ABS and Brakelight
2001 K2500. ABS and Brake light are on before I start moving. Sensors at the front wheels check ok with multi meter ohm and voltage test. No diagnostic codes that I can find with parts store OBDII scanner. Brakes work fine, just no anti-locks. Fuses check fine. Checking connections at the unit under the drivers seat. Don't know the abbreviation for it. At the front there is a two wire connection, easy to remove. at the rear, there is a connector with a little red tab. Before I tear it up, how do you disconnect that connector? Somewhere on here I know i have read what multimeter readings I should get at this unit, can someone point me to that thread? Thank you
As long as your ABS light is on, you will not have your anti-lock brakes working. It's the ABS unit that actually does the anti-lock braking. Fix the ABS problem, the anti-lock brakes work just as before.
Your codes will held diagnos your problems.
I suspect a C**** code.
Did you give your front wheel bearing a test?
Maybe (heymccall) will chime in.
Post #6 is your symptom
Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.
The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.
Measure AC voltage and clean the wheel speed sensor mounting surfaces.
Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual.
Disconnect both the front wheel speed sensor connectors at the frame and harness.
Place a Digital Volt Meter (DVM) across the terminals of each wheel speed sensor connector.
Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
Plug the wheel speed sensor bore in order to prevent debris from falling into the hub during service.
Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, scotch brite, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.
Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor.
Apply (spray) two thin coats of the specified rust penetrating lubricant (corrosion inhibitor) to the complete sensor mounting surface on the bearing hub. Allow to dry for 3-5 minutes between coats. Use ONLY Rust Penetrating Lubricant, P/N 89022217 (in Canada, P/N 89022218).
When the corrosion inhibitor is dry to the touch (about 10 minutes), apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (in Canada, P/N 993037).
Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's.
I hav found that my local O'Reilly store does read c* codes and B* codes, so does Autozone, and Advance Autoparts. This doesn't mean that ALL shops, even those under these umbrella's, will read those codes, so ASK your local location if they will, don't assume they won't. In my locale, both O'Reilly and Advance have very nice Bosch scanners, not remembering what Autozone had.
Cleaned the ground wire under the drivers seat, and a couple of others under the hood. No change. No movement when rocking the tire top to bottom, a tiny amount when rocked front to back, but it looks like might be inner tie rod ends. New O'Reilly's in town I will stop in and see if they use a better scanner. P codes are performance codes, what are C and B codes? On RVn4me's post in the second hyperlink, there is another hyperlink from lyn1130 that tells of cleaning the contacts on the EBCM. can that be done without removal from the rest of the unit, or without removing the entire assembly from the frame of the truck? I have never had much success with rusty brake lines.
More than you ever wanted to know about about OBDII codes: https://www.troublecodes.net/bcodes/
As for the EBCM, I would start by carefully checking/cleaning all of the wiring connectors/connections from/to the EBCM. Coat the cleaned connections with dielectric grease to help prevent future problems.
A bizarre one, but are you hanging a bunch of keys from the ignition? This happened to me once. I took all the keys off (except for the one ignition key) and the ABS, Brake light and "Service Brake System Soon" warning in the DIC went off.
see your from illinois,
After working on a free to me 2002 avalanche from up there. I would replace the wheel bearings, all rotors, pads and calipers. mine was so rusty and corroded everywhere the abs light was on and when you would hit the brakes it would activate every time.
I had to lol when I first test drove it to diagnose it for engineer here at work that ended up giving it to me because dealer would only give him 200.00 as trade in.
plan on replacing metal brake lines too if you have not already.
Since ABS light is active before ever driving, the self test has failed. Self test failures are an open or shorted sensor or its wiring, poor supply voltage or ground, or internal EBCM failure.
You can guess all day long, but, having the fault code will save you a tremendous amount of time in narrowing down what to inspect/ test/ replace.
Been away for a while with work. Got codes C0265 and C0227 so it looks like I will be pulling the control module when the weather warms up. I will try to just remove the module from the motor, but the amount of rust I am finding underneath is not good. Does a replacement module have to be reflashed? How hard is it to replace the brake lines connected to this thing? I am thinking I may have to drop the motor replace the module, and if I go to that much trouble I should replace the rusty brake lines. Thank you to all that are responding.
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