P03B7

What it means

P03B7 is a generic powertrain code meaning the engine control module has detected an intermittent or erratic signal from the cylinder 4 pressure sensor circuit. The signal dropped out, jumped or became implausible compared with expected values or the other cylinders' sensors. This sensor type is only fitted to certain engines, so the layout depends on the model.

Symptoms

• Engine warning light on
• Rough running or misfire on cylinder 4
• Poor or uneven idle
• Reduced power or the engine running in a limp mode
• Hesitation or poor combustion control under load
• Fault appearing and disappearing

Possible causes

• Damaged, chafed or corroded wiring to the cylinder 4 pressure sensorlikely
• Loose, corroded or contaminated connector at the sensor or control modulelikely
• Faulty cylinder 4 pressure sensorpossible
• Sensor supply or reference voltage or ground fault shared with other sensorspossible
• Heat, oil or coolant contamination affecting the sensor or its harnesspossible
• Internal fault in the engine control modulerare
• Underlying mechanical problem in cylinder 4 giving erratic pressure readingsrare

How to diagnose

1. Read all stored and pending codes and note freeze frame data such as engine speed, load and temperature when the fault set.
2. Check for other cylinder pressure sensor, misfire or sensor supply codes, which may point to a shared cause.
3. Inspect the cylinder 4 sensor harness and connector for chafing, heat damage, oil contamination, bent pins and corrosion.
4. Wiggle-test the harness and connector with the engine running while watching live cylinder pressure data for dropouts.
5. Check the sensor supply voltage, signal and ground at the connector against the manufacturer's specification.
6. Check wiring continuity and resistance between the sensor and control module, and look for shorts to ground or voltage.
7. Compare cylinder 4 live data with the other cylinders to see whether the signal is implausible.
8. If the wiring tests good, check the sensor and cylinder condition following model-specific procedures before condemning the module.

How to fix

• Repair or replace damaged wiring and renew any faulty terminals.
• Clean, secure or replace the affected connector.
• Replace the cylinder 4 pressure sensor if it fails testing, following the manufacturer's procedure.
• Correct any supply or ground fault affecting the sensor circuit.
• Repair any mechanical fault in cylinder 4 that is found.
• Have the engine control module checked or replaced only after wiring and sensor faults are ruled out.

Can I keep driving?

Nearby codes

• P03B6GenericCylinder 4 Pressure Sensor Circuit High
• P03B8GenericCylinder 4 Pressure Too Low