Intermittent Electrical Issue | 2004 Chevrolet Trailblazer

Intermittent Bad Ignition Switch Causes Low Power and No Blower Motor

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
  • 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 but this could also be a power or ground issue.  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 HVAC module. Referencing HVAC code B1375, I looked for the ignition 3 feed circuit. Fuse HVAC 1 feeds 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 is the feed to the ignition switch. From the ignition switch, power feeds 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, since people really care for their cars when they use it for personal use or for transportation services like Uber and that’s why they also compare uber insurance and save money to make sure their car is always safe.

Leave any questions or comments below. Thank you.

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Comments (28)

  1. Jason

    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

      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

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

  2. Jason

    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.

    • Travis Dewitz

      You need to check for excessive battery draw and how much draw there is.

  3. Jason

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

  4. Ken

    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

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

  5. Tina Baye

    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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  7. Krissie

    My 2003 trailblazer is intermittently starti.g…the dash lights come wo t work..piwer windows/locks won’t work and now it wont start….I’ve replaced the 125v fuse..any suggestions??? Sometimes when I slam the back hatch it will be normal again

    • Katie

      This is a very late reply but if the motor is out on the back windshield, this can cause issues with the electrical components. I have to reset it by opening and closing my hatch as well.

  8. Rogue

    My 04 trailblazer wont crank, replaced starter relay.I turn the key and theres sounds under the hood as normal, but on the dash only the srrvice engine and battery symbol illuminate.

  9. JJL

    I have a 2007 Trailblazer. I’ve gone thru 2 alternators, and 2 ignition switches. Lights alarming on the dash, blower stops working. Deinetly a ground issue somewhere, occasional whine/whistle thru the speakers, usually after a good bump in the road….another good bump will ‘fix’ it temporarily. Very challenging finding the root of the problem. Once thought may be related to using cruise control, seemed frequent when CC used….may be coincidence ? Anyone with similar issues ? Any resolutions ? Thanks !

    • Juan

      It definitely has something to do with cc. I bought my vehichle at 110k miles and didnt start using my cc until about 145k and ever since I’ve had issues

    • 2006 BUICK ALLURE was acting like that change starter still the same ,open fusee box press on every fuses and breaker try cranking and it started work the very bes ever since good luck.

  10. Josh

    I’m having all of these problems on my 02 tb, replaced the ignition switch 4 times in a little over a week, god I wish I could figure out why it keeps burning out, it’ll start up fine, but if I start it and those lights come on on the cluster I know if I turn it off and try to restart it it will not start, every time it’s random things that will not work also like power windows, front or rear wipers and my radio hasn’t worked in a while while it’s running, it used to then sometimes now never, only when not running

  11. Laura

    I have a 2005 TB LS. I have no low beam headlights, it wont crank, stuck a t pin on the one post of the start relay and as soon as i touched it with my test light the engine began to crank, i pulled the test light and repeated this several times. I have cleaned all the chassis ground that are along the drivers side fender under the hood, I am just stumped. also along with these issues my windshield wipers are not working, but you turn them all the way to high they turn on, you slow them down but they will not shut off. I am at a loss of where to go. I thought maybe it was in my ignition switch….but what about a neutral start switch? Any ideas?


  12. Brooks

    I have a 2005 TB EXT. I am experiencing Fuse 16 under the hood popping as soon as I turn the ignition off. When I replace the fuse, the vehicle operates normally until I shut it off, then Fuse 16 pops again. Please help.

  13. Don

    I have a 2004 Chevy Trailblazer I started up as an idol my lights flash inner lights outer lights and even on my dashboard lights they all flicker I changed my belt tensioner and change my belts and they flicker worse than when I had the old Parts on anybody have an idea what I got going on thanks

  14. Karl

    We have a 2004 LS Trailblazer that is having strange electrical problems with only 23K miles. Intermittently the service 4WD, ABS, Brake dash lights would stay on after starting engine. At the same time the heater blower would not work, the radio wouldn’t turn off after turning the engine off and opening the door, once out of the car and pushing the lock button on the door, instead of chiming 3 times and locking 5 seconds later, the chime was silent and the doors locked immediately, the FWD switch lifers would just flash when changing positions but the trans wouldn’t switch, once back in 2WD the light would stay on steady.
    So after reading all the problems others are having I replaced the ignition switch and left the battery disconnected for several hours. Everything seemed to work fine after that for several days. Then the radio stopped turning off, and the door locks went back to instantaneous again. Everything else appears to be working fine.
    One other intermittent problem is a check engine light. It is very intermittent but has been throwing a PO455 code for several years now. It’s a code for a large evap leak. So far I have replaced the gas cap twice, the last one was a GM cap. Also replaced two valves in the system, one on the engine and the other in the back by the tank. All the pipes and hoses look good as does the gas filler pipe. This is my wife’s car and she won’t even ride, let alone drive it anymore! I want my p/u truck back! Please help, Karl

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  16. Mike Dezserres

    My 04 TB LT wont start no power Battery is charged but still no Inst cluster and cant remove the y it turns to starty position thats all ?

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