2007 Liberty KJ Factory Service Manual 9 - ENGINE

U0121-LOST COMMUNICATION WITH ANTI-LOCK BRAKE MODULE





For a complete wiring diagram Refer to Section 8W.



Possible Causes
  
DTCS RELATED TO BATTERY VOLTAGE, IGNITION, OR VIN MESSAGES
  
CAN C BUS CIRCUITS OPEN OR SHORTED
  
ABS POWER AND GROUND
  
ABS
  
PCM
  



Diagnostic Test

1. VERIFY DTC IS ACTIVE

NOTE: Ensure the IOD fuse is installed and battery voltage is between 10 and 16 volts before proceeding.


Turn the ignition on.
With the scan tool, select View DTCs.

Is this DTC Active?

Yes


No

2. CHECK FOR ANY OF THE FOLLOWING ACTIVE DTCS

With the scan tool, read all active DTCs from all CAN C Bus modules.

NOTE: Check for CAN C hardware electrical, VIN Missing/Mismatch, battery or ignition related DTCs.



Does the scan tool display any active DTCs to the conditions listed above?

Yes


No

3. VERIFY THAT THE ABS IS ACTIVE ON THE BUS

With the scan tool, select ECU View.
Verify that the ABS is active on the bus.

Is the ABS active on the bus?

Yes


No

4. CHECK FOR ADDITIONAL COMMUNICATION RELATED DTCS

With the scan tool, select Network View and select Advanced.

Is there more than one module with active DTCs “Logged Against” the ABS?

Yes


No