P03C8

What it means

P03C8 is a generic code meaning the engine control unit has found the signal from the cylinder 6 pressure sensor to be out of its expected range or implausible. The in-cylinder pressure sensor reports combustion pressure, and the control unit compares its output with expected values, with other cylinders or with crankshaft-derived data. The signal did not make sense, so the fault was stored. This sensor is only fitted to certain engines, so the exact test depends on the model.

Symptoms

• Engine warning light on
• Rough running or uneven idle
• Misfire on cylinder 6 or poor combustion quality
• Reduced power or the engine running in a limp mode
• Poor fuel economy
• Hesitation or uneven response under load

Possible causes

• Wiring or connector fault in the cylinder 6 pressure sensor circuit (chafing, corrosion, poor pin tension, water ingress)likely
• Faulty or drifting cylinder 6 pressure sensorlikely
• Carbon build-up or contamination at the sensor tip or in its mounting portpossible
• Real combustion or mechanical problem in cylinder 6 (low compression, misfire, injector or ignition fault) causing a genuinely abnormal readingpossible
• Poor sensor supply voltage or ground, or a fault in the shared reference circuitpossible
• Engine control unit fault or outdated calibration, where the manufacturer has a known issuerare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting engine speed, load and temperature when it set, and check for other cylinder pressure, misfire or sensor supply codes.
2. Check for manufacturer service bulletins or known software updates for this engine, as the sensor fitment and test method vary by model.
3. Inspect the wiring and connector for cylinder 6 pressure sensor for damage, corrosion, moisture, heat damage and loose pins.
4. Check the sensor supply, reference and ground at the connector against the manufacturer's specification.
5. View live data for cylinder 6 pressure and compare it with the other cylinders at idle and under light load.
6. Check for misfire counters on cylinder 6 and inspect the spark plug or injector on that cylinder.
7. If the signal looks wrong but the engine runs well, test the sensor against specification and inspect it for contamination.
8. If the readings suggest a real problem, carry out a compression or leak-down test on cylinder 6.

How to fix

• Repair or replace damaged wiring, terminals or the connector in the sensor circuit.
• Replace the cylinder 6 pressure sensor if it fails testing, following the correct torque and fitting procedure for the engine.
• Clean or clear contamination from the sensor port only where the manufacturer allows it, otherwise replace the sensor.
• Repair the underlying cylinder 6 ignition, fuelling or mechanical fault if it is the cause.
• Update the engine control unit calibration only if an outdated or faulty calibration is a known cause for this engine.
• Clear the code after the repair and road test to confirm it does not return.

Can I keep driving?

Nearby codes

• P03C7GenericCylinder 6 Pressure Sensor Circuit
• P03C9GenericCylinder 6 Pressure Sensor Circuit Low