Engine

P03AD — Cylinder 3 Pressure Sensor Circuit Intermittent/Erratic

Severity: medium Drive with care, to a shop

What P03AD means

P03AD means the engine control module is getting an intermittent, jumpy or implausible signal from the cylinder 3 pressure sensor. This sensor measures combustion pressure and helps the ECM monitor combustion, ignition timing and misfires. When the signal drops out or becomes noisy, the ECM can't trust it and sets the code.

Symptoms

  • Check Engine light on
  • Rough idle or engine vibration
  • Hesitation or stumbling under acceleration
  • Feeling of misfires
  • Reduced power
  • Worse fuel economy

Possible causes

  1. Failed cylinder 3 pressure sensor
  2. Damaged wiring harness: open, chafed or shorted wires
  3. Corroded or loose sensor connector
  4. Poor ground or sensor supply problem
  5. Mechanical problem in cylinder 3 (compression, valves, rings)
  6. Rarely, an ECM fault

How to diagnose

  1. Scan all codes and freeze frame data, and look for cylinder 3 misfire codes
  2. Inspect the sensor connector and harness for oil, moisture, corrosion or chafing
  3. Wiggle the harness with the engine running while watching the sensor signal on a scan tool
  4. Check supply, ground and reference voltage at the connector using the factory wiring diagram
  5. Test wire continuity and resistance between the sensor and the ECM
  6. Compare the cylinder 3 signal with the other cylinders
  7. If the signal looks real, check compression and the spark plug or injector on cylinder 3
  8. Clear the code and road test after repair

Common fixes

  • Clean or replace the sensor connector
  • Repair or replace the damaged wiring harness
  • Replace the cylinder 3 pressure sensor
  • Repair any confirmed mechanical engine fault
  • Update software or replace the ECM only after everything else is ruled out

Questions and answers

What does P03AD mean?

It is a circuit fault for the cylinder 3 pressure sensor, with an intermittent or erratic signal. The cause is most often the sensor, its connector or the wiring.

Can I drive with P03AD?

Briefly and carefully if the engine runs smoothly. If it shakes, misfires or the check engine light flashes, don't drive, to avoid damaging the catalytic converter.

How do I tell a bad sensor from bad wiring?

Wiggle the connector and harness with the engine running while watching the signal. If it drops out when you move them, the wiring or connection is at fault, not the sensor.

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.