Intermittent Electrical Issue | 2004 Chevrolet Trailblazer

2004 Chevy Trailblazer

2004 Chevy Trailblazer

This 2004 Chevy Trailblazer came in with multiple concerns. The main issue was intermittent low power. When this happened, the customer said that the Electronic Throttle Control, ABS, Traction Control, and sometimes the 4WD lights would come on. When the lights were on, he also stated that the cruise did not work and the HVAC and blower motor would quit working. First thing I did was scanned the truck’s multiple modules. These are the codes I found –

PCM – U1041 lost communication with ABS Module

Ignition Switch Wire Diagram

Ignition Switch Wire Diagram

TCCM – B0790 transfer case neutral indicator circuit, C0379 front axle system, u1000 class 2 communication malfunction, u1041 lost communication with ABS Module

HVAC – B0263 HVAC actuator circuit, B1375 device ignition 3 circuit

IPC – U1041 lost communication with ABS Module

SDM – u1000 class 2 communication malfunction, u1041 lost communication with ABS Module

From the codes only I am leaning towards a bad ABS module that is bringing down the communication circuit causing the loss of throttle control. Could be a power or ground issue also.  I didn’t start testing in that direction because the customer stated he would lose is blower motor control every time this would happen. That one statement changes everything because a communication problem has a low chance of bringing down a manual HVAC systems blower motor control. So I went for a wire diagram of the blower motor circuit and also the power feeds for the

Chevy Trailblazer Ignition Switch

Chevy Trailblazer Ignition Switch

HVAC module. Referencing HVAC code B1375, I looked for the ignition 3

Chevy Trailblazer Defective Ignition Switch

Chevy Trailblazer Defective Ignition Switch

feed circuit. Fuse HVAC 1 feed that circuit. With this being an intermittent issue testing is going to be tough. So my next step is to see what feed HVAC 1 fuse and try to link that power feed to my other concerns. IGN A fuse feed to the ignition switch. From the ignition switch, power feed from the run position on circuit 300 which feeds the HVAC, 4WD, HVAC 1, Brake, and TBC Run fuses. Do you see the connection? With the ignition switch feed fuse IGN A good, the biggest common failure point would be the ignition switch. A new ignition switch fixed the customers intermittent electrical concern.

Leave any questions or comments below. Thank you.


  • Ray Yergeau says:

    Good work, Thank you


  • Jason says:

    I have a 2007 TB LS and all of a sudden about a month ago, I am having intermittent starting problems. I have changed out the Alternator, 2 batteries, Ignition Switch and I am still having the same issues of it not wanting to start here and there. Every time I change something out it takes about a week or less and then dead again. I have noticed when it does not start, I have low lights or no lights inside of the truck as if the battery is dead. I have a drain somewhere??? I was told the battery cables could be the problem or I could have a bad starter cylinoid. I have also checked the ABS motor and made sure all lights were off when the doors close. All lights are working properly. When running, it runs perfectly. Does anyone have any other ideas?

    • Travis Dewitz says:

      First step in testing this that I would take is to do a parasitic draw test and see what the amperage is. Anything over 500ma is too much and I would typically see much less after pcm shut down.

    • michelle says:

      how do you fix this electrical prob with my 2004 trailblazer? ????????pls help

  • Jason says:

    Thanks for the responce but I have no clue what you are expalaining to me. I have had the battery checked along with the new Alternator and the Volts to the battery are correct. My mechanic also volt tested everything and all seems to be functioning correctly.

  • Jason says:

    When you say check for battery draw, what am I checking and from where to where?

  • jit says:

    please advice weich please come transmission oil pressoure sensor

  • Ken says:

    I have a 2008 Trailblazer that I had the steering wheel position sensor replaced in Oct. Ever since then, the truck has had very intermittent no starts, The battery is new, when it starts, plenty of power, but it does seem to draw more voltage from the alternator since the SWPS was replaced. They replaced the ignition switch, and 3 weeks later another no start. Fuses check fine, no codes, the only light that comes on when it won’t start is the check engine light. Everything else pretty much goes dead. Any ideas what to check next?

    • john says:

      when you start vehicle you are not affecting the alternator, only the battery and the cables

  • Tina Baye says:

    intermitten dash lights brake,abs brake 4wd all lights flash, replaced switch, alternator, checked grounds I can find, feeds coming in. any ideas?

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