Brakes - Anti-lock Brake System Pump Self-Check Noise
NUMBER 12-BR-001GROUP BRAKES
DATE APRIL 2012
MODEL(S) ALL
SUBJECT: ABS PUMP SELF-CHECK NOISE
Description: The Anti-lock Brake System (ABS) performs a hydraulic pump self-check test during the first acceleration after each ignition switch cycle. During this test, the ABS computer tests the pump modulator valves, solenoids, and motor for proper operation. This test occurs at a vehicle speed between 0 and 25 mph for all vehicle models. During this test, a slight noise (which customers may describe as a rattle, groan, growl, gurgling, or buzz) may be heard and a mild vibration may be felt through the brake pedal. The noise and vibration last approximately one second. If any system faults are found, the system disables the anti-lock braking function and will illuminate the ABS warning lamp and set a diagnostic trouble code (DTC).
The purpose of this bulletin is to emphasize that this noise is the result of a normal function self-check test and cannot be eliminated by replacing the Hydraulic Electronic Control Unit (HECU). This bulletin also provides a procedure to confirm the noise is a result of the self-check test using chassis ears.
NOTE
The HECU interactive pump self-diagnostic test and related activation noise does not affect the ABS operation.
Applicable Vehicles
SST Information
NOTE
For information on obtaining special service tools, please contact SPX by calling 1-800-345-2233.
Service Procedure:
Use this procedure to verify that the noise heard comes from the ABS system self-check test.
1. To reproduce the self-check diagnostic noise, start the engine and accelerate the vehicle.
A short "buzz" type noise will be heard between 0 and 25 mph. The noise varies in duration, and can last up to about 1 second.
The noise is very quiet and most of the time will not be noticeable. If it is not heard, shut off the ignition, and continue to step 2 to install chassis ears.
2. To amplify the noise, install a chassis ears clip onto one of the hard lines directly installed onto the HECU.
3. Plug the other end of the clip into the chassis ears control box. Note which port is used (plug is installed into port # 1 on the image shown).
4. Using the selection knob, choose the same port number into which the clip plug was installed (# 1 is selected on the image shown).
Turn the volume knob to power the unit ON. Be sure the volume is turned loud enough to hear the noise clearly.
5. While listening with the chassis ears, start the engine, and accelerate the vehicle to at least 25 mph to hear the self-check pump noise.