What does it mean?
U1205 is a Network (CAN bus, module communications) fault code. It indicates: IMA-CAN Malfunction Powertrain Control Module (PCM)Motor Control Module (MCM) .
Symptoms
- Hybrid system warning lamp and the check engine lamp illuminated
- No electric assist and no regenerative braking; the car drives on the engine alone
- Noticeably weaker acceleration and worse fuel consumption
- Assist and charge gauge frozen or blank
- Auto stop-start disabled, the engine keeps idling at every stop
- Scan tool cannot reach the motor control module
Likely causes
- Damaged, chafed or corroded CAN wiring between the PCM and the motor control module
- High resistance or loose terminals at the module connectors, often after body repair or battery service
- Bus wire shorted to ground or to battery positive, or a failed terminating resistor
- Weak 12 V auxiliary battery or a poor module ground causing the motor control module to reset
- Internal failure of the motor control module or its power stage after a high-voltage system fault
- Aftermarket electrical accessories spliced into the CAN or supply circuits
- Outdated or corrupted module software after an interrupted programming session
How to fix it
- Scan every module and note which ones are unreachable; a whole missing branch points to wiring, one missing module points to that unit
- Check the 12 V auxiliary battery state of charge and test the module grounds for voltage drop
- With the ignition off, measure resistance across CAN high and CAN low at the diagnostic connector; roughly 60 ohms means both terminating resistors are present
- Inspect the harness between the engine bay and the hybrid components for rub-through, rodent damage and moisture in connectors
- Wiggle-test the connectors while watching live data for dropouts
- Repair damaged bus wiring with soldered and sealed joints
- Reflash or replace the motor control module only after wiring, supply and ground test good