P03F8
B Camshaft Position Actuator Position Sensor C Circuit Low Bank 1.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 3
- AreaIgnition system or misfire
- F8
- FaultThe specific fault in that area
What it means
P03F8 means the engine control unit has detected a low voltage or signal on the circuit of position sensor 'C' that monitors the B camshaft position actuator on Bank 1. B camshaft is normally the exhaust camshaft, but this depends on the engine layout and the manufacturer's definition. The control unit saw the sensor signal fall below its expected range, which suggests a short to earth, an open circuit, a supply fault or a failed sensor.
Symptoms
- Engine warning light on
- Rough idle or unstable idle speed
- Reduced power or hesitation under load
- Poor fuel economy
- Hard starting or occasional stalling
- Engine may go into a limited performance mode
Possible causes
- Wiring fault in the sensor circuit, such as a signal wire chafed or shorted to earth, or an open circuitlikely
- Damaged, corroded or loose connector at the actuator position sensor or control unitlikely
- Failed camshaft position actuator position sensorlikely
- Fault in the sensor's reference supply or earth, including a shared supply shorted elsewherepossible
- Fault in the camshaft actuator or phaser assembly that contains the sensor, or oil contamination damaging itpossible
- Low battery or charging voltage upsetting sensor readingsrare
- Internal fault in the engine control unitrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting engine temperature, speed and load when the fault set. Look for other cam timing or sensor supply codes.
- Check the battery and charging voltage, as low voltage can cause false circuit faults.
- Visually inspect the wiring and connector for the Bank 1 sensor and actuator for chafing, oil soaking, heat damage, corrosion and bent or pushed-back pins.
- Check the engine oil level and condition, since oil contamination can affect the actuator and its wiring.
- Using the manufacturer's wiring diagram for the engine, identify which sensor is 'C' and check its supply, earth and signal voltages with the connector fitted and unplugged.
- Test the signal wire for continuity and for a short to earth, and check the supply and earth circuits for resistance.
- Watch live data for the actuator position and its sensor reading while wiggling the harness, to find intermittent faults.
- If the wiring tests good, compare the sensor and actuator against the manufacturer's specifications, as the procedure varies by model and engine.
How to fix
- Repair or replace damaged wiring, and secure the harness away from heat and sharp edges.
- Clean, repair or replace a corroded or damaged connector and its terminals.
- Replace the faulty position sensor or the actuator assembly containing it, following the manufacturer's procedure.
- Restore a faulty supply or earth to the sensor, including any shared circuit shorted elsewhere.
- Correct oil level or oil quality problems that affect the actuator, then clear the codes and confirm the fault does not return.
- Only if a known fault with the control unit software applies to this engine, have the calibration updated by a qualified workshop.
Can I keep driving?
The car can usually be driven carefully for a short time, but book it in soon as the cam timing may be restricted and could affect performance and economy. Stop driving if the engine runs very roughly, stalls or goes into limp mode.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.