P03A5: Cylinder 2 Pressure Too High

What it means

Cylinder 2 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 2 pressure sensor measures combustion pressure for the engine control module. This code sets when cylinder 2's measured peak pressure exceeds the calibrated maximum; the cause may be excessive fueling, abnormal combustion, a faulty sensor, or an engine control problem.

Common causes

Most likely first.

1. Excessive fueling to cylinder 2
2. Knock or pre-ignition
3. Faulty cylinder 2 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 2 pressure readings to establish whether the high value occurs at idle, under load, or during a particular event.
2. Listen for knocking and check for related misfire or fuel-control codes; avoid running the engine under load if abnormal combustion is present.
3. Inspect the cylinder 2 pressure sensor connector and wiring for damage or a signal fault that could create a false high reading.
4. Check cylinder 2 injector operation and fuel-control data for evidence of excess fueling.
5. Compare sensor readings and relevant timing or control data with the manufacturer's specification before concluding that combustion pressure is genuinely excessive.

Common fixes

• Repair damaged cylinder 2 sensor wiring or connector terminals.
• Correct a confirmed cylinder 2 injector fault that is causing excess fueling.
• Replace the cylinder 2 pressure sensor if its signal is faulty and the circuit checks out.
• Repair a confirmed engine control or timing fault causing excessive cylinder 2 pressure.

Can I keep driving?

Do not continue driving if the engine is knocking, running roughly, or has reduced power; stop safely and arrange prompt diagnosis. Excessive cylinder 2 pressure or abnormal combustion can damage the piston, valves, or other engine parts.