Fuel injector on cylinder 4 partly blocked by deposits or contamination; Injector internal wear or sticking, giving poor spray pattern or reduced flow; Low fuel pressure or restricted fuel delivery, such as a clogged filter or weak pump, affecting the injector; Wiring, connector or terminal fault on the cylinder 4 injector circuit causing weak or inconsistent injector operation; Poor quality or contaminated fuel causing deposits or debris in the injector; Carbon build-up on the intake valves or in the cylinder 4 port causing a fuelling or mixture problem that mimics a restriction (depends on the engine type); Fault in the ECU injector driver.

P02A8

Cylinder 4 - Injector Restricted.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
A8: FaultThe specific fault in that area

What it means

P02A8 means the engine control unit has detected that the fuel injector on cylinder 4 is restricted, so it is not delivering the expected amount of fuel. The ECU usually sets this after seeing that the cylinder 4 fuelling correction, injector flow estimate or cylinder balance is outside its limits compared with the other cylinders. How the restriction is detected varies by engine and fuel system, so the exact test depends on the model.

Symptoms

Engine misfire or rough running, mainly at idle or low load
Hesitation or reduced power under acceleration
Malfunction indicator lamp on
Poor fuel economy
Hard starting or uneven idle
Possible fuel smell or black smoke if the mixture is unbalanced

Possible causes

Fuel injector on cylinder 4 partly blocked by deposits or contaminationlikely
Injector internal wear or sticking, giving poor spray pattern or reduced flowlikely
Low fuel pressure or restricted fuel delivery, such as a clogged filter or weak pump, affecting the injectorpossible
Wiring, connector or terminal fault on the cylinder 4 injector circuit causing weak or inconsistent injector operationpossible
Poor quality or contaminated fuel causing deposits or debris in the injectorpossible
Carbon build-up on the intake valves or in the cylinder 4 port causing a fuelling or mixture problem that mimics a restriction (depends on the engine type)rare
Fault in the ECU injector driverrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting load, engine temperature and fuel trims when the fault set
Check for related codes such as misfires, fuel trim, fuel pressure or injector circuit faults, and diagnose those first if present
Inspect the cylinder 4 injector connector, terminals and wiring for damage, corrosion, or poor contact
Review live data for fuel trims and misfire counters per cylinder to confirm that cylinder 4 is the one affected
Check fuel pressure and delivery against the manufacturer's specification, including the fuel filter condition where one is fitted
Test the injector electrical resistance and driver signal, and swap it with another cylinder's injector to see whether the fault follows it
Carry out an injector flow and leak test or a spray pattern check as the manufacturer procedure allows
Check the spark plug and compression on cylinder 4 to rule out a mechanical cause of the poor combustion

How to fix

Clean the injector if the manufacturer permits it, or replace it if it is blocked, worn or out of specification
Repair or replace damaged wiring, terminals or the connector on the injector circuit
Replace the fuel filter and repair any fuel delivery fault such as a weak pump or pressure regulation problem
Drain and replace contaminated fuel, then refill with good quality fuel
Clean carbon deposits from the intake side if inspection shows they are a contributing factor, following the engine maker's procedure
Update the ECU software only if the manufacturer lists an outdated calibration as a known cause for this fault

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but book a repair soon because a restricted injector can cause a lean cylinder, misfires and possible damage to the catalytic converter or engine. If the engine misfires badly or the warning lamp flashes, stop driving and have it checked.

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