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Chevy Silverado and GMC Sierra Electrical and Computer Questions



  • if the rattling cat is on the passenger side it may be your problem. if the cat is not burning off unburned fuel the post cat oxygen sensor will read a rich condition and the computer will deliver considerably less fuel to that bank of cylinders causing misfires.
  • Thanks for your response. I haven't had any trouble with the misfiring for a week. The rattling at the cat area has stopped, actually right before the misfiring started. I did get a diagnostic check run on the truck after the intake gasket was replaced and it misfired again and nothing came up, cats are good at the current 77,000 miles. I thot for sure the cats were bad, something was rattling under there and I never could find out what it was, everything was tight. Its purring like a kitten now, I'll keep on trucking. Thanks again.
  • kodak1kodak1 Posts: 1
    just joined this forum hope this helps you it was my problem my battery would always run down on my 06 4x4 it ended up being my windshield wiper motor shorting against the body try unplugging it for a few days. later
  • denhamdenham Posts: 76
    Service Engine Light with Code 440 emission fault, can not seem to find the problem.
    Have checked the wires and plugs, gas cap,etc. The canister is ok, but not sure how to check the purge solenoid? Anyone who has had this problem or idea I can use!
    With the code cleared you can start and drive maybe three times before the service engine light comes back on.
  • shaneoshaneo Posts: 2
    here is your solution unplug the battery for 3mins just enough to reset your truck and pllug back the battery and turn your ignition back on a wham bye bye service engine light.....keep me posted
  • obyoneobyone Posts: 8,054

    The EVAP LARGE LEAK TEST is based on applying vacuum to the EVAP system and monitoring the rate of vacuum decay. The Powertrain Control Module (PCM) uses the input from the Fuel Tank Pressure (FTP) sensor in order to determine the rate of vacuum decay. At an appropriate time, the PCM turns the EVAP canister purge valve ON (open) and the EVAP canister vent valve ON (closed). This allows the engine to draw a vacuum on the system. At a calibrated time or vacuum level, the PCM turns the purge valve OFF (closed), and tests the system vacuum. If the system is unable to achieve the calibrated vacuum level, the PCM will set DTC P0440.


    •DTCs P0107. P0108, P0110, P0112, P0113, P0115, P0117, P0118, P0121, P0122, P0123, P0125, P0443, P0449, P0452, P0453, P1106, P1107, P1111, P1112, P1114, P1115, P1121 or P1122 are not set.
    •The system voltage is between 10-18 volts .
    •The startup (ECT) engine coolant temperature is between than 4-30°C (39-86°F) , but the start up ECT is not more than 8°C (14°F) more than the startup IAT temperature.
    •The startup (IAT) intake air temperature is between than 4-30°C (39-86°F) , but the start up IAT is not more than 3°C (7°F) more than the startup ECT temperature.
    •The fuel tank level is between 15-85 percent .
    •The Barometric Pressure (BARO) is more than 75 kPa .
    •The Vehicle Speed Sensor (VSS) is less than 75 mph .
    The EVAP system is not able to achieve or maintain vacuum during the diagnostic test.


    •The control module illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
    •The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

    •The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    •A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    •A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    •Use a scan tool in order to clear the MIL and the DTC.

