2002 Tahoe 4x4 with ABS light coming on

Fortune50 · March 9, 2007

HI, my buddy's '02 Tahoe Z71 5.3L (E-85 compatible) 4x4 w/ 3.73 gears has an issue with the ABS. The truck has 75K miles on it. He has had the ABS light come on the last 2 weeks after every time it's put into gear and starts moving. The red brake warning light stays off. A recall repair was performed on it yesterday at the Chevy dealer to check for corrosion on the wheel sensors. They replaced the right front one as it kept reading low, but it was not the cause of the ABS light coming on, apparently. The truck has two trouble codes: C0281 (and P0268 which I was told was stored in "history"). The truck seems to run fine except for the ABS light. He did just recently have to replace a burned out bulb in the rear right tailight for the brakes.

So how do I go about diagnosing the C0281 code? I have a DMM that I've used extensively over the last 15 years. Do you think it might be the EBCM? I've read about the issues with them staying on, but his doesn't do this, perhaps it's something simple? Or not, lol. Are there any specific wire harnesses I should check over & test?

Thanks in advance...

wct · March 9, 2007

I have seen a few of the c0281 brake lamp switch codes and usually blow this code off if it is stored in history as a false code. It is possible that the tail light out could of set this code. But I would put this code on the back burner for now and focuse on the c0268 This code could be some what hard to diagnose W/ out a scan tool. You may want to disconnect the batt cables then disconnect the 2 way connector @ ebcm should be black & red wires then preform a total resistance test from the batt cables to the terminals @ ebcm. Should be less than .2 ohms if high then you have a concern and need to address, if good then this is were a scan tool will probably be needed. more unlikely you have a concern w/ ebcm or BPMV. If you get a used one, I would think both should come as a unit. If I remember they are kinda spendy so you want to make sure that is you concern.-WCT

Fortune50 · March 9, 2007

Wow, thanks a bunch for that reply! Do you think this will fix it if the power/ground wiring reads ok (less than .2 ohms)?

http://cgi.ebay.com/ebaymotors/ABS-Module-...0QQcmdZViewItem

If it is "stuck on", which EBCM pins would I need to check for this? BTW, the pump does NOT run all the time.

Fortune50 · March 9, 2007

Also, what is the BPMV?

wct · March 9, 2007

Also, what is the BPMV?

brake pressure modulator valve (BPMV)-The BPMV uses a 3-circuit configuration to control the left front wheel, the right wheel, and the combined rear wheels. the BPMV contains the following components:

-pump motor

-three isolation valves

-three dump valves

-front low pressure accumulator

-rear low pressure accumulator

The EBCM applies the ground needed for pump motor activation. The low side of the pump motor has a feedback circuit to the EBCM. when the pump motor is commanded OFF and @ rest, feedback voltage is high. When the pump motor is winding down after being commanded ON and then OFF, feedback voltage is low. The EBCM monitors this feedback voltage in order to determine if the motor is functioning properly.

Conditions for setting the dtc

The EBCM detects any of the following conditions:

*An open or shorted pump motor

*An open or shorted pump motor driver circuit

*A seized pump motor

So I would check the 60 amp maxi-fuse in the under hood fuse box just to make sure that is ok (I would use a test lamp across the fuse terminals to make sure that power is on both sides.) Then thoroughly inspect connections or circuity that may cause an intermittent malfunction.

If all ok then you will need a scan tool to command the pump on and check for power and grounds @ the pump to see if voltage is @ the pump.

I'm sorry but the EBCM is a (Fred) fabulists remarkable electrical device that I have no idea how it works inside, the schematic doesn't really show how the power gets to the BPMV. C1 @EBCM terminal B red wire is voltage from the 60 amp fuse and terminal A is ground black wire.

So I hope this helps you out. If I had toGUESS [/b]I would say you have a concern W/ the EBCM,BPMV most likely pump issue -WCT

Fortune50 · March 10, 2007

Thanks WCT, that reply ROCKED!!

I guess my options for checking the system for this DTC are slim if the 60 amp fuse is good and if the red & black wires show no resistance, huh? The ABS light only comes on after the truck has moved a few feet after each start up and stays on thereafter BUT always resets after the truck is shut off and restarted and stays off until the truck is moved again. So, I'm guessing it's failing the pump motor circuit during some kind of initialization test. There's no "wiring" to access in order to check to see if the EBCM is getting these voltage changes from high, to low, to high during this initialization test as the unit's "wiring" between the ECBM & pump motor is self-contained and sealed inside the unit, right? If so, then I guess either I try to find someone who has a scanner that can read chassis codes, or have him take it to the dealer and spend $100 I suppose to have it diagnosed...

