Troubleshooting

DTC P1646 TRANSMISSION CONTROL ECU MALFUNCTION*

*: Only for sequential manual transmission vehicle.

CIRCUIT DESCRIPTION

DTC Detection Condition:

The transmission control ECU communicates whether its operation is normal or not to the ECM.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Condition:

Typical Malfunction Thresholds:

If communication between the ECM and the transmission ECU fails, the ECM will illuminate the MIL and set a DTC.

Wiring Diagram:

Step 1 - 2:

Step 3:

INSPECTION PROCEDURE

HINT:
- If DTCs P0860 and P1646 are output simultaneously, the fail-safe function stops the engine. If the engine is stopped, the transmission control system may be abnormal.
- Read freeze frame data using the hand-held tester or the OBD II scan tool, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, this is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.