What does it mean?
P1806 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Shift Fork Position Sensor 3 and 4 System (Power supply voltage low range out) .
Symptoms
- MIL (check engine lamp) is on and the transmission enters limp mode
- Gears in the affected group are unavailable, so the vehicle runs on a restricted set of ratios
- Shifts are refused, very slow or extremely harsh
- Clutch or actuator error messages on the dashboard of automated units
- The vehicle may refuse to move at all from a standstill
- The gear indicator shows dashes or an incorrect gear
Likely causes
- Short to ground on the shared supply line, pulling the voltage down for both sensors
- One of the two sensors failed and overloading the supply
- Open circuit or a high-resistance joint in the supply feed from the control unit
- Corroded or water-filled connector at the transmission after washing or driving through water
- Internal transmission harness rubbed through against the housing
- Poor control unit ground or a weak battery reducing the available reference
- Failed supply output inside the control unit
How to fix it
- Check battery condition and charging voltage first, then clean and retighten the control unit grounds
- Measure the supply voltage at each of the two sensor connectors with the ignition on
- Disconnect one sensor at a time and see whether the supply voltage returns to normal
- With the sensors disconnected, check the supply wire for continuity and for a short to ground
- Inspect the transmission connector and internal harness for water, corrosion and chafe damage
- Replace the shorted sensor or repair the wiring, then run the position learn procedure before road testing