P03B6: Cylinder 4 Pressure Sensor Circuit High

What it means

Cylinder 4 pressure sensor above upper plausibility — open signal or short to B+. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The cylinder 4 pressure sensor measures combustion pressure so the engine control module can assess how that cylinder is burning. This code sets when the cylinder 4 sensor signal is higher than the module considers plausible, which can happen if the signal circuit is open or shorted to battery voltage.

Common causes

Most likely first.

1. Open signal line
2. Connector pins corroded - high contact resistance
3. Supply wire pinched against B+ source

Symptoms

• Check-engine light

How to diagnose it

1. Check freeze-frame data and cylinder pressure readings to confirm the fault is associated with cylinder 4 and note when it occurs.
2. With the ignition off, inspect the cylinder 4 sensor connector for moisture, corrosion, damaged seals, loose fit, or pins pushed back.
3. Trace the cylinder 4 sensor wiring for chafing, pinching, or contact with a battery-positive supply, especially near the engine and harness supports.
4. While monitoring the cylinder 4 pressure signal with a scan tool, gently move the harness and connector to see whether the reading changes or the fault returns.
5. If the visual and movement checks do not locate the fault, test the signal wire for continuity and shorts to power using the vehicle wiring diagram and manufacturer's procedures.
6. If wiring and connections pass, compare the sensor output and its supply and ground circuits with the manufacturer's specification before condemning the sensor or module.

Common fixes

• Reconnect and secure a loose cylinder 4 pressure sensor connector.
• Clean or repair corroded connector terminals and replace damaged seals as needed.
• Repair an open, pinched, or chafed cylinder 4 signal wire and secure the harness away from heat and moving parts.
• Replace the cylinder 4 pressure sensor if its output remains implausibly high with the circuit verified.
• Repair a confirmed sensor supply, ground, or control-module fault.

Can I keep driving?

A check-engine light may be the only symptom, but the module may have less reliable combustion data for cylinder 4. Avoid heavy loads if the engine runs poorly, and address the fault soon because emissions and engine control can be affected.