What does it mean?
P1664 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Skip Shift 1-4 Upshift Lamp Control Circuit Malfunction .
Symptoms
- The upshift indicator never lights during light-throttle first gear operation
- Or it stays illuminated continuously in every gear
- MIL on while the skip shift solenoid itself may still operate normally
- No change in engine performance or shift feel
- Other cluster lamps may be dim or dead if a shared feed is at fault
Likely causes
- Upshift indicator bulb or LED in the cluster burnt out or removed
- Open or shorted control wire between the control module and the cluster
- Corroded or loose cluster connector terminals
- Internal failure of the cluster indicator driver
- Failed output driver in the control module
- An aftermarket skip shift eliminator interfering with the lamp circuit
- Blown instrument panel fuse
How to fix it
- Verify the lamp during the ignition-on bulb check and again during a light-throttle 1-2 shift
- Check the instrument panel fuse and the cluster power and ground feeds
- Unplug the cluster connector and inspect for bent, corroded or loose terminals
- Test the lamp control wire from the module to the cluster for continuity and for shorts to ground and battery voltage
- Remove any aftermarket skip shift eliminator device and retest with the original wiring
- Replace the bulb or repair the cluster indicator circuit
- Consider the module output driver only once the bulb, cluster and wiring are proven good