Rick's Free Auto Repair Advice » Diagnostics

No Start – Jeep

Rick — Sat, 17 Sep 2011 15:15:02 +0000

Several people have posted questions on help forums about their Jeeps not starting. Here are some of the top reasons. Since there are several Jeep models and different designs over the years, this is just a summary. If you want detailed information on YOUR system, buy a subscription to AlldataDIY or eautorepair.net from the links below

You turn the key and lights come on, but starter does not start cranking

Ignition Switch

Jeep is experiencing cracked/split ignition switch/lock cylinder

Jeep ignition switch

related failures. In some cases a plastic tab breaks off the switch and allows it to flex/twist or move slightly. In others, the lock cylinder housing cracks. The switch moves enough to supply power to the lighting contacts, but not enough to power up the starter. Check the switch. If the lock cylinder housing is cracked, you’ll need a new steering column. Start checking the junk yards.

Linkage between lock cylinder and ignition switch

Linkage from lock cylinder to ignition switch breaks

Neutral safety switch

The PCM must see that the vehicle is in Park or Neutral. Some

Neutral safety switch

of these safety switches are know failure points. The switch is located on top of the valve body and is called the transmission range selector (TRS). Try starting the vehicle in neutral rather than park. If that does it, the TRS is either out of adjustment or corroded. Plug the connector apart and look for green corrosion. If you find it, treat it with Stabilant 22

Security Light is on

There’s a problem with the SKIM security module

No Check Engine Light

The Check Engine Light should ALWAYS come on

Powertrain Control Module (PCM/ECM)

when you first turn the key. It’s doing a “bulb check.” If you’ve checked the bulb and it’s ok, you’ve got connection or PCM problems.

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.

If you just need information for a single repair and want to save money,eautorepair offers a lower price 1-week subscription for only $11.99. Or, if you’ll be working on this vehicle in the future, you can buy a 1-year subscription (Alldatadiy.com for $26.99, or eautorepair.net $29.99)

Alldatadiy.com

eautorepair.net

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

Intermittent problems on GM vehicles

Rick — Thu, 08 Sep 2011 21:23:07 +0000

GM vehicles from the mid ’90′s to the present are known for faulty ignition switches. The problems are almost always intermittent. Intermittent starting, dying while driving, A/C to start blowing warm air or for the blower fan to stop (depending on which GM model we’re talking about), along with an ABS light. In fact, any time you see erratic or intermittent problems that could be electtrical in nature on a GM vehicle, you should immediately suspect the ignition switch. Always test the igntion switch during an intermittent problem to see if the switch is providing power (use a meter).Or, wiggle the wires going to the switch. GM techs replace so many of these that it’s almost automatic for them to head there first

In the case of the A/C the problem is usually the ignition switch heating up and not providing power to the A/C clutch and the ABS computer. If you want to diagnose the problem, buy a wiring diagram for your vehicle form eautorepair.net or alldata.com (there are way to many GM models to list their wiring diagrams here) and test for power at the switched terminals when the problem happens. Or, just replace the ignition switch.

Alldatadiy.com

eautorepair.net

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

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.

Alldatadiy.com

eautorepair.net

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

A/C doesn’t work and ABS light on

Rick — Thu, 01 Sep 2011 17:53:39 +0000

GM vehicles are known for faulty ignition switches. The problems are almost always intermittent. One common symptom is for the A/C to start blowing warm air or for the blower fan to stop (depending on which GM model we’re talking about), along with an ABS light. The problem is usually the ignition switch heating up and not providing power to the A/C clutch and the ABS computer. If you want to diagnose the problem, buy a wiring diagram for your vehicle form eautorepair.net or alldata.com (there are way to many GM models to list their wiring diagrams here) and test for power at the switched terminals when the problem happens. Or, just replace the ignition switch.

Alldatadiy.com

eautorepair.net

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

Lights dim, warning lights flash, car stalls

Rick — Sat, 20 Aug 2011 16:44:32 +0000

Happened to you? That’s the sign of a dead battery. Normal battery voltage should be between 12.25 and 12.75 volts. You need that much to start a vehicle. But if the alternator isn’t working and the battery starts to drain, voltage falls. Once it goes below 10-volts, strange electrical behavior starts. In fact, the computer will shut off completely at 9.6-volts.

So before you start looking for shorts or bad ground wires, charge the battery and then check the alternator. Click here to see how to do that.

Alldatadiy.com

eautorepair.net

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

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.