    •Use the EVAP pressure/purge diagnostic station in order to pressurize the EVAP system to aid in locating intermittent leaks.
    •Move all EVAP components while testing with the Ultrasonic Leak Detector.
    •A temporary blockage in the EVAP canister purge valve, purge pipe or EVAP canister could cause an intermittent condition. To repair a blockage in the EVAP system refer to Evaporative Emission (EVAP) System Cleaning. See: Emission Control Systems\Evaporative Emissions System\Service and Repair
  • denhamdenham Posts: 76
    Yes undo the battery will clear the code and the light will go out, but not fix the problem. The gas tank must build up pressure and most often it is the gas cap weak from use and you get the check engine light. This was my problem and I would say that anyone who has check engine light what any type auto they should first replace the gas cap as it could very well be the problem at little cost.
  • 03 1500 silverado..left turn signal will stop blinking when i put foot on brake pedal
  • my gadges go up and down and my batt. light comes on for a couple second and the gadges go crazy, rpm,speedomoder, oil,water temp, alt gadges go crazy and then quit working. does any body knows the problem please let me know. I change the alt. still not working. ray.
  • azjasazjas Posts: 6
    It is the ignition harness causing you all the problems.
    Replace it -
  • We just bought a 2003 Silverado 1500 Z71, today we were leaving a store and all the lights on the instrument panel lit up (all of them at the same time) and the headlights dimmed for a second, then everthing was fine, went to another store and when I shut off the truck the electric door locks did not unlock, so I tried to start the truck and it was dead, nothing would come on, after a few attempts to start it, it just suddenly started, so we decided to go straight home, a few seconds after we pulled out the lights all came on again, Ive tried starting it a few times since with no problem, has anyone had a similar problem or any suggestions for me? i dont want to be left stranded somewhere.
  • huff, I had this problem with my 99' silverado 4.8,i replaced the fuel press. regulater & solved the problem.Got the part @ napa 84$,hope this is it yourself job. tcbusa
  • I have a 2006 silverado with 2 codes 1 is p0102 mass airflow sensor low circuit frequency and p0449 vent solenoid control circuit how can i fix these 2 problems
  • Short story long, I had to jump my truck in the dark and like a big idiot I crossed the cables on the battery for about 30 seconds. Noticed the black cable on the positive post glowing. Quckly switched them and the truck started ok and made it home. I know, very stupid. Since then I have been getting a rough idle at stop signs where it feels like it might stall and the battery gage begins jumping from about 11 to 16 or so and it normally sits right at 14. I am also getting behavior where the radio will change stations or jump to new cd tracks if I hit one of the seat location buttons in the drivers side door and back to the original when I hit the other. The seat changes position to the correct position like normal. I have also had the radio turn off and reset itself back to 12:00. I have checked all of the fuses that I could find in the dash and in the box by the battery and they all seem good. Any thoughts on what I might have fried and how I can fix this?
  • my passenger side door is "dead". I cant roll up or lock that door and the remote lock is not working either. It also stalls out while driving once and a while. Checked all the fuses?????? any help is appreciated
  • :sick: Hate to say but it sounds like your door is unplugged maybe on the inside.
    Your going to need to pull the door panel and check the connection.
    Good luck
  • I have a 2003 GMC 1500 (5.3L V8) with 107,000 miles, which has been acting up recently. About a month ago, on a dark rainy night, I took the truck out to run some errands and noticed that while having the headlights, wipers, and windshield defroster on the truck seem to strain at Idle or when I came to a stop (strain= headlights would dim, the engine/electrical system would cycle, then return to normal). When I was driving no issues. After this happened a few times, I turned the defroster off and it strained again but no issues after that.

    The next day, early am (still dark) I had to ran into a similar situation, but the truck then stalled. I promptly replaced the alternator, thinking that it was faulty due to the mileage and age of the truck. Still had issues, many close stalls when I would come to a light but no stalls.

    After a few more issues, and some wondering if I would get stranded somewhere, I put a volt meter on the truck. Read 14V when it was idling, but when the headlights and defroster were turned on the volts dropped to 8 or 9. So, I figured it may be the battery and replaced that with a "red top" Optima battery.

    Even after all that, I am noticing some of the same issues with running the windshield defroster at night and the headlights. The truck strains, but does not stall and the volt meter will return to 14V on the dash after it cycles. I have noticed lately that this is also happening with the rear window defroster (even if it is on and the windshield defroster is off).

    Anyone have any ideas? I want to point the final finger at the heater motor/heating system but am not sure. Could this also be a relay issue? Anybody hear of this happening to others?

    Only other issues to date are, the instrument panel has a light burned out on the speedometer. The 4WD switches stopped working one day (months ago), but came back and are fully functional again. Last year I replaced all the plugs and wires as a DIY tune up and have had no issues with them. Truck came back to life when I did that..

    The truck runs like a champ all the other time. I still love my truck.
  • I had problems with my charging system on my 2003 2500 when it was about 2.5 yrs old. Voltage took wild swings high and low. Dealer replaced wire harness to alternator 'for proper continuity' per bulletin /PI. 73170D. That did the trick. 2 months later though, they did need to replace the 'intermittent' alternator due to undercharging. I did need to replace the alternator again this year ( 7.5 yrs old, 55,000 miles).
  • So Im kinda going crazy and hoping someone can help!!! A day ago my voltage on my display was acting up and the battery message was displayed. It went away so i thought it was not big deal. Later on it proceeded to do the same thing only this time the voltage did not come back up to 14...instead the battery completely drained and killed all the electrical.

