What does it mean?
P1680 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Powertrain Control Module Internal Malfunction .
Symptoms
- MIL on, often with a group of unrelated codes appearing at the same time
- Reduced power or limp mode; in worse cases stalling, long cranking or a no-start
- Scan tool communication drops out intermittently
- Relays and fans switching randomly, including a cooling fan that runs after key-off
- Rough idle and poor shift quality after every restart because learned values are lost
Likely causes
- Low or unstable supply voltage from a weak battery or a failing alternator
- Corroded or loose module power feeds and ground connections
- Water intrusion into the module connector or case, often through a blocked cowl drain
- An external short on a controlled output that damaged internal circuitry
- Failed or interrupted software flash leaving the module in an unstable state
- Damage from incorrect jump starting, reversed polarity or welding on the vehicle
- Genuine internal hardware failure of the module
How to fix it
- Load-test the battery and measure charging output before doing anything else; supply faults set this code frequently
- Clean and tighten the module grounds and the main engine and body ground straps, then verify with voltage-drop tests
- Disconnect the module and inspect the connectors and case for moisture, corrosion and pushed-out pins
- Measure the coil resistance of the solenoids and relays the module drives to rule out an external short
- Check for a manufacturer software update or reflash that addresses this fault
- Clear the code and run a full drive cycle to establish whether the fault is active or historic
- Replace and program the module as the final step, once every supply-side and external check is clean