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.

Leave any questions or comments below. Thank you.

Automotive Diagnostic Scope Training ManualThe Automotive Scan Tool, Scope, and Waveform Training Manual is just over 40 COLOR pages long and is full of images, tests, information, tables, conversions, and common problems. This manual is focused on advanced beginners and intermediate users. Advanced users would also find this manual very handy. The main focus of the manual is on scope usage, interpreting waveforms, and utilizing your graphing scan tool(s).

Great guide for Snap-On Modis, Versus, and Vantage Pro users but the manual is designed for all automotive scopes in mind. This great resource includes useful charts and tables, scope waveforms, graphing scan tool testing tips and tricks, along with scope test lead and low amp probe test hook up location diagrams. Sensor tests include O2, TPS, VSS, MAF, CKP, CMP and MAP. Other component testing includes fuel pumps, coils, starters, blower motors, and fuel injectors. Ford Mode 6 misfire diagnostics and Ford coil on plug (COP) testing tricks included. Tricks include two test lead hook-ups to diagnose how many coils and which cylinder coils are bad, even before the customer knows! Download Now – $15

Comments (15)

  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?

  6. I’m truly enjoying the design and layout of your website. It’s a very easy on the eyes which makes it much more pleasant for me to come here and visit more often. Did you hire out a developer to create your theme? Fantastic work!|

  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

  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 !

Leave a Reply

Your email address will not be published. Required fields are marked *

Get in touch with us!

Big or small, we’ve got a solution when you need it. Our advanced service and support tools provide step-by-stepinstructions without being put on hold or waiting in line.