What does it mean?
P1655 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: PCM Internal Circuit Malfunction .
Symptoms
- MIL on, often with a scatter of unrelated codes appearing together
- Limp mode with reduced power, or stalling and failure to restart
- Intermittent loss of communication with the scan tool
- Relays, fans or the fuel pump behaving randomly, including the fan running after key-off
- Rough idle and poor shift quality after every restart because adaptations are lost
Likely causes
- Unstable supply voltage from a weak battery, a failing alternator or an incorrect jump start
- Loose or corroded PCM power feeds and ground connections
- Water ingress into the PCM connector or case, often from a blocked cowl drain
- An external short on a controlled output that damaged an internal driver
- Interrupted or failed software reflash
- Voltage spike from welding on the vehicle without disconnecting the battery
- Genuine internal failure of the module's processor or driver circuitry
How to fix it
- Load-test the battery and check the charging system before condemning the module
- Clean and tighten the PCM grounds and the main engine and body grounds, then confirm with voltage-drop tests
- Unplug the PCM and inspect the connectors and case for moisture, corrosion and pushed-out pins
- Check controlled outputs (solenoids, relays) for shorts that could damage a driver, measuring coil resistance on each
- Look for a manufacturer software update or reflash for this module
- Clear the code and run a full drive cycle to confirm whether the fault is active or historic
- Replace and program the PCM as the final step, after every supply-side and external short check