Rick's Free Auto Repair Advice » GMC Trucks

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.

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)

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

P0332, Circuit Low Input (Bank 2) on GM products

Rick — Tue, 06 Sep 2011 04:10:36 +0000

Also P0335 and P0340

If you think you should replace the knock sensor after getting this code, think again. This is a perfect example of where a sensor can be telling the truth and the root cause of the problem is somewhere else. Here’s the scoop. Most late model engine use variable valve timing to change the opening and closing timing of the valves. The device that actually changes the valve timing is called the cam phaser (yeah, like on Star Treck). Some cam phasers use oil pressure to rotate the camshaft slightly to change the timing. That’s great when it’s working well. But if you’ve changed your own oil and used a viscosity that’s different from the manufacturer’s recommendations, you can screw up the phaser. For example, some people don’t believe the manufacturer’s recommendation to use 5W-30. So they change their oil with 10W-30. The slightly thicker oil can cause the phaser to respond more slowly to computer commands. And when the cam is out of phase from the commanded position, you can get pre-ignition, or pinging. Yup, if you used this oil and now have this trouble code, point your finger right at yourself.

The same holds true if you think you can get away with not changing your oil on time. Think sludge buildup isn’t a problem? Well guess what, sludge in a cam phaser can also cause trouble codes.

If you’re getting these codes and think it might be caused by oil, change your oil and filter and drive the vehicle first. Perhaps the clean oil can clear out the passages.

Here are a few other things that can cause this trouble code:

Check the electrical connector on the cam phaser. If you see oily buildup, disconnect the connector and check inside. Oil can sometimes seep into the connector and that would give false readings.

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!.

Instrument Cluster Doesn’t Work

Rick — Mon, 08 Aug 2011 02:18:30 +0000

GM has issued a Technical Service Bulletin (1549143) for 2001-05 Chevrolet Silverado and GMC Sierras equipped with the Allison LCT1000 transmission. The instrument cluster can be erratic, drop out, become inoperative, or result in a trouble code of P0721, C0237, P0500, C0055. In addition, the transmission may exhibit trouble shifting. Also, the ABS light can illuminate. The problem may be caused by a bad vehicle speed sensor (VSS) or a damaged reluctor wheel.
The Allison tranmission sends a speed signal to the transmission control module. The signal is AC voltage of 34Hz at 1MPH. The transmission control module converts the AC signal to a digital waveform and sends it to the powertrain control module. That speed signal is then fed to the instrument cluster, radio, ABS brake module and the cruise control. So a bad VSS can be the source of all these problems. I could tell you how to test the sensor, but you’d need an expensive Fluke multimeter. It’s cheaper to replace the sensor.

Alldatadiy.com

eautorepair.net

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

GM vehicles with B0071 or B0081 trouble codes.

Rick — Mon, 18 Jul 2011 02:02:52 +0000

If you own one of the vehicles listed below and see a lit SRS (supplemental restraint system) light on your dash, you may have one or both of these trouble codes: B0071 or B0081. Both codes relate to a problem in the Sensing and Diagnostics module. Don’t start replacing air bad components like the clock spring or the module. The problem is most likely the result of a defective seat belt tensioner sensor located in the passenger side seat belt buckle. Contact the dealer for the updated sensor and install it. That should clear the code.

2005-07 Buick Terrazas
2005-09 Chevrolet Uplander, Pontiac Montana
2006-07 Chevrolet Impala
2006-10 Buick Lucerne, Cadillac DTS, Chevrolet HHR, Hummer H3s
2207-10 Cadillac Escalade, ESZ and EXT, Chevrolet Avalanche, Cobalt, Silverado, Suburban, Tahoe, GMC Canyon, Sierra, Yukon, Yukon Denali, Yukon XL, Pontiac G5
2009-10 Hummer H3Ts

Alldatadiy.com

eautorepair.net

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

Electronic Fan Clutch Failures on Rainier, Trailblazer, S10, Isuzu Ascender, Oldmobile Bravada, Saab 9-7X, and S15 GMC Envoy

Rick — Tue, 15 Mar 2011 05:16:03 +0000

Electronic Fan Clutch Failures on Rainier, Trailblazer, S10, Isuzu Ascender, Oldmobile Bravada, Saab 9-7X, and S15 GMC Envoy

The electronic fan clutch in the above vehicles experiences almost a 100% failure rate. The purpose of the fan is to reduce drag on the engine at highway speeds where “ram-air” is enough to cool the radiator. At highway speeds, a fully engaged clutch actually spins slower than the air coming through the radiator. So it reduces gas mileage. Thermostatically controlled viscous fan clutches have been around for decades to solve the problem. Those clutches are made from two halves with concentric circles that mesh. The gaps are filled with a silicone fluid. As the engine temperature rises, a thermostatically controlled valve closes off the flow of fluid and the concentric circles lock together under the pressure, transmitting the full torque to the fan blade. However, at higher speeds, the rush of aid past the thermostatic coil opens the valve, allowing the circles to disengage. At that point the fan blade “free-wheels” with the ram air.
Starting in 2002 GM replace the thermostatic coil with an electronically controlled “duty cycle” solenoid and an RPM indicator. The powertrain control module monitors engine and road speed and calculates how fast the fast should turn to properly cool the engine. To adjust fluid pressure in the clutch, the PCM pulses the solenoid on and off in short burst. This is called “duty-cycle.” For example, GM may divide each second into to pulses. If the PCM commands the solenoid on five times every other 1/10 of a second, the fan has a 50% duty cycle. The see how well things are working, the PCM compares the actual fan RPM to the RPM it expected when it calculated duty cycle. If the two speeds don’t match, the PCM makes further adjustments.
When the electronic fan clutches fail, they can lock on full time or free-wheel full time. Free-wheeling causes overheating and lock up reduces gas mileage and causes a howling noise at highway speeds.
To replace the fan clutch you’ll have to remove the fan shroud and fan blade. Mark the orientation of the fan blade before unbolting it completely. It must go back on in the same way. Then unbolt the old electronic fan clutch and swap it out.
The list price on a new fan clutch from the dealer is around $234. But Dorman Products makes an aftermarket replacement for $130. This is a new (not rebuilt part).

