2003 Service 4WD light at speed

[voy_blazer]

Hi folks,

I have some observations and tech questions that I hope The Roady or similar educated folks could chime in on. It's an '03 ENVOY XL SLE 4.6.

yes, yet another case of "service 4WD" indicator in the instrument panel. I have read previous posts on this site and TrailVoy about slightly similar cases, but I feel this case differs from the rest.

When I move the selector from 2W HI, to A4WD or 4HI, it engages no problem. In neutral and stopped the 4LO engages no problem. Selector light properly illuminates in accordance to its position, no problem. While stopped and in neutral I can go through all of these selections flawlessly, hearing the telltale signs of proper engagement and disengagement. I mainly run in 2HI, and when necessary to trail or snow conditions I will engage 4HI or 4LO. I usually don't find A4WD useful.

This is where the problem begins: When I drive over 15-20MPH in a 4wheel position (any,) the infamous "service 4WD" light comes on. When this happens, I cannot disengage any of the 4WD selections....until I shut the truck off and restart. Then the desired selection is initiated, noted by the indicator light on the selector, and the telltale sounds of the engagement or disengagement for 2HI. I also noted a rubbing or honing sound similar to that of a dry bearing. This is predominantly on the drivers front axel area. But know the wheel bearing is in good shape. I have ruled out the TCCM, and the actuator motor, because they are obviously working.

I took it to Advance Auto to put it on the code reader, and it only came up with a missing wheel speed sensor code, and brake control module issue code. I assumed these are irrelevant to the issue at hand. I also noticed (though may also be irrelevant) a bumping sensation when I come to a short stop. However, with this collective evidence, is it possible there is a bad bearing in the front diff on the drivers side? Could this disengagement issue and "bump" be related to that, if that where the case? FYI its not any suspension issue, though I am lifted. All of the links and suspension parts are rock solid and fresh. Further more this is not a new issue, it's been this way since I got the truck, and just blew it off due to good weather. Of course the snow is flying now, and I want to play with my 4X4 in the snow. So I welcome any takers on any possibilities I may have overlooked, or if in fact my bearing thought holds any ground.

 

[The_Roadie]

... it only came up with a missing wheel speed sensor code, and brake control module issue code. I assumed these are irrelevant to the issue at hand. ...

Welcome, glad you found us after the great jailbreak from trailvoy, and that assumption is your problem. The TCCM requires accurate knowledge of the RPMs of each front wheel (using sensors at each wheel bearing) and the rear driveshaft (using a sensor at the tailpiece of the transfer case.) These sensors are small, and corrode, and new ones come with new bearing assemblies, but can also be changed out separately. The sensor or the wiring or connectors back to the TCCM are bad. Start with a close visual inspection.

View attachment 31577

 

[The_Roadie]

I also broke off your new issue into its own thread to avoid hijacking the similar one you posted in.

 

[voy_blazer]

Welcome, glad you found us after the great jailbreak from trailvoy, and that assumption is your problem. The TCCM requires accurate knowledge of the RPMs of each front wheel (using sensors at each wheel bearing) and the rear driveshaft (using a sensor at the tailpiece of the transfer case.) These sensors are small, and corrode, and new ones come with new bearing assemblies, but can also be changed out separately. The sensor or the wiring or connectors back to the TCCM are bad. Start with a close visual inspection.

View attachment 18641

Ok, so I put the Envoy up on the lift today to try and get a better diagnosis. After engaging the 4WD mode and removing the wheel this is what I found:

1) Inspected wheel hub operation and found no play.

2) Inspected wheel sensor wiring from hub to TC. Found no obvious damage or corrosion to wires or connectors.

3) * Rotated rotor by hand and noted smooth rotation for half a turn then slight resistance for the other half.

4) Inspected both inner and outer boots on the axel to find no obvious damage (tears or leaks.)

5) * After further inspection I found an axel seal leak at the differential.

So collectively, I am assuming 1 and or 2 scenarios(hopefully not the ladder of the 2) :

1) I am pondering an axel issue itself, as well as an axel seal to the diff.

2) Both axel, seal, and possibly a bad bearing in the differential itself.

So I picked up a new axel and seal, and I will start from there tomorrow. I will be posting back with the results...wish me luck

 

[The_Roadie]

All of the things you found were useful things to fix. But not at all related to a sensor fault that would cause the Service 4WD light to go on. Unless flung grease got into the connector and causes an erratic connection. Also recommend you unplug and replug both sides sensor connectors to clean up the contacts if that's the issue.

 

[voy_blazer]

Ok folks,

So I have now replaced the axel, and axel bearing to the differential. Still same issues with the "howling" sound and "service 4WD" light still comes on. So then I replaced the wheel hub bearing assembly complete with wheel speed sensor. Yup still got the pre-existing issue. I fear my original dread, which may indeed be bearings inside the differential itself. So frustrating to be putting all this work into my en-toy, and still be having the same problems. at least we're ruling things out. Wish me luck guys, and I welcome any constructive feedback. I will continue to update this thread until we've nipped this in the bud.

 

[linneje]

I think that you need to call in the big dog for this one ... (that is what my tire shop calls it). You need a code reader that can read live streams if you are going to get to the bottom of it. I have my own code reader, but it only does emission codes. Occaisonally when I need some live data I can borrow the "big dog" and read a data stream live - if you don't have access to one you can borrow you might need to get someone at a shop to take a ride with you and catch data (because you can reproduce the problem) - you just need to pick the right stream to monitor.