Vehicle: 2010 Chevy Equinox, AWD, L4-2.4L

Mileage: 96,002

Problem: This vehicle was towed in because the power steering was working one day, and when the owner got in to drive it the next morning, the power steering didn’t work.

Details: The technician connected a scan tool to check for diagnostic trouble codes (DTCs). He found two active data communication codes. One is stored in the transmission control module (TCM), the other in the body control module (BCM).

U0121 - (TCM) NO COMMUNICATION WITH ELECTRONIC BRAKE CONTROL MODULE
U0131 - (BCM) NO COMMUNICATION WTH POWER STEERING CONTROL MODULE

Since the technician didn’t have a lot of experience with “U” codes, he called ALLDATA Tech-Assist for some advice and guidance.

The Tech-Assist consultant suggested first checking the fuses, power and grounds at the power steering control module. Then he advised checking for good communication lines to and from the module by load testing those circuits.

The testing verified that all power and grounds were good at the module but there was no voltage on the “serial data communication enable” (wake-up) circuit. In the colored wiring diagram, it’s the LT/BLU wire (circuit 5986 from BCM to the ABS module pin #8 or power steering module pin #1). The BCM uses this circuit to wake up those modules. NOTE: Splice J311 is the common link between the two DTCs.

The tech found splice J311 corroded under the driver sill plate, located on the driver side just where the driver put his left foot.

Confirmed Repair: He repaired the splice, and communication was restored. After clearing both the DTCs, he test-drove the vehicle. All issues are resolved and the DTCs did not return!