Alldatadiy.com

eautorepair.net

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

Cannot shift into or out of Park

Rick — Tue, 28 Dec 2010 20:51:41 +0000

As a safety precaution auto makers require you to step on the brake pedal before shifting into or out of PARK. Stepping on the brake activates a small solenoid in the steering column (or in the console on floor shifter models). The solenoid retracts a locking pin, allowing the shifter to move.

When the shift interlock solenoid fails, you cannot move the shifter. The cause can be a burned out fuse or a bad solenoid. If the fuse is burned, suspect either a shorted solenoid OR chafing in the wiring harness. However, if the fuse is good and the solenoid operates, then check for spilled soda or hot chocolate that’s worked its way down the steering column and gummed up the works.

Every manufacturer provides a mechanical release mechanism for emergencies where the shift interlock fails. The mechanical bypass is described in your owner’s manual.

Alldatadiy.com

eautorepair.net

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

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.

Alldatadiy.com

eautorepair.net

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

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:

Alldatadiy.com

eautorepair.net

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

Where to get wiring diagrams and repair information

Rick — Sun, 25 Apr 2010 21:22:38 +0000

I volunteer on a LOT of auto repair forums and I constantly see people asking for free wiring diagrams and step-by-step repair instructions. The first thing you need to know about online wiring diagrams is that there is NEVER a single wiring diagram for your car. When I need a diagram, I have to enter the year, make, model, and OPTIONS into the first page of the program. Why? Because a wiring diagram for power doors locks on a 2001 Ford Taurus WITH a security system is different than the diagram for the exact same vehicle WITHOUT a security system. I could go on and on, but the bottom line is that if you don’t key in all that information, you’ll get the wrong diagram. So when online posters just as for a wiring diagram for their vehicle, their chances of getting the right diagram are, you guessed it, ZIP. Nadda. The same applies to step-by-step repair information—it’s different for vehicles depending on what equipment you have and which engine/transmission combination is in the vehicle.

Next, you should know that there’s really no such thing as a free wiring diagram or free shop manual. The cheap manuals (Haynes, Chilton, etc) have really lousy diagrams (in my opinion), which is why you see so many posts that say, “I have a Haynes manual but need a wiring diagram for….” The car companies are charging for all repair information these days and it’s not cheap. So in order to get your hands on good reliable information, you simply have to bite the bullet and pay for it. Here are your options.

1. eautorepair.net – This site is run by Mitchell on Demand, which is used by the pros. They redraw all the factory wiring diagrams so they are MUCH easier to read. Really, I’d rather use their diagrams than any factory manual. Their repair instructions are good too. The downside to this service is their lack of body repair information. You cannot get any door panel removal instructions or any interior door repair steps. The same goes for instrument panel removal. The upside is that their service is very accessible for DIY’ers. You can buy a 1-week subscription for $12. They also sell a 1-month and 1-year subscription.

2. Alldata – This site is like the eautorepair site except that they DO include some body repair information. They have diagrams that show how to remove door panels and some dash panels. Their wiring diagrams are all FACTORY diagrams. If you know how to read them, great. If not, it can be quite a challenge for the average DIYer. They offer a 1-year subscription for $27.

3. Factory shop manuals – There’s no comparison here. These are the best manuals out there. They have the most diagrams and the best instructions. They also include in-depth articles on how the systems work. That can really help you when it comes to diagnosing a problem. The downside? The cost. Click here to find the site for your make. http://www.oem1stop.com/

3. Public library – That’s right, you forgot about them, didn’t you. Many public libraries subscribe to online repair services. If you have a library card you can use their computers and print out the repair instructions or diagrams for a small fee. The downside is that most libraries require you to access the service from inside the library—meaning, you can’t get it from home.

4. Ebay – If you sign on to ebaymotors, you’ll find tons of factory DVDs for cheap prices. Often these are bootleg copies. But if you’re concerned about whether they’re selling a legit copy, ask the seller.

Here’s the bottom line, and there is NO way around it—if you want reliable information, you’re going to have to pay for it. You would not believe the number of emails I get from people who have wasted days trying to fix their cars with the wrong wiring diagram, torque specs, or incorrect or missing repair steps. If only they had spend a few bucks on a subscription, they could have read the latest technical service bulletin warning them NOT to replace the entire ABS control module simply because the ground wire needed cleaning. Yes, it happens that often.

Alldatadiy.com

eautorepair.net

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