    I have since replaced the alteranator and the battery thinking this would solve everything and it ofcourse did not. The battery message is still displayed. It doesnt constantly stay on...comes on for about 5-10 seconds and then goes away. I have had both the new battery and the alternator checked and the computer says that they are fine. Anyone have an idea of what is up with the message?
  • have a 2003 2500HD with the Allison Transmission.

    While driving this morning, the truck seemed to stutter and wanted to stop running. The truck did continue to run, but the engine light immediately came on.

    I used a Actron CP9135 diagnostic tool and received the following codes:

    P0087 - Fuel Rail Pressure Too Low
    P0700 - Transmission Control System Failure

    Does this diagnostic system work for the duramax?
  • This morning my wife left with our 2001 Silverado, she got about a mile down the road and all the dashlights started flashing, the headlights started to dim and she barely made it back home. Truck ran fine but no lights.
  • My truck is haunted! AC goes nuts, DS seat heater comes on and roasts me intermittently. Dash instruments intermittently work, DS AC intermittently blows hot air when PS blows cold. Please any suggestions? I think the problem is a ground going bad somewhere. Can anybody point me in the right direction? Thanks,
  • Hello,

    I have a 2003 GMC Sierra 1500. For Christmas my wife bought me a remote starter for my truck. It was a pretty simple installation after I deciphered the instructions. In summary, the remote starter module hooks up to a bypass module and the bypass module talks to the truck through the OBD2 port to make all the functions work. The only interface points to the vehicle are the brake switch, the OBD2 connector, and a harness that plugs into the tumbler the is turned by the key. So there isn't any wire hacking going on here. So I get it all hooked up and it's working great. Now it's time to neatly tuck everything away and put all the plastic trim back on. While doing this I realize the harness that plugs into the tumbler is going to get in the way of the bezel that goes around the ignition. Under the steering column is this sort of large metal plate that is held in place by 4 10mm nuts. It's obvious that if I remove the plate and tuck the harness under the steering column and replace the plate that everything will fit quite nicely under the dash.

    How wrong I was.....

    After replacing the plate the truck will no longer start. It cranks. The instrument cluster lights up. It catches but does not stay running. Power door locks, dome light, power windows, and probably other stuff also do not work. The power mirrors do work. I completely removed all the remote starter related components and plugged the original plug back into the tumbler but still all the same problems.

    Can anybody help me diagnose this? I checked all the fuses that seemed relevent to any of the failing systems. At this point I'm in over my head, and I have a dead truck. I have no idea what to do.

    Happy New Year and many thanks in advance for any replies.
  • obyoneobyone Posts: 8,054
    If everything was replugged correctly, most likely a short somewhere caused the problem. At this point you might try and disconnect the negative terminal of the battery for 15 minutes and see if that works. If it doesn't you may have to do a wire by wire trace looking for an exposed or shorted wire with a meter. Not something real pleasant to do.
  • I have a 2004 GMC Sierra 1500, extended cab Z71, 5.3 ltr, automatic. It has the heated leather memory seat option. When I went to use the heated seat, neither side will remain on. When I press the seat heater buttons, the lights come on for a fraction of a second and then go out. This started simultaneously on both sides. I also noticed that if I turn on seat heaters while moving seats forward and/or backward, the lights stay on while moving seats and for a second or two after I quit moving seats. I also noticed a click (sounds like a relay making/breaking) from the module under drivers seat when I press seat heater buttons. Prior to this problem, I OCCASIONALLY had a problem with seat memory trying to move the seats all the way forward when keys were inserted. This was only an occasional problem, so I ignored it (out of warranty anyway). Is is possible both are related and can the bottom line be the module under drivers seat? Also: can it be reprogrammed or must I replace it ( if so, what is the official name for it?)? Dealer wants $115 to "check for electrical problem".
  • obyoneobyone Posts: 8,054
    The factory manual has a procedure to troubleshoot your problem. At $115 the dealer is charging about an hours worth of labor which is fair for what you've described.

    FYI, what you're describing is called the memory seat control module.
  • For some time I have had electrical issues:
    I think I have a ground/return issue.
    With lights off, turn signals cause dash gauges to fluctuate in time with the flasher.
    With headlights on, dash lights go out, all gauges to to "zero" & the regular & high beams are reversed, i.e. the indicator is on high beams when they are not.
    Also, I believe something is draining the battery. Connecting a multimeter at the battery reveals a .25A discharge with everything off. Only thing I can see requiring power is the radio clock & .25A (250mA) seems like more than it should be.

    Any thoughts?

    Thanks, John
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