No 4wd, no switch lites, no service lite

[rosier1]

I have yet to find my exact problem on this awesome, informative and very helpfull site. I have an 02 Trailblazer with 79k very gingerly and well maintained miles and my 4WD is not working. Fluid changed at 50k, 4 years ago. My Mode Switch lights are not lit, never noticed when they stopped working. I am an idiot! Also not lit is my service 4WD light on the dash. I pulled fuse #8, looks fine, did the 30 second wait. Pulled fuse #48,looks fine also. When I tried it in September of this year it all worked fine. I try it every couple of months to make sure it works, but got caught in a snowstorm last weekend and nuttin. I am hoping TCCM. Any thoughts would be greatly appreiciated!! And where is the TCCM? Steering column?

BTW......Krylon Fusion painted bumpers that I did in August are still looking great, no changes to them yet!

[ErikSS]

I am NOT an expert in auto electric, but I have 1 idea. If the service 4x4 light isn't on, it seems the self diagnostic system hasn't detected a problem. The lights don't come on the switch, and 4x4 doesn't work. After checking fuses as you have, that would lead me to the switch itself. They can be bought at Carquest pretty reasonble.

[DirtyBacon04]

I am NOT an expert in auto electric, but I have 1 idea. If the service 4x4 light isn't on, it seems the self diagnostic system hasn't detected a problem. AThe lights don't come on the switch, and 4x4 doesn't work. After checking fuses as you have, that would lead me to the switch itself. They can be bought at Carquest pretty reasonble.

Easy fix.

[Moots1288]

Yup.. it's problematic on the 02s

[TBYODA]

Not sure if this part is any good or not
Dorman 901-064

http://m.summitracing.com/parts/rnb-901-064 about $18
Amazon same on prime
Rockauto
http://www.rockauto.com/catalog/x,carco ... type,10775

[rosier1]

Thanks guys!! Easier fix than I planned on. Another dumb question. How to remove the switch?. Pull the dash panel apart?

[DirtyBacon04]

Hammer... the bigger the better...

[The Roadie]

The switch pries out. But let's back up a second. When you turn the ignition on, the lights on the switch should all come on for a second as a lamp test. Does this not happen?

For a 2002, the TCCM is a huge suspect, but when they fail, the PCM detects the lack of communication and turns on the "Service 4WD" lamp. If this isn't happening for you, you may have something unique to troubleshoot. Do you have a voltmeter and any experience in electrical troubleshooting?

The TCCM is above the driver's left knee, mounted to the top side of the trim panel underneath the steering wheel. Here's a picture, but I guarantee you will not have to disassemble your dash to this extent to see it.

[rosier1]

No lights on the switch at start up. No lights at all, thats what makes me suspect the switch. I do have a volt meter and am not afraid to use it.

[Regulator1175]

With no lights at all I would certainly look at the switch as the problem. Any friends around with a Trailblazer that wouldn't mind helping you do some trouble shooting? Try a functioning switch from another truck and see before you spend the money. Maybe a test drive from a local car lot?

[rosier1]

I ordered 1 from amazon to get me through for now. $30 delivered. But want a better brand name. Just gotta get it working now.

[The Roadie]

The lamp test at ignition ON time depends on a working TCCM, but it also depends on a good dimmable lamp bus connection. Are any other interior/dash lamps out? If many of them are out, then it could also be a blown TBC fuse (2, or 4, I forget which one feeds the mode switch). Or of course front fuse #8.

If you have the schematic, I'd be putting a meter on the back of the switch while you wait for the replacement to arrive. Look for 12V on pin B, purple/white. That's the dimmable lamp feed that is required for the lamp test. And look for 5V on pin J, a gray wire. And somethign lower than 5V on pin K, light blue, and that voltage will vary depending on the mode the switch is in.

[rosier1]

Actually I just noticed that the light on the battery or oil is out. Its the one on the top right, closest to the switch too. Damn man, your good! I will go check fuses as soon as I can. Thanks a bunch!!

Sent from my SCH-I535 using Tapatalk

[rosier1]

Fuses are good.

[The Roadie]

So check to see if the voltage from the good fuse gets delivered to the switch on the pins I posted.

[rosier1]

Replaced switch. No change. Found a TCCM at a local junkyard for $85. My mechanic buddy is going to see if it threw a code. I wonder if it were to be flashed, it'll straighten out. Breaking out the meter first.

[rosier1]

Hooked up the Snap on scanner. Got a U1000 code. Still no lights on the switch, even at startup. Still no service 4wd light either.

[The Roadie]

Checked any of the voltages on the TCCM or the switch yet?

[rosier1]

All the voltages are what they should be. The TCCM is communicating with the code reader. Code U1000 class 2 comm problem.

[The Roadie]

Hmmm, pull stuff out of the data comm splice packs until the tccm communicates with the pcm? You sure have a weird one!