ABS and TC lights
 

This message is primarily for HUMMTECH but PMs seem to be down, so I'm posting here. Feel free to reply.

Went wheeling through some deep (2-3 feet pretty consistently), icy water and got TC, ABS, and Parking Brake lights on and off the whole time. It's been a month and I've still got the lights on. Not always all three...but always ABS and TC.

I just pulled the positive off the battery, checked the rear wheel speed sensor cables, pulled the sensors out, cleaned everything and put it back together and took it for a drive. I still have the lights.

Thoughts?

Thanks in advance.

Re: ABS and TC lights
 

Did you scan for codes?

Re: ABS and TC lights
 

Sorry...forgot. No codes at all.

Re: ABS and TC lights
 

I am definitely not HT, and I know that you probably know more about these "rigs" than I do, but do you think that possibly its either a computer issue (ie. you got the BCM or something wet), or the sensor (ie. they are wet or damp or something.... even though I know you cleaned them and such) or that maybe the dash is malfunctioning?

Plus the fact that it is an intermittant problem....
Do you have anything that is not performing correctly to correlate with the light?

Again... not an expert but based off standard GM OBD I would think that if you have a light you should have a code... sometimes you even have codes with no lights (Ie. no CEL on my vette, but I have a couple of codes pop up on every start up because the O2 sensors are not a fan of my headers)

Re: ABS and TC lights
 

What did you scan for codes with? If its a code reader it wont pick up chassis codes. Need a pretty good scan tool to get codes from ebcm. I would start there but you could look at transfer case speed sensor wiring and connectors for damage, water intrusion in connector at speed sensors. I bet there is codes set in ebcm with those lights on.

Re: ABS and TC lights
 

I used my SuperChips Cortex programmer to look for codes. I'll check the transfer case tomorrow and maybe swing by the old Hummer dealer to have them scan it.

Thanks...I'll report back.

Re: ABS and TC lights
 

I checked the cable going into the transfer case. There's no visible damage...it was mud crusted, but I disconnected it, cleaned it, applied some dielectric grease and reassembled. Took it for a drive...still got the lights.

I was feeling lazy so I took it to Advanced Auto to have them pull codes instead of the dealer. Here's what came up on their scan tool:

U1305
U1000
U1040
U1016
P1626
U1301

Most of these seem to deal with serial communication errors. I'm starting to think that I've damaged some part of the on-board computer system. I also noticed that the 4WD is out. I can no longer switch to 4HI or 4LO.

LOL...looks like I'll be off to the dealer before my next adventure.

Re: ABS and TC lights
 

I will throw a guess out that you have lost communication with your electronic brake control module. Check abs fuses and inspect connector at abs module for damage or contamination.

Re: ABS and TC lights
 

I had a feeling there was a computer issue based on the fact that usually if there is an issue with that much involved in the Vette it has to be a bad sensor, wire, or module.

Did you have them clear the codes to see if they were active or history codes?
I always do that because active codes will mean a broken something. The codes will not clear. history codes will give u issues but if cleared and they never come back then it was probably a one time drop in voltage or something.

(ie. after I had the s/c installed on the Vette my car would constantly drop into "limp mode" for no reason. Sometimes if i floor it, other times if i dont. Sometime if i just drive it normal.... there seemed to be nothing to cause it. Since the installed was in a far away state I couldnt easily bring it to them, so 1500 dollars later my tech finds it is the crimp connector used for the TB. turns out these computers are so sensative that the slightest drop in voltage will through a code. After a quick clip clip and solder, the car has been strong ever since.
I assume the Hummer is the same way

HT, do you think the ebcm or the abs module is causing the issue with his inability to shift his 4wd?

Re: ABS and TC lights
 

Not sure on that. If you can clear all codes and it still wont shift that's where I would be looking for a failure. History communication codes are the hardest thing to diagnose. As per GM diagnostics you should never even chase one. Any module on the data line can be causing the problem. Don't remember if I asked but do you have a remote starter installed? P1626 tells me you might have one as its a security code. If you do the security bypass module for the remote starter could be root cause and that's where I always start for these type of issues.

