What does it mean?
P1657 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Skip Shift 1-4 Upshift Solenoid Control Circuit Malfunction .
Symptoms
- MIL on, usually as the only warning lamp, because only the skip shift function is affected
- The 1-4 forced upshift no longer happens, or it engages permanently so second and third are blocked at light throttle
- Shifter feels blocked when moving out of first gear, or unusually free where it used to resist
- No other drivability change; the engine runs normally
- Readiness monitors incomplete, which can hold up an inspection
Likely causes
- Skip shift solenoid coil open or shorted internally
- Connector at the transmission contaminated with oil, water or corrosion
- Harness chafed against the transmission case or heat damaged near the exhaust
- Open or shorted control wire between the solenoid and the module
- Blown fuse on the solenoid supply feed
- An aftermarket skip shift eliminator left plugged in or wired incorrectly
- Failed output driver in the control module
How to fix it
- Locate the skip shift solenoid on the transmission and inspect its connector for oil wicking, corrosion and heat damage
- Measure the solenoid coil resistance at the connector and compare it with specification
- Check for supply voltage at the connector with the ignition on, and check the related fuse
- Command the solenoid with the scan tool if bi-directional control is available and listen for it actuating
- Test the control wire back to the module for continuity and for shorts to ground and battery voltage
- Remove any aftermarket eliminator device and retest with the original wiring
- Replace the solenoid if it is electrically open or shorted, then clear the code and verify during a light-throttle drive