Ongoing intermittent 4WD issues

[gruvedaddy]

So, here's the rundown of what's been going on , what i've done and where i'm at. The Service 4WD light has been on steady while in 2WD in all kinds of weather, rain, snow or shine, for about a year now, but occasionally goes away and 4WD does work, but then light comes back on and away goes 4WD. The 2WD selector switch light is on steady as it should be, but I changed it with a new switch as it was only 20$ or so, but the problem remained. Then i bought and installed a new encoder motor, but the problem remains. Didn't want to keep throwing cash into parts that i apparently don't need , so i bit the bullet and had the truck scanned with the Tec 2 scan tool for $100. They came up with front differential actuator is not engaging, and recommended replacing it. So i purchased a new actuator and swapped it out , but guess what? The problem remains. The intermittency is what bothers me. I am an Electrician and know intermittent issues are typically an electrical connection issue, but i'm not sure how to even start to troubleshoot this. I think my next step is checking the connectors on the TCCM to see how those look. The mechanics said the Tec 2 didn't see any faults other than the actuator not engaging, no TCCM codes or anything else. But, of course, they weren't able to give me a print out of what the tool found. The only bright spot in all this , i guess, is that i did all this swapping out myself and saved 600$ or so in labor alone! Thanks to all who contribute here, your knowledge is invaluable. Now, what's my next step? Would the fuse pull trick allow the TCCM to see the actuator?

 

[The_Roadie]

1) Please fix your profile. You can't have a 2012 TB.

2) If you have a 2002, it may be a bad TCCM. Many of the first revision ones have failed. Replace it with a junkyard 2003+ unit.

3) You can exercise the front axle actuator when it's unbolted from the splined disconnect. See if the noise or the behavior of the lights change.

4) Do the fuse pull trick, but from then on, observe the light behavior very carefully. When exactly does the Service 4WD lamp go on?

 

[gruvedaddy]

Ok. I'll do the fuse pull trick today. I've been keeping an eye out for TB's at all the local yards and have yet to see any come in. Been asking around to see if anyone i know knows someone with a 2003 or newer TB so i could try a TCCM swap and see if that does the trick. The service 4WD light is on about 90% of the time. Sometimes it goes away while driving, sometimes on initial start up. But it always comes back. I'll also try disconnecting the actuator and see what the lights do. I can hear both the actuator and encoder motor doing their thing, and they both sound like what you and others have described they should if they were working correctly. I'll let you know how it works out. Thanks.

 

[The_Roadie]

The service 4WD light is on about 90% of the time. Sometimes it goes away while driving, sometimes on initial start up. But it always comes back.

The exact sequence of that behavior might contain a clue. At ignition on, when the lamp test is flashing all of the mode lights on the selector switch, is the Service4WD light on? What time does it take for it to initially come on if it isn't on right after the lamp test? If you put the mode selector into A4WD, and the Service4WD lamp is off, what is the exact behavior of the switch lamps and the Service4WD lamp?

The clues are sometimes subtle to observe if you don't have access to a TechII tool to directly command the TCCM to run through its paces.

 

[gruvedaddy]

As usual the service 4wd light has vanished yet again. I am troubleshooting the 4x4 issue in the garage at the moment. Part of what i'm lookin' at is explained in this post i did in the old forum a year ago. "The fuse block that is located under the drivers side rear seat has a sloppy/ intermittent connection on fuse 44 (HVAC), thus creating my HVAC to also be intermittent. What i am wondering is what color is the wire that comes out of the fuse block and goes up front to the fan switch(or wherever it goes) ,so i can bypass the bad fuse and put a fuse holder in seperatly next to the fuse block. And what color wire feeds that "bus" that feeds the original fuse. It's not as simple as taking the block out and physically looking as i have tried this. I am also having 4WD problems and am wondering if the fuse holder for the 4WD, which is right next to the HVAC fuse, is also bad. Any help is MUCH appreciated."

I took my 12v troubleshooting light and checked the 4 pin plug going into the TCCM. With or without the ignition on i have voltage on pin B (orange) but not on pins A,C and D. I am able to shift between 2HI, 4HI, and A4WD.

 

[The_Roadie]

The 4-pin plug, orange wire, C3, pin B, has constant power, as you discovered, from front fuseblock fuse #8. It goes to the transfer case encoder motor brake also. The intermittent fuse you mentioned is rear fuse #48, and it powers up the front axle actuator on a brown wire that bypasses the TCCM altogether. If you want to improve the reliability of THAT wire, you will have to locate a brown wire on connector C1, pin E8 at the rear fuse block. Oddly enough, its reliability might be reduced by a long path it takes THROUGH the front fuse block in a hidden connection from C2, pin B11 to C3, pin E4. I assume they did that to make the signal easier to get to the chassis wiring harness to get down to the front axle actuator.

I highly recommend NOT using a test light on circuits like this that also involve sensors. A meter is much safer and doesn't run the risk of activating or affecting a control or sensor circuit. Test lights are good for troubleshooting lamp circuits only, IMHO as an electrical engineer with a 38 year career.

 

[gruvedaddy]

Wow. I think we're on to something. The Tech 2 scan tool showed the front actuator not engaging. I'm thinking this fuse block issue could be the culprit. What i'm going to do next is locate the brown wire you mentioned coming out of the fuse block , snip it , and re-feed it through an inline fuse of the same amperage. I also want to do the same thing with the HVAC feed off fuse 44, do you happen to know off hand which wire that may be? I do have my meter here now , so i'll use it instead of the test light. Time to fire up the garage heater and get busy. I'll check back in a bit. Thanks again Roadie!

 

[The_Roadie]

HVAC Fuse #44 also exits the fuse block on a brown wire. Connector C1, pin D8.

Here's the schematics you need for the 4WD system. Let me know if you need some theory of operation for the front axle actuator.

View attachment 17681

View attachment 17682

 

[gruvedaddy]

Thanks for the schematics roadie. After a couple hours in the garage i successfully tapped into the "run" bus feed (orange wire), added 2 new inline fuses, and connected them to the appropriate wires in place of fuses 46 and 48 in the rear fuse block. So far so good, but only time will tell. That fuse block is such a bad design, in my opinion. I'll check back and let ya'll know if this fixed my 4WD issue. I feel it probably did resolve it after seeing that the 4WD actuator and the HVAC blower are both fed off the "run" bus, and those two sit side by side and were the ones i was having problems with. Thanks again roadie, and i'll let ya know how it's going soon.

 

[gruvedaddy]

Well, it's been 10 days since i repaired what i believe was a bad electrical connection in the fuse block under the rear seat. And since then , no problems!!! :wootwoot: The 4wd has been working like a charm. Typically the problem would return after a couple days in the past. But this time i think we got it! Thanks again Roadie! And to all who contribute here!

 

[The_Roadie]

Glad to be part of the solution. You did all the heavy lifting.

 

[DarkBlazer02]

Hi I was hoping someone can share some light on this.... I have a 2002 Traiblazer and up till bout a month ago all was good but now its colder outside my 4wd light is on and no lights on the switch..... now after the truck is warmed up and driven a few miles if I stop and shut the truck off and turn it back on all is good everything is working! All i can figured out its diffidently heat related! I have no idea where the TCCM is located at! But this thread sounds something like mine but if anyone can help I'd appreicate it!