P03B5: Cylinder 4 Pressure Sensor Circuit Low — what it means, the affected system and what to check before replacing parts.
Meaning, symptoms, causes and checks
P03B5 describes a low electrical input from the cylinder 4 pressure-sensor circuit. A low signal is not the same as confirmed low physical pressure inside that cylinder.
Affected system: Cylinder pressure and combustion monitoring
Symptoms
- Warning light may illuminate
- Related system function may be impaired
- Vehicle-specific symptoms vary
Possible causes
- Mechanical timing or operating issue, sensor or actuator fault, connector or wiring damage
- Related wiring, connector, power or ground fault
- Vehicle-specific mechanical or control issue
What to check
- Record stored and pending codes and freeze-frame data
- Record freeze-frame conditions; compare relevant live data and inspect mechanical operation, wiring and related fault codes before replacing parts.
- Confirm measured values against the vehicle service information
- Retest under the conditions that set the code
- Record freeze-frame conditions; compare relevant live data and inspect mechanical operation, wiring and related fault codes before replacing parts.
- Repair the verified cause and confirm the code does not return
Also written as: P03B5-00, P03B500, PO3B5 (some scan tools add the fault-type byte, e.g. -00).