Re: ABS and TC lights
 

if not remote start the reason I would suspect ebcm is that its under the truck and ucodes that are set would be typical of that module causing a communication issue. If the ebcm is causing a data line problem the only module downstream of it is the transfer case shift control module

Re: ABS and TC lights
 

OK maybe I am a little nieve on these rigs, but doesnt it sound a little "off" for Hummer to place a computer outside the truck in an area that could easily go under water?

(Especially since these things are designated to be a more extreme off road vehicle?)

Re: ABS and TC lights
 

Yep...there's a remote starter on the truck. The previous owner installed it. I've looked at pulling it several times, but it seems to be wired in in such a way that it can't be easily removed. HT, you're probably correct about that causing the P code, and I'm not convinced that the P code is related to everything else that's going on. I also recently installed a 'new' factory head unit...I thought this might be involved in the P code, but the unit works fine and was programmed for my VIN.

jsbihn, I didn't have them clear the codes. I think I'll probably swing by Pepboys this morning and grab me a good scanner to keep on hand. I'll clear them myself and see what happens.

I've also gotta pull up the EPC and figure out where the ABS module is located. The ABS fuse (60 amp, front fuse box) is good.

Re: ABS and TC lights
 

Checked the ETC fuse (15 amp front fuse box)...it was good.

I found the ECBM up under the frame, driver's side...there's no physical damage that I can see. I couldn't figure out how to get the connector loose from the module to see if it's be contaminated, and it's a bit cold to be hanging out under the truck today. I'll figure this out later.

Going to grab a scan tool now...

Re: ABS and TC lights
 

HT,
Will a ELM 327 be able to scan down enough?
It appears on my Vette, it doesnt pick up all the codes that the car's ECU will scan and clear, but I could be wrong.
So I was wondering if it acted the same on the H2

Re: ABS and TC lights
 

I grabbed an Innova 3130c...it picked up the P1626 and U1301. I cleared the codes and fired it up...still got the lights. Shut it down, rescanned...no codes reported. The 3130 is suppose to report ABS codes/status on GM vehicles too, but the tool reports that ABS communication with this vehicle is not supported. Weird...I'll have to research that a bit on Innova's site.

I'll drive it for a while and see if anything changes. I'll probably look at the EBCM again tomorrow...supposed to be a tad warmer.

Re: ABS and TC lights
 

Try this. Right behind the data link connector where you plug scanner in you will find a wire spliced into the data line(purple wire) cut the added wire in a way you can reconnect it later. Then attempt to clear codes and see what happens. If the remote start is causing a data line failure this will eliminate it.

Re: ABS and TC lights
 

HT, I'll check this out tomorrow, although I really don't think the remote starter is the culprit. You seem to know your business...so I'll definitely follow your guidance and report back.

I returned the Innova scanner as I wasn't entirely happy with it. The 'tech' at Advanced Auto used an Actron when he scanned and he got more codes than I got with the Innova. So I swapped the Innova 3130c for an Actron CP9580. The 9580 pulls the same codes that Advanced got (those listed earlier in this thread - minus the P code...that hasn't returned).

I used the Actron to clear all codes across the board. After firing the truck back up I got the U1000 only. My gut tells me that I'm going to need the dealer to slap a Tech2 on it to really get a diagnosis.

Re: ABS and TC lights
 

And 4 wheel drive buttons still don't work?

Re: ABS and TC lights
 

So with the Actron you were able to clear all the code except the U1000 communication code?
So did the lights stay on the dash?
Have you experienced any difference in the way the truck runs?
Do you still have the issue with the transmission not being able to switch out of the selected 4WD?

Also, why do you think a tech2 will perform any different then what your Actron has performed?