Engine

P03B7 — Cylinder 4 Pressure Sensor Circuit Intermittent/Erratic

Severity: medium Drive with care, to a shop

What P03B7 means

Some engines use in-cylinder pressure sensors so the control module can monitor combustion and adjust engine operation. P03B7 sets when the cylinder 4 sensor signal drops out or jumps around outside the expected range. The cause may be the sensor, its wiring or connector, or rarely the control module.

Symptoms

  • Check Engine Light on
  • Rough idle or engine shake
  • Misfire feel
  • Loss of power and sluggish acceleration
  • Worse fuel economy
  • Occasional hard starting

Possible causes

  1. Failed cylinder 4 pressure sensor
  2. Damaged wiring or intermittent connection in the sensor circuit
  3. Corroded or loose connector terminals
  4. Oil or moisture in the connector
  5. Mechanical problem or misfire in cylinder 4
  6. Control module fault (uncommon)

How to diagnose

  1. Read all codes and freeze frame data, and look for misfire or other cylinder-related codes
  2. Inspect the cylinder 4 sensor harness and connector for chafing, oil, corrosion and heat damage
  3. Wiggle the harness and connector with the engine running while watching scan tool data
  4. Check sensor power, ground and signal wires against the factory wiring diagram
  5. Test wire continuity and resistance between the sensor and the control module
  6. Check the spark plug, coil and injector on cylinder 4 to rule out a mechanical cause
  7. Run a compression test on cylinder 4 if needed
  8. If the wiring is good, test or replace the sensor before suspecting the control module

Common fixes

  • Repair the wiring or replace a damaged connector
  • Clean the terminals and secure the connector
  • Replace the cylinder 4 pressure sensor
  • Fix any mechanical fault found in cylinder 4
  • Repair, replace or reprogram the control module if confirmed faulty

Questions and answers

What does P03B7 mean?

The engine computer sees an unstable or dropping signal from the cylinder 4 pressure sensor. Wiring, the connector or the sensor itself are the most common causes.

Can I drive with P03B7?

Briefly and carefully if the engine runs smoothly. If it misfires, the check engine light flashes or power drops, stop to avoid damaging the catalytic converter.

How do I fix P03B7?

Start by inspecting the wiring and connector at the cylinder 4 sensor, then test the circuit with a multimeter. If the wiring is fine, the sensor is usually replaced.

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.