P03B1: Cylinder 3 Pressure Variation High

What it means

Cylinder-to-cylinder pressure variation on cylinder 3 is above the calibrated maximum — combustion is unstable cycle-to-cycle, typical of partial misfire or injector seat erosion.

At a glance

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

How it works

The cylinder 3 pressure sensor tracks combustion pressure from cycle to cycle. This code sets when the variation is higher than the calibrated limit, indicating unstable combustion in cylinder 3 or an unreliable pressure signal.

Common causes

Most likely first.

1. Unstable combustion or partial misfire
2. Faulty cylinder 3 pressure sensor
3. Fuel injector fault
4. Low compression in cylinder 3

Symptoms

• Check engine light on
• Rough idle or engine misfire
• Shaking or vibration
• Reduced power

How to diagnose it

1. Record freeze-frame data and compare cylinder 3 pressure variation and misfire counts with the other cylinders.
2. Inspect the cylinder 3 sensor connector and wiring for looseness, corrosion, or damage that could create erratic readings.
3. Check cylinder 3 injector operation and compare its fueling data with other cylinders for signs of inconsistent delivery.
4. Assess cylinder 3 compression against the manufacturer's specification if injector and signal checks do not explain the variation.
5. Test the pressure sensor and verify the signal under the conditions captured in the freeze-frame data.

Common fixes

• Repair a loose, corroded, or damaged cylinder 3 sensor connection.
• Service or replace the cylinder 3 injector if testing confirms inconsistent delivery.
• Repair a compression or valve-sealing problem in cylinder 3.
• Replace the cylinder 3 pressure sensor if its output is faulty.

Can I keep driving?

Avoid hard acceleration and extended driving if the engine is shaking or misfiring. Continued unstable combustion can reduce power, raise emissions, and damage the catalytic converter.