ABS Light On, No Codes after transmission replacement

Mike Technician Atlanta, Georgia Posted   Latest  
2004 GMC Savana 2500 4.8L (V) 4-spd (4L80-E)
No Codes
No Symptoms

Repaced the transmission in this today and did a rear brake service. Used a reman from GM dealership. Did not disturb the ABS unit nor harness. After installation, started the vehicle and had ABS and Brake lights on. Scanned and had no current nor history codes. Cleared and the light went out. Next key cycle it came right back on.

In scan data, it does show that the ABS module is requesting the ABS and brake lights on. Brake fluid level pid shows ok (I was hoping that was it!)

I can use the scan tool to clear codes even though there are none and the light goes out. Brakes perform normally on test drive, all wheel speed sensors working.

Next key cycle when the light comes back on, I look in scan data and the pids for LF dump valve feedback, RF dump valve feedback, and rear dump valve feedback all read 'ON'. Rear isolation valve feedback and RF isolation valve feedback will randomly switch between 'OFF' and 'ON'. This is KOEO sitting in my bay, not on the road. Command pids for all valves read 'OFF' so it looks like the ABS module thinks there's a problem.

I checked powers and grounds. Blades on the maxi fuse are clean and making good contact. Terminals in the ABS connector are clean and dry. No codes in any other module. And as I said, performs normally on test drive after turning the light off with the scanner. I didn't see where any reprogramming was necessary with a new transmission on this vehicle. Tomorrow I'm telling them it looks like we have a bad ABS control module. I'm just trying to figure if there is any way at all the transmission replacement could have caused this.

Stacey Technician
Brantford, Ontario
Stacey Default

Mike do a voltage drop test on the ground side from the battery to frame. That vehicle line was terrible for the braided ground cable on the passenger front of the block rotting out.

+2 Default Ð Bounty Awarded
Ray Diagnostician
North York, Ontario
Ray Default

Stacey is right, pull on the braided cable with a tool.

+1 Default Ð Bounty Awarded
Kevin Mechanic
Painesville, Ohio
Kevin Default

I have never seen a replacement transmission cause what you are experiencing. As has been stated, the ground braided cable causes all kinds of issues. Do you have a brake fluid level sensor on the truck? Check the emergency brake switch.

0 Default Ð Bounty Awarded
Mike Technician
Atlanta, Georgia
Mike Default

It's a van. First thing I checked was brake fluid level as low brake fluid will turn on both lights. Not it. Same with the parking brake switch. I agree that one would not expect a transmission replacement to cause this and I don't think it did, but it's odd that it started after the replacement.

0 Default Ð Bounty Awarded
Rudy Technician
Montebello, California
Rudy Default

I 4th the ground issue. Additionally, the ABS modules on these things have such a high failure rate, that they are typically on national backorder. Dorman is the only aftermarket supplier that remans these(that I know of) and are readily available. We went that route twice. And both times the modules failed with in a few months.

0 Default Ð Bounty Awarded
Mike Technician
Atlanta, Georgia
Mike Default

We have had good luck getting AC Delco EBCMs here in Atlanta from the dealership as well as from Parts Express. New EBCM will be here Monday. Ground was good (20mv voltage drop) but I ran a new ground cable anyway just to be sure.

+1 Default Ð Bounty Awarded
Mike Technician
Atlanta, Georgia
Mike Update

All, thanks for the advice on checking grounds. I rechecked this morning. The braided cable from block to frame rail was intact. Voltage drop from EBCM ground to battery - was 20mv. Nevertheless, I went ahead and added a new ground cable from G300 where EBCM grounds to the engine block. No change.

0 Update Ð Bounty Awarded