Damaged, chafed or corroded wiring to the cylinder 3 pressure sensor (short to earth or open circuit); Poor connection or water ingress at the sensor connector; Faulty cylinder 3 pressure sensor; Loss of sensor supply or reference voltage, or a faulty earth; Wiring damage from heat or vibration near the cylinder head or harness routing; Fault inside the engine control unit or its sensor input circuit; Outdated control unit software where the manufacturer has issued a fix for this code.

P03AB

Cylinder 3 Pressure Sensor Circuit Low.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
AB: FaultThe specific fault in that area

What it means

P03AB is a generic code meaning the engine control unit has detected a low voltage signal from the cylinder 3 pressure sensor circuit. The sensor measures in-cylinder combustion pressure, and the control unit saw a signal below the expected range, which points to a short to earth, an open circuit, a lost supply or a faulty sensor. Only engines fitted with in-cylinder pressure sensors will show this code, and the exact sensor design and how it is wired depends on the model and engine.

Symptoms

Engine warning light on
Rough running or uneven idle
Hesitation or reduced power
Poor fuel economy
Rough running on start-up
Engine running in a reduced-performance mode

Possible causes

Damaged, chafed or corroded wiring to the cylinder 3 pressure sensor (short to earth or open circuit)likely
Poor connection or water ingress at the sensor connectorlikely
Faulty cylinder 3 pressure sensorlikely
Loss of sensor supply or reference voltage, or a faulty earthpossible
Wiring damage from heat or vibration near the cylinder head or harness routingpossible
Fault inside the engine control unit or its sensor input circuitrare
Outdated control unit software where the manufacturer has issued a fix for this coderare

How to diagnose

Read all stored codes and freeze frame data, noting engine load, speed and temperature when the fault set, and check for other pressure sensor codes on different cylinders.
Check for manufacturer service information or bulletins relevant to the model and engine.
Visually inspect the cylinder 3 pressure sensor, its connector and the surrounding harness for chafing, heat damage, corrosion, moisture or loose pins.
Clear the code and see if it returns immediately or only after the engine is warm or the harness is moved (wiggle test).
With the connector unplugged, check the supply, reference and earth at the harness side against the wiring diagram for the model.
Test the signal wire for continuity and for a short to earth or to other wires, with the control unit disconnected as the wiring diagram directs.
Compare the sensor's live data with the other cylinders at idle, if the engine supports this, to see if the cylinder 3 reading is implausibly low.
Check the control unit for available software updates and confirm the fault is not due to an internal control unit fault only after wiring and sensor are proven good.

How to fix

Repair or replace damaged wiring, and secure the harness away from heat and abrasion.
Clean, dry and repair or replace corroded or loose connector terminals.
Replace the cylinder 3 pressure sensor if it fails testing, following the manufacturer's torque and fitting procedure.
Restore the missing supply or earth by repairing the circuit fault found.
Update the control unit software only if the manufacturer lists an update as the fix for this fault.
Repair or replace the control unit only when all wiring and the sensor are proven good.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but engine control may be degraded and the fault could get worse. Have it diagnosed soon, and stop driving if the engine runs very roughly or loses power badly.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.