Engine

P03B6 — Cylinder 4 Pressure Sensor Circuit High

Severity: medium Drive with care, to a shop

What P03B6 means

The engine control module monitors the cylinder 4 pressure sensor, which measures combustion chamber pressure and helps judge combustion quality. P03B6 sets when the signal voltage stays above the allowed range. The cause may be the sensor, a wiring fault, or, less often, the control module.

Symptoms

  • Check Engine light on
  • Rough idle and vibration
  • Reduced power and sluggish acceleration
  • Misfire or uneven combustion in cylinder 4
  • Possible limp mode

Possible causes

  1. Failed cylinder 4 pressure sensor
  2. Damaged wiring or corroded connector (open circuit, short to voltage)
  3. Poor power or ground connection in the sensor circuit
  4. ECM fault (uncommon)
  5. Mechanical problem in cylinder 4 (uncommon)

How to diagnose

  1. Scan all codes and freeze frame data and look for other cylinder or sensor codes
  2. Inspect the cylinder 4 sensor harness and connector for oil, corrosion and chafed insulation
  3. Check reference voltage and ground at the sensor with a multimeter per the wiring diagram
  4. Test the signal wire for a short to voltage or an open circuit
  5. Compare live sensor data with the other cylinders on a scan tool
  6. Test the sensor per manufacturer procedure or swap in a known good one
  7. If sensor and wiring are fine, check the ECM and cylinder 4 compression

Common fixes

  • Replace the cylinder 4 pressure sensor
  • Repair or replace damaged wiring and the connector
  • Restore the power or ground connection
  • Replace and program the ECM if confirmed faulty

Questions and answers

What does P03B6 mean?

The ECM detected a too-high voltage in the cylinder 4 pressure sensor circuit. The sensor or its wiring is the usual culprit.

Can I drive with P03B6?

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

Will clearing the code fix P03B6?

No. Clearing only erases the code, and it will return until the sensor or wiring fault is repaired.

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.