Anti-lock brake system codes are usually reliable at pointing to the component at fault, but not always. You should always follow the complete diagnostics to fix it right the first time. Follow this Real Fix to see how a code P0040 on this 2007 Buick Terraza was diagnosed and the component that caused the problem.
Vehicle
2007 Buick Terraza CX 3.9
Title
C0040, Replaced Anti-Lock Brake Traction Control Module
Complaint
The customer states the anti-lock brake system (ABS) light is on.
Cause
Connected a scan tool and found code C0040 – Right Front Wheel Speed Sensor Circuit Malfunction. With the scan tool connected, cleared the codes, performed a road test, monitored the ABS wheel speed sensors and found the signal parameter from the right front ABS wheel speed sensor was not present. Raised the vehicle on a lift and inspected the right front ABS wheel speed sensor connector, terminals and wiring harness and found no faults. Key on, back-probed the right front ABS wheel speed sensor signal wire with a lab scope. As the wheel RPM increases frequency (HZ) should also increase with no dropouts or glitches during the test. The right front ABS wheel speed sensor did not produce an observable signal or waveform when monitored with the lab scope. Key on, right front ABS wheel speed sensor disconnected, used a multi-meter to measure the 12 Volt supply and less than 100 mV ground at the connector and found the 12 Volt supply was not present. Key on, back-probed the anti-lock brake traction control module with the multi-meter to measure the specified 12 Volt supply at terminal “9” for the right front ABS wheel speed sensor and found the 12 Volt supply was not present. Back-probed the anti-lock brake traction control module terminal “46” for the 12 Volt supply and terminal “1” ground and found both were present. The results of these tests verified the anti-lock brake traction control module was faulty.
Correction
Replaced the anti-lock brake traction control module, cleared codes, performed a road test and verified the vehicle operated properly. The ABS light did not illuminate and no fault codes returned.
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