P03E3: Cylinder 8 Pressure Variation High

What it means

Cylinder-to-cylinder pressure variation on cylinder 8 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 ECM uses the cylinder 8 pressure sensor to track combustion from one cycle to the next. This code sets when cylinder 8 pressure varies more than the calibrated maximum, which can point to unstable combustion, an injector delivery problem, an ignition fault, or a faulty pressure signal.

Common causes

Most likely first.

1. Cylinder 8 combustion instability or misfire
2. Cylinder 8 injector delivery problem
3. Cylinder 8 ignition fault
4. Cylinder 8 pressure sensor or signal fault

Symptoms

• Check engine light on
• Engine misfire or rough running
• Hesitation
• Reduced power

How to diagnose it

1. Save freeze-frame data and check cylinder 8 pressure variation live data alongside misfire counts and engine speed.
2. Inspect the cylinder 8 pressure sensor connector and harness for loose terminals, chafing, or intermittent contact.
3. Check cylinder 8 ignition components and wiring for damage or a connection fault that could cause an intermittent misfire.
4. Test cylinder 8 injector operation and compare its delivery with the manufacturer's specification.
5. If combustion and fuel checks are satisfactory, test the cylinder 8 pressure sensor and signal circuit.

Common fixes

• Repair a loose or damaged cylinder 8 sensor, injector, or ignition connection identified during inspection.
• Repair the cylinder 8 ignition fault if testing confirms misfire from that system.
• Correct a confirmed cylinder 8 injector delivery problem.
• Replace the cylinder 8 pressure sensor if its signal is faulty with sound wiring.

Can I keep driving?

Keep driving to a minimum if the engine is misfiring or hesitating, and avoid hard acceleration. Continued misfire can increase emissions and damage the catalytic converter; stop if roughness or power loss becomes severe.