Engine

P03A1 — Cylinder 2 Pressure Sensor Circuit Low

Severity: medium Drive with care, to a shop

What P03A1 means

The engine control module reads the cylinder 2 pressure sensor to monitor combustion, fine-tune ignition timing and detect misfires. P03A1 sets when the signal voltage in this circuit falls below the expected range. The cause is usually the sensor itself or a wiring problem such as an open or a short to ground, and rarely the ECM.

Symptoms

  • Check engine light on
  • Rough idle
  • Misfire symptoms or engine shaking
  • Reduced power and sluggish throttle response
  • Possible drop in fuel economy

Possible causes

  1. Failed cylinder 2 pressure sensor
  2. Damaged wiring: open circuit, chafed insulation or short to ground
  3. Corroded, loose or oil-soaked connector
  4. Faulty engine control module (uncommon)
  5. Mechanical problem in cylinder 2 such as rings, piston or valve (uncommon)

How to diagnose

  1. Scan all codes and freeze frame data and look for related misfire codes
  2. Inspect the cylinder 2 sensor harness and connector for damage, corrosion, oil and moisture
  3. Check power, ground and reference voltage at the sensor connector using the factory wiring diagram
  4. Test the signal wire for opens and shorts to ground back to the ECM
  5. View the sensor reading in live data and compare it with the other cylinders
  6. Run a compression test on cylinder 2 if a mechanical fault is suspected
  7. Check engine oil level and condition
  8. If wiring and sensor test good, evaluate the ECM and consider reflashing or replacement

Common fixes

  • Replace the cylinder 2 pressure sensor
  • Repair or replace damaged wiring and the connector
  • Clean the connector terminals and fix the source of oil or moisture
  • Repair cylinder 2 if a mechanical fault is confirmed
  • Replace or reprogram the ECM if everything else checks out

Questions and answers

What does P03A1 mean?

It means the cylinder 2 pressure sensor circuit is giving a low signal. The ECM sees a voltage below normal, most often due to the sensor or its wiring.

Can I drive with P03A1?

Only for a short distance, such as to a shop. If the engine misfires, shakes or the check engine light flashes, stop driving to protect the catalytic converter.

Where should I start diagnosing P03A1?

Start by inspecting the wiring and connector at the cylinder 2 sensor, then test power, ground and signal with a multimeter. Replace the sensor only after the circuit checks out.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.