P03B2: Cylinder 3 Combustion Performance

What it means

The closed-loop combustion controller reports that combustion performance on cylinder 3 is below the calibrated quality metric. Computed from the cylinder pressure trace — IMEP (indicated mean effective pressure), CA50 (50% mass burnt angle) or peak pressure deviates from the model.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The engine control system evaluates cylinder 3 combustion from its pressure trace, including measures such as pressure development and combustion timing. This code sets when cylinder 3's calculated combustion performance falls outside the calibrated quality range; injector delivery or incorrect data communication can contribute.

Common causes

Most likely first.

1. Injector flow rate drift
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Check engine light on
• Rough running or engine misfire
• Reduced power
• Uneven acceleration

How to diagnose it

1. Use freeze-frame data and live cylinder-specific combustion values to identify which cylinder 3 pressure or performance measure is out of range.
2. Check cylinder 3 injector operation and compare its flow or correction data with the other cylinders.
3. Inspect the cylinder 3 pressure sensor connection and wiring, then confirm that its trace is plausible.
4. Check for related communication or gateway faults and review whether other modules report missing or inconsistent engine data.
5. If communication and sensor data are sound, follow the manufacturer's procedure to evaluate cylinder 3 combustion timing and injector delivery.

Common fixes

• Correct a cylinder 3 injector flow problem confirmed by testing.
• Repair the cylinder 3 pressure sensor connection or wiring if its trace is unreliable.
• Repair a confirmed network wiring or gateway routing fault affecting engine data.
• Replace a faulty pressure sensor or control module only after the manufacturer's tests identify it.

Can I keep driving?

If the engine runs smoothly, keep driving limited and avoid heavy acceleration until diagnosed. A persistent cylinder 3 combustion fault can worsen misfiring, power loss, fuel use, and emissions.