What does it mean?
P1303 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Implausible Transmission Self-Learning Signal Received .
Symptoms
- MIL (check engine lamp) on together with a transmission warning
- Jerky, harsh or slipping shifts, especially between the lower gears
- Delayed engagement when selecting drive or reverse
- Limp mode with the transmission held in a single gear
- Torque reduction during shifts is wrong, so the engine bogs down or flares between gears
Likely causes
- Adaptation values driven out of range by worn clutches, bands or a slipping torque converter
- Wrong fluid type, wrong level or badly degraded fluid upsetting the shift adaptation
- Corrupted adaptation memory after a low-voltage event or an interrupted programming session
- Software or calibration mismatch between the transmission and engine control modules
- Intermittent bus communication corrupting the message content
- Failed transmission control module
How to fix it
- Check fluid level and condition first; dark or burnt fluid points to internal wear
- Read the stored adaptation values with a capable scan tool and compare them with the acceptable range
- Verify software and calibration compatibility between the two modules
- Inspect the bus wiring and both module connectors for corrosion, chafing and loose pins
- Reset the adaptations and complete the full learning drive cycle at normal operating temperature
- If the values drift out of range again, plan a mechanical inspection of the transmission rather than repeating the reset
- Replace the transmission control module only after fluid, wiring and software have all been proven