THANKS AGAIN!

TBLAZER · March 10, 2007

Thanks WCT, that reply ROCKED!!
I guess my options for checking the system for this DTC are slim if the 60 amp fuse is good and if the red & black wires show no resistance, huh? The ABS light only comes on after the truck has moved a few feet after each start up and stays on thereafter BUT always resets after the truck is shut off and restarted and stays off until the truck is moved again. So, I'm guessing it's failing the pump motor circuit during some kind of initialization test. There's no "wiring" to access in order to check to see if the EBCM is getting these voltage changes from high, to low, to high during this initialization test as the unit's "wiring" between the ECBM & pump motor is self-contained and sealed inside the unit, right? If so, then I guess either I try to find someone who has a scanner that can read chassis codes, or have him take it to the dealer and spend $100 I suppose to have it diagnosed...

THANKS AGAIN!

Before you do anything else,make shure the ground for the EBCM is in good condition,the ground is a common problem with this models.

Here is a procedure from a GM bulletin,the trouble codes on this bulletin are not the same as yours but it's still a possible condition.

Also check the ground on the front of the frame,left side,behind the bumper by the front support body mount.

Remove the EBCM Ground. The EBCM Ground is located on the frame beneath the driver's side door. If multiple grounds are found in this location, the EBCM ground can be identified as the heavy (12-gauge) wire.

Clean the area, front and back, using a Whiz Wheel®.

Install the ground, then the washer and then the bolt to the frame.

Fortune50 · March 24, 2007

Well I thought I'd update this page and give some more info. I have contacted a vendor online that rebuilds the ebcm's, They said to test the ABS do the following:

"You can test the pump motor if you unplug the motor from the module (the small connector with red and black wires) and the similar connector supplying power to the module. You can then jump the two connectors together (red to red and black to black) and the motor should run. You can also do this by simply unplugging the motor connector from the module and connecting it to another 12v battery source...If the pump then runs then your module is at fault".

Would this be a viable test of the EBCM to determine if it's bad or if it's the pump motor gone bad instead? Is this a safe test that wouldn't cause harm to the motor or circuit? I haven't had a chance to do anything yet with his truck as he's constantly needing to use it as he's building himself a house, lol.

Also, he needs his rear brakes serviced, the pads are thin, any tips for me in order to do the job right with his Tahoe? It's making a pretty good noise right now, especially when backing up. Is the parking brake separate or part of the caliper? I've done plenty of pad/rotor/caliper/brake line and hose replacements on cars (even on ATVs), but not on Tahoes ...

Also, (sorry) he was told his passenger side front seal is leaking in the front differential. Is that hard to do? I've done a few front cv axles over the years, but not on Tahoes ;).

wct · March 24, 2007

Well I thought I'd update this page and give some more info. I have contacted a vendor online that rebuilds the ebcm's, They said to test the ABS do the following:
"You can test the pump motor if you unplug the motor from the module (the small connector with red and black wires) and the similar connector supplying power to the module. You can then jump the two connectors together (red to red and black to black) and the motor should run. You can also do this by simply unplugging the motor connector from the module and connecting it to another 12v battery source...If the pump then runs then your module is at fault".

Would this be a viable test of the EBCM to determine if it's bad or if it's the pump motor gone bad instead? Is this a safe test that wouldn't cause harm to the motor or circuit? I haven't had a chance to do anything yet with his truck as he's constantly needing to use it as he's building himself a house, lol.

Also, he needs his rear brakes serviced, the pads are thin, any tips for me in order to do the job right with his Tahoe? It's making a pretty good noise right now, especially when backing up. Is the parking brake separate or part of the caliper? I've done plenty of pad/rotor/caliper/brake line and hose replacements on cars (even on ATVs), but not on Tahoes ...

Also, (sorry) he was told his passenger side front seal is leaking in the front differential. Is that hard to do? I've done a few front cv axles over the years, but not on Tahoes ;).