Alldatadiy.com

eautorepair.net

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

ABS light on GM vehicles

Rick — Fri, 16 Apr 2010 17:17:57 +0000

GM has issued a TSB #04-05-025-002A covering the following vehicles:
2004 Buick Rainier
2002-04 Cadillac Escalade, Escalade EXT
2003-04 Chevrolet Silverado
2000-04 Chevrolet Suburban, Tahoe
2003-04 Chevrolet Avalanche, Trailblazer
2003-04 Chevrolet SSR
1999-04 GMC Sierra
2000-04 GMC Yukon, Yukon Denali, Yukon XL
2002-04 GMC Envoy
2004 GMC Envoy XUV
2002-2004 Oldsmobile Bravada

The problem shows up as a glowing ABS light and trouble coded C0265, C0201, U1041 and a loss of communication with the brake module (EBCM). The TSB warns dealers NOT to replace the EBCM. The problem is a bad ground. Refer to a wiring diagram to find the grounding location for your vehicle. Then clean the ground area and spray it with rubberized undercoating.

For midsized utility vehicles, find the location of ground #304
For Chevrolet SSR, find the location for ground #400
For full-size trucks and utilities, find the location for ground #110

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

No instrument panel, HVAC controls dead, blower motor dead, flashers dead, GM vehicles

Rick — Sun, 21 Mar 2010 07:36:08 +0000

Bad ground TSB for GM vehicles

GM has issued a TSB #04-08-45-010 covering 2004-05 Buick Rainier, 2002-05 Chevrolet Trailblazer, 2002-05 GMC Envoy, and 2002-03 Oldsmobile Bravada.

The bad ground connection can cause the instrument panel lights to be inoperative, HVAC controls inoperative, blower motor inoperative, radio inoperative, flashers inoperative, and transfer case controls inoperative. The cause has been found to be a poor ground at a splice area G201 located on the right side of the front console area.

To fix the problem, you must remove the center floor console. Then remove the 4 screws that hold the instrument panel lower closeout carpet panel to the instrument panel. Next, remove the panel.

Remove the splice pack bolt. If the bolt is corroded, clean it with a wire brush. Remove any carpet that was trapped during assembly. Clean the ground surface with emery cloth. Reassemble the panel and console.

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

Performance Chip? GM Revokes Warranty on Chipped Vehicles

Rick — Fri, 18 Dec 2009 23:16:46 +0000

GM issued a technical service bulleting (TSB) #09-06-04—026 regarding revocation of warranty coverage on any GM vehicle in which the factory calibrations (software) has been removed or altered. The TSB applies to ALL GM gasoline passenger cars and trucks from 2006- present.

It’s important to note that GM is seeing enough damaged engines and transmissions to make this announcement. Here’s a direct quote from the TSB:

“When alteration to the GM-released engine or transmission control calibrations occurs, it subjects powertrain and driveline components (engine , transmission, transfer case, driveshaft and rear axle) to stresses that were not tested by General Motors. It is because of these unknown stresses, and the potential to alter reliability, durability and emissions performance, that GM has adopted a policy to cancel any remaining warranty coverage to the powertrain and driveline components whenever the presence of a non-GM (aftermarket) calibration is confirmed – even if the non-GM control module calibration is subsequently removed.”

The TSB goes on to instruct the dealers on how to determine if the factory calibrations have been altered or removed. So don’t think you change restore the factory programming and tear into the dealer when they refuse to cover your warranty claim. They CAN tell what you’ve done.

So, if you’re planning on “chipping” your vehicle (which I do NOT recommend), be aware that you’re on your own and that the likelihood of damage to the engine and transmission increases dramatically.

Also, remember this: engine design is always a compromise between power, responsiveness, emissions, and fuel economy. You cannot change one variable without changing all the others. So, while chipping may increase power in one range of operation, you will pay for it in other areas. There’s no free lunch, despite what the chipmakers want you to believe.

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

Door locks window problems on Chevrolet Colorado and GMC Canyon pickups

Rick — Fri, 18 Dec 2009 17:17:36 +0000

GM has issued a technical service bulletin (TSB) #PIT3164B to discuss a problem with door locks and power windows on 2004-09 Chevrolet Colorado pickups and 2004-09 GMC Canyon Pickups. The problem shows up as inoperative or intermittent door locks or power window operation. In many cases, fuse #42 in the underhood fuse box may blow. GM has identified two scenarios that would blow this fuse:

1) The fuse blows when opening/closing power windows and using the door locks at the same time.

2) When closing all the windows at the same time.

Here’s what GM recommends. First, inspect the wiring harness in each door and look for chafing at the door hinge area. Repair any chafing your find. GM rerouting the wiring harness for all vehicles built after May 31, 2004.

If you don’t find any chafing, GM’s TSB tells dealers to tell customers that this is a “Design Characteristic” and that no attempts should be make to fix the problem. In other words, there is no problem. The advice is to tell the customer not to operate multiple windows at the same time and not to operate a window and a door lock at the same time. Each of these situations result in maximum current draw and will blow the fuse.

Find a new door lock actuator for your vehicle here

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