Engine

P03C1 — Cylinder 5 Pressure Sensor Circuit Intermittent/Erratic

Severity: medium Drive with care, to a shop

What P03C1 means

The engine control module monitors the cylinder 5 pressure sensor to help judge combustion and fine-tune engine control. P03C1 sets when the signal in that circuit drops out, jumps around or goes implausible from time to time. These sensors are used only on certain engines, so the exact setup depends on the vehicle.

Symptoms

  • Check engine light on
  • Rough or uneven idle
  • Reduced power and acceleration
  • Worse fuel economy
  • Hesitation or stumbling under load
  • Possible limp mode

Possible causes

  1. Corroded, loose or damaged sensor connector
  2. Broken, chafed or shorted wiring to the sensor
  3. Failed cylinder 5 pressure sensor
  4. Poor ground or sensor supply voltage problem
  5. ECM software fault or internal failure (rare)
  6. Actual mechanical problem in the cylinder affecting pressure (rare)

How to diagnose

  1. Scan all codes and freeze frame data, noting any other cylinder or sensor faults
  2. Inspect the cylinder 5 sensor connector and harness for rubbing, oil, moisture and corrosion
  3. Wiggle the harness and connector with the engine running while watching sensor data on a scan tool
  4. Check sensor power, ground and reference voltage against the factory wiring diagram
  5. Test the signal wire for opens and shorts with a multimeter
  6. Compare the signal with the other cylinder sensors if available
  7. Check for ECM software updates or service bulletins
  8. If the electrical side is fine, check cylinder compression and condition

Common fixes

  • Clean or replace the corroded connector and terminals
  • Repair the damaged wiring harness
  • Replace the cylinder 5 pressure sensor
  • Update or reflash the ECM software
  • Replace the ECM (very rare, only after everything else is ruled out)

Questions and answers

What does P03C1 mean?

The engine computer sees an intermittent or erratic signal from the cylinder 5 pressure sensor. Wiring or connector trouble is the most common cause, the sensor itself less so.

Can I drive with code P03C1?

Briefly and carefully, yes, but don't put off diagnosis. Stop if the engine misfires badly, shakes or the check engine light flashes.

How do I fix P03C1?

Start by inspecting the cylinder 5 sensor connector and wiring. If those are good, the sensor is replaced, and in rare cases the ECM software is updated.

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.