Need help with '02 Tahoe with ABS light on!

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 to anyone who can assist...

Well I thought I'd update this to mention that I've been in contact with a GM tech on another site and it appears I can only check power & ground at the EBCM, any other checks (other than physical) can only be down with a scanner that reads ABS information... .

when did he take it in for the recall? Im having the same issue and they told me the recall was closed:confused2:
We dont have a abs light on but they kick on at low speeds..alot. Making my wife mad to where she dont want to drive it till its fixed.

smokestack said:

when did he take it in for the recall? Im having the same issue and they told me the recall was closed:confused2:
We dont have a abs light on but they kick on at low speeds..alot. Making my wife mad to where she dont want to drive it till its fixed.

Click to expand...

He had the recall done early last March '07.
His specific recall that was performed was listed for ONLY these models:

CHEVROLET / AVALANCHE 2002

CHEVROLET / SILVERADO 1999-2002

CHEVROLET / SUBURBAN 2000-2002

CHEVROLET / TAHOE 2000-2002

GMC / SIERRA 1999-2002

GMC / YUKON 2000-2002

GMC / YUKON XL 2000-2002

I'd go here:
http://www-odi.nhtsa.dot.gov/cars/problems/recalls/recallsearch.cfm
Then enter your vehicle's information and see if there are any recalls listed for it. Also, you may contact Chevy at 1-800-630-2438 or GMC AT 1-866-996-9463.

Awsome, Thanks for the reply. I have a 2000 tahoe so it should be covered. Thanks again for the website

Couple comments here:

One, if you have an Advanced Auto Parts or Autozone nearby, they will let you use their OBD scanner tool for FREE!!! Once I've pulled the code, I'll go back and Google it to see what I come up with.

You'll find websites like this... that are little helpful, but don't really give you a real definitive answer or what to look for.

http://www.obd-codes.com/trouble_codes/obd-ii-c-chassis-codes.php

In your case, the C0281 is the Brake Switch Circuit. If you got an "in" with any of the service advisors or techs at GM in your area, I bet they could lead in you a better direction. If you're the DIY type, you might consider picking up a factory service manual as well.

Hope this helps!

Dano

dano said:

Couple comments here:

One, if you have an Advanced Auto Parts or Autozone nearby, they will let you use their OBD scanner tool for FREE!!! Once I've pulled the code, I'll go back and Google it to see what I come up with.

You'll find websites like this... that are little helpful, but don't really give you a real definitive answer or what to look for.

http://www.obd-codes.com/trouble_codes/obd-ii-c-chassis-codes.php

In your case, the C0281 is the Brake Switch Circuit. If you got an "in" with any of the service advisors or techs at GM in your area, I bet they could lead in you a better direction. If you're the DIY type, you might consider picking up a factory service manual as well.

Hope this helps!

Dano

Click to expand...

Wow, I forgot about this thread. I did buy a factory manual, but for my '01 Sierra 2500HD, but I'm sure '02's are much the same. It does give a diagnostic procedure on each code. But I do not have a Tech II scanner, which is required in order to not only read "chassis" codes-which are codes that start with a C, but to initiate the required ABS tests as well. Auto parts stores around my area only have basic code readers which can only check for PCM stored codes (codes that start with a P) and those are unable to check for any other types of codes.

Oh and about those codes, I learned the C0281 was due to a burned out taillight. If the lights were good, then that code directs toward the stoplight switch and related circuit.
The other code, C0268, is the serious one. It relates to the ECBM's ability to detect whether the BMPV's pump motor is functioning or not during an initialization test it performs on the ABS system after everytime the truck is started and begins moving and then reaches 4mph or more. I did perform some tests relating to see if the EBCM was getting proper power & ground, it was. Just in case, I performed a TSB which calls for the ground to the EBCM to be cleaned up, which I did, no change. Then I "hotwired" the pump motor itself which bypassed it from EBCM control to see if it was working. It was, but it sounded a bit "rough" so I'm suspicious that it's weak and not spinning fast enough in order for the ECBM to read the required feedback voltage from it after it disconnects power to it. I forgot to perform an ohmmeter test on the pump motor, it has a very strict range of 0.3 to 1.0 ohm. If it is out of this range, if less than 0.3, then there's a direct short to ground, if more than 1.0 ohm, than there's high resistance in the motor circuit. Either way, if out of range, the manual says to replace both the EBCM & the BMPV. The reason is if the BMPV motor circuit is out of range, it can easily damage the ECBM's BMPV motor driver circuit apparently. Either way it will be ridiculously expensive to fix this problem! So my buddy has passed on it since he has just built a new house, and has other priorities...hope this info helps out others.

Does the abs act up at slow speeds ? under 10mph if so this could be a bad sensor at the hub, easy fix is replace the bearing/hub assembly. wouldnt hurt with any truck at 70k or more.

Document ID# 742343
2002 Chevrolet Tahoe - 4WD


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DTC C0267 or C0268 and C067 or C068
Circuit Description
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 at 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 Running the DTC
The ignition is ON.
The vehicle speed is greater than 6 km/h (4 mph).
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
Action Taken When the DTC Sets
If equipped, the following actions may occur:

The EBCM disables the ABS/TCS/VSES.
The ABS indicator turns ON.
The traction off indicator turns ON.
The message center displays the SERVICE STABILITY SYSTEM message.
Conditions for Clearing the DTC
The conditions for setting the DTC are no longer present and you use the scan tool Clear DTCs function.

