ELECTRONIC CONTROL UNIT (ECU) OPERATING TEST
Tools and Special Tools
Tool Kit, General Mechanic's
ECU OPERATING TEST
Apply 12 V dc power to Anti-lock Braking System (ABS).
ECU/dual modulator valve assembly should click four times.
If ABS indicator lamp comes on for three seconds and then goes out, this indicates a proper installation.
Operating Test is complete.
If ABS indication lamp comes on and stays on, check sensor installation by removing power from ABS and
raising sensed wheels so they may be rotated.
Apply emergency air to fill air tanks and release spring brakes so that wheels may be rotated.
Repeat Steps 1 and 2.
Rotate each sensed wheel, one at a time and at a rate of 1/2 revolution per second. This rate equals a
wheel speed of approximately 4 mph (7 km/h). If ABS indicator lamp goes out and stays out, a proper
installation is indicated and Operating Test is complete.
If ABS lamp does not go out, there is a sensor gap problem or hardware fault. Adjust sensor gap and, if
necessary, perform a fault code check (Step 18).
Test sensors at each wheel location by disconnecting power to ECU assembly.