U0128 — Lost Communication With Park Brake Control Module

Diagnostic algorithm

1. Record all codes and symptoms. Attempt to communicate with the park brake control module using a capable scan tool; note if the module list shows it as 'not present' or 'no response'.
2. Verify vehicle battery voltage ≥ 12.0 V and good battery connections. Low voltage can cause communication faults.
3. Visually inspect the park brake module and connector for corrosion, bent pins, water intrusion, or damage. Repair or replace connector as needed.
4. Check fuses and power feed to the park brake module. Verify 12V supply at the module pin with ignition ON and a good ground reference.
5. With ignition OFF, measure resistance between CAN_H and CAN_L at a convenient junction — expect ~60 ohms. If open or very high, check for missing termination. If much lower, inspect for parallel short.
6. With ignition ON, measure idle voltages on CAN_H and CAN_L at the module connector; both should sit near ~2.5 V. Use an oscilloscope to look for bus activity and dominant/recessive transitions.
7. If bus voltages are abnormal, isolate sections of the CAN network: disconnect suspect modules (one at a time) to find which device causes the bus problem, or to find the missing terminator.
8. Perform continuity checks between the park brake module CAN pins and the corresponding nodes at the BCM/ABS or gateway to identify opens or shorts. Inspect splices and junction blocks.
9. Repair identified wiring/connectors (repair splice, replace damaged harness), replace blown fuse, and secure grounds. Reconnect and recheck communication.
10. If wiring and power are good but module does not respond, consider replacing or reflashing the park brake control module following OEM programming procedures. Re-scan and clear codes, then road test.
11. After repair, clear all codes and verify normal operation of EPB and related systems. Monitor for return of U0128 or other network DTCs.