation to the amount of air) and the flame goes out too soon due to lack of fuel. Yup, the computer calls that a misfire.

In a too-rich situation, the flame STILLS goes out to soon, only this time it’s flames out because there’s not oxygen to keep the fire going. Yup, that’s a misfire too.

So you have to think in broader terms than just ignition when it comes to misfires.

Ask yourself these questions:

Is the cylinder getting fuel (fuel pressure good)?
Is the injector clogged (too little gas)?
Is there a vacuum leak near that cylinder?
Is the EGR valve leaking?
Is the cylinder getting enough fuel flow (restricted fuel filter—may have pressure, but not enough volume)
Is an injector leaking (causing a rich misfire)
Is the compression good? (valves seating, timing right)

This is where a scan tool with live data can really help. By reading the “fuel trim” numbers, you can tell whether the computer is trying to compensate for a lean or rich condition. Unfortunately, the scan tools that provide that kind of information are pricey. Plan on spending at least $400 for a pro scan tool.

Hope that helps.

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P0400 Exhaust Gas Recirculation Flow Malfunction Nissan

Rick — Tue, 14 Sep 2010 23:57:57 +0000

Owners of 1999 Nissan Altima 2.4L and 2000 Nissan Frontier 2.4L vehicle may encounter a P0400 trouble code with a check engine light. Owners may also notice an engine stall at idle when the vehicle is warm. Before you start replacing parts, learn how the system works and test each component according to this procedure.
Start by checking the rubber hose that goes to the bottom of the EGR back pressure transducer. The transducer measures the amount of “backpressure” in the exhaust system to determine if the EGR valve is operating properly. Because exhaust gas is so hot, it can sometimes burn the hose. A burned hose will cause improper EGR operation. If you find any cracks, holes, or burn marks, replace the hose.
Next, tee in a vacuum gauge to the EGR valve vacuum supply and drive the vehicle until warm. Monitor the gauge to make sure the EGR valve is receiving vacuum. It should be between 2 to 4-in. to be within range. If it is, then move to the next step. If not, refer to the EGR vacuum solenoid check below.
If you have vacuum, then connect a voltmeter to the blue/yellow wire on the EGR temp sensor. Drive the vehicle (with the vacuum gauge still attached) and look for sensor voltage drops to less than 1v. That indicates proper EGR operation. The sensor checks for a temp increase once the EGR opens and exhaust flows. If the sensor voltage drops, then you’re getting EGR flow. If the sensor doesn’t see hot gas, the PCM will set the trouble code.
If you’re not getting vacuum at the EGR valve, check the hoses running between the EGR valve and the EGR solenoid, and the solenoid and the intake manifold. The EGR solenoid receives grounding “pulses” from the PCM. The duration of the pulses determines how long the solenoid remains open, allowing vacuum to flow to the EGR valve. That’s how most car makers regulate the opening and closing of vacuum operated EGR valves.

Get a new exhaust gas temperature sensor here:

Get a new EGR valve here:

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P0128 and temperature gauge dead – GM vehicles

Rick — Sat, 27 Mar 2010 00:07:38 +0000

If you get a P0128 diagnostic trouble code with your OBDII scan tool AND the temperature gauge is dead, head right for the thermostat When a thermostat goes bad on a GM vehicle, the PCM sets a P0128 trouble code and commands the cooling fans to run and disables the temperature gauge. Don’t waste time trying to fix the gauge. First, replace the thermostat. If the gauge still doesn’t work, then you can start diagnosing that problem after you’ve cleared the P0128 code.

Find a thermostat for your vehicle here

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Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

P0507 Idle Control System RPM Higher Than Expected

Rick — Sun, 21 Mar 2010 16:47:22 +0000

On vehicles with “drive by wire” technology, the computer determines idle speed and commands a stepper motor on the throttle body to open and close the throttle plate. If it sees an RPM that is higher than the commanded RPM, it sets this code.

P0500, U1262 codes on Ford F-150 5.4L

Rick — Sun, 21 Mar 2010 07:24:17 +0000

If you have a Ford F-150 with the 5.4L engine and have a flashing ABS light and a speedometer that stops working intermittently, or a temperature gauge that goes to HOT intermittently, read this article.

Ford has had significant problems with its ignition coils. Occasionally a coil can fail in such a way that it generates a large voltage spike that confuse the computer. That can set off all kinds of weird behavior. If you have the vehicle scanned, chances are you will NOT find any misfire codes, nor will you find any ABS codes. The P0500 code is for loss of vehicle speed sensor input and a U1262 coded indicates a loss of communication between the Hybrid Electronic Cluster and PCM.

Since no misfires codes come up in the OBDII scan, you’ll need a high end scanner capable of reading the raw (uninterpreted) data known as Mode $06. That mode stores raw misfire data and analyzes it until it meets the parameters to set a trouble code. Viewing Mode $06 is the only way to detect which coil is misfiring and spiking. Or, you can start replacing coils until you find the culprit. Just don’t start replacing ABS components or instrument clusters.

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use

Engine flush

Firing order, cylinder layout, finding #1 cylinder

MAF or MAP sensor

Oxygen sensors, How they work, How to change, How to test

PassLock or Passkey

Thermostat issues

Transmission flush

Serpentine belt diagrams

Window issues, power window motor, replace window regulator, glass adhesive

P0125 Insufficient Coolant Temperature For Closed Loop Fuel Control

Rick — Fri, 19 Feb 2010 19:22:23 +0000

P0125 Insufficient Coolant Temperature For Closed Loop Fuel Control

You need to determine whether the engine coolant temperature sensor is telling the truth and the engine really isn’t coming up to operating temperature, or whether the sensor is bad. Many DIYers rush to replace the sensor. And yes, they do go bad. But not nearly as often as the thermostat.
So start your diagnostics by checking coolant level. If it’s low, fill it. Then, using an infra-red thermometer, check the temp around the thermostat housing. At operating temperature, it should be about 195°. If it doesn’t reach that point, you’ve got a thermostat that’s stuck open. A thermostat and gasket is cheaper than a temp sensor.

