What does it mean?
P1807 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Shift Fork Position Sensor 3 and 4 System (Power supply voltage high range out) .
Symptoms
- MIL (check engine lamp) is on and the transmission goes into limp mode
- The vehicle will not shift or holds only one gear
- Refused engagement and clutch or actuator warnings on automated units
- The gear display shows dashes
- Other electrical faults may be present if the charging system is overcharging
- The vehicle may be undrivable in the worst case
Likely causes
- Sensor supply line shorted to battery voltage or to a switched power circuit through damaged insulation
- Charging system overvoltage from a failed voltage regulator
- Water or corrosion inside the transmission connector bridging the supply pin to an adjacent power circuit
- A failed sensor feeding voltage back onto the shared supply line
- Damage from an incorrect jump start or a previous harness repair
- Chafed loom where the supply wire touches a permanently live feed
- Failed reference or regulator output inside the control unit
How to fix it
- Measure charging voltage at the battery at idle and at raised engine speed; correct any overcharge first
- Measure the sensor supply voltage at each sensor connector with the ignition on
- Disconnect the sensors and see whether the voltage stays high, which points at wiring or the control unit rather than a sensor
- With the control unit disconnected as well, check the supply wire for a short to battery voltage
- Inspect the transmission connector for water, corrosion and bridged terminals
- Repair the wiring or replace the faulty sensor, then relearn the shift fork positions and road test