P0604 Fault Code in Land Rover: Causes, Symptoms, and Fixes

The ECU/PCM/TCM runs self-tests on its internal memory. If the RAM (used for temporary calculations and real-time operations) fails or shows corrupted data, this code is triggered. Unlike P0603 (KAM error) which affects stored learned data, P0604 indicates an active hardware/software fault in the controller’s RAM.

Common Causes:

1. Faulty ECU/PCM/TCM (internal RAM failure)
2. Voltage irregularities (weak battery, alternator issues, power surges)
3. Corrupted software or failed module programming
4. Poor grounds or loose electrical connections to the control module
5. Water intrusion or overheating in ECU/TCM

Symptoms:

1. Check Engine Light (CEL) illuminated
2. Engine stalling or hard start
3. Rough shifting (if TCM is affected)
4. Limp mode (reduced power / locked gear)
5. Unstable idle or misfires
6. Sudden drivability issues

Possible Fixes:

1. Check battery & charging system – weak voltage spikes can corrupt RAM.
2. Inspect ECU/TCM connectors – clean and tighten ground/power connections.
3. Check for water/damage near ECU/TCM.
4. Reflash/reprogram ECU/TCM software (if available).
5. If error persists → ECU/TCM hardware failure may require replacement.