P03AF: Cylinder 3 Pressure Too High

What it means

Cylinder 3 measured peak combustion pressure is above the calibrated maximum — typically pre-ignition, knock, over-fuelling, or runaway combustion.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

The cylinder 3 pressure sensor lets the engine control module monitor peak combustion pressure. This code sets when cylinder 3 pressure exceeds the calibrated limit, which can indicate abnormal combustion, excessive fueling, or a misleading sensor signal; the engine may enter reduced-power operation.

Common causes

Most likely first.

1. Excessive fueling to cylinder 3
2. Knock or pre-ignition
3. Faulty cylinder 3 pressure sensor
4. Engine control or timing fault

Symptoms

• Check engine light on
• Engine knocking or pinging
• Rough running or misfire
• Reduced power

How to diagnose it

1. Check freeze-frame data and live cylinder 3 pressure, knock, and fueling information to see when the high reading occurs.
2. Inspect the cylinder 3 sensor connector and wiring for damage that could distort the pressure signal.
3. Check for abnormal cylinder 3 injector operation or signs of excessive fueling, comparing available data with the other cylinders.
4. Assess for knock or pre-ignition symptoms and check the engine timing and control data using the manufacturer's procedures.
5. If the wiring and combustion checks do not explain the reading, test the cylinder 3 pressure sensor against the manufacturer's specification.

Common fixes

• Repair damaged cylinder 3 sensor wiring or connector terminals.
• Correct an injector fault causing excessive fueling to cylinder 3.
• Address the confirmed timing or engine-control fault affecting cylinder 3 combustion.
• Replace the cylinder 3 pressure sensor if it fails the manufacturer's test.

Can I keep driving?

Do not continue driving if the engine is knocking, misfiring badly, or has reduced power; stop safely and arrange diagnosis. Excessive combustion pressure can damage the piston, valves, or other engine parts.