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use

Engine flush

Firing order, cylinder layout, finding #1 cylinder

MAF or MAP sensor

Oxygen sensors, How they work, How to change, How to test

PassLock or Passkey

Thermostat issues

Transmission flush

Serpentine belt diagrams

Window issues, power window motor, replace window regulator, glass adhesive

P0507 Trouble Code on Nissan Altima

Rick — Wed, 27 Jan 2010 16:51:15 +0000

The computer sets this code when it see an idle speed 200RPM or more above the commanded RPM set by the computer. The system may appear as a high idle or a surging idle. That can occur right after someone cleans the throttle body. This procedure applies to 2002-2005 Nissan Alimas.

This system eliminates the traditional throttle cable that used to run from the accelerator pedal to the throttle body. Instead, it uses and electronic accelerator pedal that sends a varying signal to the PCM. The PCM then commands a motor located at the throttle body to open and close the throttle plate. Over time, the throttle plate can develop carbon buildup that restricts the flow of air into the engine at idle. The PCM compensates for this by opening the throttle plate more. But once the throttle body is cleaned, the excess air increases the idle speed.

There are two ways to force a “relearn” procedure to get the PCM back to a good setting for the throttle plate. One involves a genuine Nissan Consult II scan tool, which most independent repair shops do not have. The other is a manual procedure.

Here’s how the manual procedure works. It’s a multi-step process.

First, perform an accelerator pedal released position learn procedure.
With the accelerator pedal fully released, turn the key to the ON position and wait at least two seconds. Then turn the key off and wait 10 seconds. Turn the key back to ON and wait at least two seconds. Then turn the key off and wait 10 seconds.

Next, perform the throttle valve closed position learning procedure.
With the accelerator pedal fully released, turn the key to ON than off. Wait 10 seconds. Listen for the sound of the throttle motor to verify that the throttle plate is moving.

Then you have to perform the idle air volume learning procedure.

The charging system must be in working order. To check, start the engine and use a digital multimeter to test the voltage at the battery. Drive the vehicle at least 15 minutes to warm up the engine and transmission to fully warm. With the engine running, battery voltage must be at least 12.9 volts. The transmission must be in park or neutral. All electrical accessories must be turned OFF. Center the steering wheel and make sure the wheels are pointing straight ahead.

If the idle speed is high, turn off the engine and disconnect two fuel injectors to bring the idle speed down. The PCM cannot relearn if the idle speed is too high.

Have a watch with a sweep second hand or a stop watch for the next steps. The timing MUST BE EXACT.

With the accelerator pedal fully released, turn the key to ON for exactly 3 seconds. Then fully depress the accelerator pedal and fully release it five times within 5 seconds. Wait exactly 7 seconds and fully depress the accelerator pedal and KEEP it depressed. After about 10 seconds the Check Engine light will start blinking. If it does not start blinking after waiting 20 seconds, turn the key OFF and wait at least 10 seconds. Then repeat the procedure from the very start. You may have to repeat this beginning procedure a few times until you get the Check Engine light to start blinking.

Once the Check Engine light starts blinking, let it continue to blink until it comes on steady. That usually takes another 10 seconds. Once it stays on steady, you must fully release the accelerator pedal within 3 seconds and start the engine. Let the engine idle. The relearn actually starts once the engine is running. The proceeding steps were just to prepare the PCM for the relearn procedure.

Let the engine idle for 20 seconds. If the relearn was successful, the RPM will drop. Turn off the engine and reconnect the fuel injectors you disconnected earlier. Then restart the engine to see if idle is normal.

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use

Engine flush

Firing order, cylinder layout, finding #1 cylinder

MAF or MAP sensor

Oxygen sensors, How they work, How to change, How to test

PassLock or Passkey

Thermostat issues

Transmission flush

Serpentine belt diagrams

Window issues, power window motor, replace window regulator, glass adhesive

P0400 EGR Malfunction Nissan Altima

Rick — Fri, 01 Jan 2010 23:20:43 +0000

Nissan’s EGR system is similar to other manufacturers. The PCM pulses a solenoid to regulate how much vacuum the EGR valve gets. That determines how far the valve opens. To determine if the valve is actually opening, the PCM looks to the EGR backpressure transducer and the EGR temperature sensor.

If you get the P0400 Exhaust Gas Recirculation Flow Malfunction code, first check to make sure the hose to the bottom of the EGR valve is intact and not burned. If that checks out, “T” a vacuum gauge into the line to the EGR valve and drive the vehicle. If you see vacuum, that will confirm that the PCM is commanding it and that the solenoid is providing it. The vacuum gauge should read between 2”-4” of vacuum. If you don’t see vacuum, check the hoses and the solenoid for malfunction.

Next, connect a voltmeter to the blue/yellow wire on the temperature sensor. With the engine running, apply vacuum and watch the voltage reading. The engine should run rough at idle and the reading should drop to less than 1 volt very quickly. If you don’t see that drop and you’ve already confirmed that the EGR is operating properly, replace the temperature sensor.

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use