Diagnostic Aids
Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to the following:

• Testing for Electrical Intermittents

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs

• Connector Repairs

Test Description
The numbers below refer to the step numbers on the diagnostic table.

It is imperative that the vehicle be driven to attempt to reset the DTC. Using the scan tool to perform a function test may not produce the same result, and therefore may cause misdiagnosis of the vehicle.

This step tests if the EBCM is capable of activating the ABS pump motor.

A shorted ABS pump motor may damage the EBCM. It is imperative that the steps in the table be followed in order to prevent damage to a replacement EBCM.

Step
Action
Values
Yes
No

Schematic Reference: ABS Schematics

Connector End View Reference: ABS Connector End Views

1
Did you perform the ABS Diagnostic System Check?
--
Go to Step 2
Go to Diagnostic System Check - ABS

2
Use a scan tool in order to clear the DTCs.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does DTC C0267 set?
--
Go to Step 6
Go to Step 3

3
Does DTC C0268 set?
--
Go to Step 4
Go to Diagnostic Aids

4
Turn OFF the ignition.
Disconnect from the EBCM, the 2-way harness connector which contains the battery positive voltage circuit and the ground circuit.
Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

Disconnect the negative battery cable.
Disconnect the positive battery cable.
Place one lead of a DMM on the positive battery cable where the cable normally connects to the battery.
Place the other lead on the battery positive voltage circuit terminal within the 2-way EBCM harness connector.
Measure the total resistance between the positive battery cable and the EBCM.
Does the resistance measure within the specified range?
0.0-0.2 ohms
Go to Step 5
Go to Step 10

5
Use a DMM to measure the resistance of the ground circuit.

Does the resistance measure within the specified range?
0.0-0.2 ohms
Go to Step 7
Go to Step 11

6

Important
On some applications, it may be necessary to separate the EBCM from the BPMV in order to perform this test. Also, DTC C0268 may set when this test is performed.


Turn OFF the ignition.
Disconnect from the EBCM, the ABS pump motor pigtail connector. For systems which have no pump motor pigtail, it is necessary to separate the EBCM from the BPMV in order to gain access to the pump motor connector of the EBCM. Refer to Electronic Brake Control Module (EBCM) Replacement .
Use a connector adapter test kit in order to connect a test lamp between the ABS pump motor power and ground circuits at the pump motor connector of the EBCM.
Turn ON the ignition.
Use the scan tool in order to clear the DTCs.
Use the scan tool in order to perform an ABS Function Test.
Does DTC C0267 set?
--
Go to Step 12
Go to Step 9

7

Important
On some applications, it may be necessary to separate the EBCM from the BPMV in order to perform this test. Also, DTC C0268 may set when this test is performed.


Reconnect both battery cables.
Disconnect from the EBCM, the ABS pump motor pigtail connector. For systems which have no pump motor pigtail, it is necessary to separate the EBCM from the BPMV in order to gain access to the pump motor connector of the EBCM. Refer to Electronic Brake Control Module (EBCM) Replacement .
Use a connector adapter test kit in order to connect a test lamp between the ABS pump motor power and ground circuits at the pump motor connector of the EBCM.
Turn ON the ignition.
Use the scan tool in order to clear the DTCs.
Use the scan tool in order to perform an ABS Function Test.
Does the test lamp illuminate and then turn OFF when the Function Test is performed?
--
Go to Step 13
Go to Step 8

8
Use a DMM in order to measure the resistance across the ABS pump motor.

Does the resistance measure within the specified range?
0.3-1.0 ohms
Go to Step 12
Go to Step 14

9
Inspect for poor connections at the pump motor pigtail connector. Refer to Testing for Intermittent and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 15
Go to Step 13

10
Repair the high resistance in the underhood electrical center or the battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
--
Go to Step 15
--

11
Repair the high resistance in the ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
--
Go to Step 15
--

12

Important
Following EBCM replacement, use the scan tool to perform the Tire Size Calibration procedure and the Trim Level Calibration procedure, if applicable.


Replace the EBCM. Refer to Electronic Brake Control Module (EBCM) Replacement .

Did you complete the replacement?
--
Go to Step 15
--

13
Replace the BPMV. Refer to Brake Pressure Modulator Valve (BPMV) Replacement .

Did you complete the replacement?
--
Go to Step 15
--

14

Important
Following EBCM replacement, use the scan tool perform the Tire Size Calibration procedure and the Trim Level Calibration procedure, if applicable.


Replace the EBCM and the BPMV. Refer to Electronic Brake Control Module (EBCM) Replacement and to Brake Pressure Modulator Valve (BPMV) Replacement .

Did you complete the replacements?
--
Go to Step 15
--

15
Use a scan tool in order to clear the DTCs.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?
--
Go to Step 3
System OK



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Document ID# 742343
2002 Chevrolet Tahoe - 4WD

I had the same problem on my tahoe but its older 1996 2 door tahoe 4X4 the problem it had was the abs sensor I bought the front set on ebay for pennies $25