(If you are removing the rotor for resurface or to replace)

Rear brakes aren't to bad to do on a Tahoe, I believe that the caliper bolts are a 18mm and you will probably have to use a wrench, u may get a socket if it's a shallow socket. note: these bolts are usually very tight i think they are loc tighted. these bolts will remove the caliper and mounting to remove the rotor. anther note: the rotors may be hard to remove because the park brake shoes are located inside the drum part of the rotor. I think they call this rotor design a drum in hat. Usually the drums are rusty because no one uses the park brake, you may have to beat on the rotors to get them off gm recommended using a slide hammer with a special tool that fits in the cooling fins. and you may have to rotate the rotor as you beat on it. I would recommend beating on the rotor were the rim mounts to the rotor but be careful not to hit the studs. Now that the rotor is off inspect the shoes they should be ok may want to touch them up w/ some smooth sand paper to remove any glazing and then clean them w/brake clean, then install your rotor and in stall the caliper apply thread locker to the threads then tighten to a 129 ft lbs. "O"ya you will want to clean the axle hub before installing the rotor to prevent lateral run out which could lead to a pulsation. then remove your caliper bolts I think they are 15mm and compress your piston. clean and lube your caliper pins then remove your pads and remove the anti rattle slides if you have new ones w/ your pads and start resembeling then tighten to 31 ft lbs apply thread locker also. you may want to remove caliper first before removing the mounting bracket. THEN MAKE SURE THAT YOU PUMP THE BRAKE PEADLE UNTIL IT GETS HARD!!!!!!! [/b]before you start the engine so you don't end up in the neighbors yard. then check the master cyl for proper fluid level it should be close and shouldn't have to add any but i still check it. Then test drive to burnish in the rotors on a smooth road drive @ 30 mph then firmly press the peddle w/out locking the wheels then let the rotors cool and repeat several times. I hope this makes sense to you If not reply back and I will try to clarify it for you. -WCT the front axle seal may be difficult on the ground.

Fortune50 · March 25, 2007

...-WCT the front axle seal may be difficult on the ground.

Thanks for that reply WCT on the rear brake service. I'll be replacing the pads, not sure about the rotors as I'll need to "mic" them.

Do you think that the axle seal is too difficult w/o a lift? WCT, what is your opinion on "hotwiring" the pump motor to see if it'll work in order to try and find out if the problem is the ebcm or the pump motor (assuming all the wiring checks out and the ground is cleaned up)?

Turnintires · March 25, 2007

perform the TSB for the EBCM ground as TBLAZER said ? this is not an uncommon problem. and also easer to rectify than putting in a rebuilt EBCM (that will potentially do the same thing again if the ground is not checked.

durlacher · June 12, 2007

I have seen a few of the c0281 brake lamp switch codes and usually blow this code off if it is stored in history as a false code. It is possible that the tail light out could of set this code. But I would put this code on the back burner for now and focuse on the c0268 This code could be some what hard to diagnose W/ out a scan tool. You may want to disconnect the batt cables then disconnect the 2 way connector @ ebcm should be black & red wires then preform a total resistance test from the batt cables to the terminals @ ebcm. Should be less than .2 ohms if high then you have a concern and need to address, if good then this is were a scan tool will probably be needed. more unlikely you have a concern w/ ebcm or BPMV. If you get a used one, I would think both should come as a unit. If I remember they are kinda spendy so you want to make sure that is you concern.-WCT

Hi, i'm a GMTC newbie from across the ocean (Europe), with the same problem: ABS light and brake light (amber and red) coming on intermittent, for no obvious reason on my 2001 Tahoe 4wd

Tried the ground cleaning procedure as discribed in the TSB, to no avail.....

Any suggestions? If you guys think replacing an EBCM is expensive where you are, come over to Europe and cry with me....

Mick D.....

Fortune50 · June 15, 2007

Well I performed the TSB to clean the ground, no change. Before doing that I checked with a DMM the volts going to the EBCM at the two wire connector, it showed the exact same voltage as the battery (12.60) volts. So I'm assuming it's not related to a bad ground/wiring to power the unit. Then I also unplugged the motor's two wire connector and "jumped" the EBCM's & motor's two wire connectors together and the motor ran. Does it sound kind've "weak" when it's running?-I don't know what it should sound like, lol. Anyways, there is some kind of test with an ohmmeter when you connect together the two 2 wire connectors at the EBCM I found on this link:

http://i20.ebayimg.com/01/i/01/c6/5f/b4_1.JPG

I wonder if I do this, if it will verify or not that the EBCM is good or bad...

Fortune50 · June 16, 2007

I forgot to add that I also did the rear brakes. The rotors came off fine. Both inside pads were worn, the right side was worse, it had no padding left (toasted the rotor), the left side had about 15%, but still somehow had dug a deep trench into the rotor as the pad had a big bulge in it, weird. The parking shoes looked ok. BTW, does anyone know the torque spec on the lugnuts for an '02 Tahoe 4x4 Z71 w/ 4.10 gears?