Cylinder 4 injector sticking open or leaking at the nozzle tip; Carbon or debris holding the injector seat open; Excessive fuel rail pressure caused by a faulty pressure regulator or pressure control fault; Damaged injector seals or O-rings allowing fuel to leak around the injector; Injector driver circuit or wiring fault causing the injector to be held open; Contaminated or poor quality fuel affecting injector sealing; Fault in the engine control unit injector driver.

P02A9

Cylinder 4 - Injector Leaking.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
A9: FaultThe specific fault in that area

What it means

P02A9 means the engine control unit has detected that the cylinder 4 fuel injector is leaking or dripping fuel when it should be closed. The ECU usually infers this from fuel trim, rail pressure behaviour or misfire and combustion data that point to excess fuel entering that cylinder. The exact detection method varies by engine and manufacturer.

Symptoms

Engine management light on
Rough idle or noticeable misfire, especially on cylinder 4
Hard starting or long cranking after the engine has been standing
Strong smell of fuel from the exhaust
Poor fuel economy
Possible fuel dilution of the engine oil

Possible causes

Cylinder 4 injector sticking open or leaking at the nozzle tiplikely
Carbon or debris holding the injector seat openlikely
Excessive fuel rail pressure caused by a faulty pressure regulator or pressure control faultpossible
Damaged injector seals or O-rings allowing fuel to leak around the injectorpossible
Injector driver circuit or wiring fault causing the injector to be held openpossible
Contaminated or poor quality fuel affecting injector sealingrare
Fault in the engine control unit injector driverrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine temperature, load and fuel trims when the code set
Check for related misfire codes, fuel trim codes or rail pressure codes that point to a wider fuel system fault
Inspect the cylinder 4 injector wiring and connector for damage, corrosion, water ingress or poor pin tension
Check the engine oil level and smell the oil for fuel dilution
Look for external fuel leaks around the cylinder 4 injector and fuel rail
Monitor fuel rail pressure and fuel trims with a scan tool, and check that pressure holds after shutdown, following the manufacturer's procedure
Test the cylinder 4 injector electrical resistance and operation against the manufacturer's specification, and compare its balance or leak-off with other cylinders where the engine allows
Check cylinder 4 spark plug condition for signs of excess fuel

How to fix

Replace the cylinder 4 injector if it is confirmed leaking or sticking, and fit new seals as specified for the engine
Repair or replace damaged wiring or connectors in the injector circuit
Repair the fuel pressure control fault if rail pressure is found to be too high or not holding
Replace the fuel and change the engine oil and filter if fuel dilution or contamination is confirmed
Clean or replace fouled spark plugs and recheck after the repair, then clear the code and road test to confirm it does not return

Can I keep driving?

High severity

Limit driving and have it checked promptly, as a leaking injector can wash the cylinder bores, dilute the engine oil and damage the engine or catalyst. If the engine runs roughly or smells strongly of fuel, stop driving and arrange recovery.

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