Clogged or partially blocked cylinder 5 fuel injector (deposits or debris); Contaminated or poor-quality fuel causing injector deposits or a blocked filter screen; Wiring or connector fault on the cylinder 5 injector circuit giving reduced or inconsistent injector operation; Low fuel pressure or restricted fuel supply affecting the cylinder 5 injector more than others (depends on engine layout); Air leak or carbon build-up at the cylinder 5 intake port causing a lean condition that is read as a restriction; Faulty injector internal electrical or mechanical fault (weak coil, sticking pintle); Fault in the engine control unit injector driver or outdated calibration (only where a known issue is documented for the engine).

P02AC

Cylinder 5 - 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)
AC: FaultThe specific fault in that area

What it means

P02AC means the engine control unit has detected that the fuel injector on cylinder 5 is restricted, so it is delivering less fuel than commanded. The fault is normally set when fuel trim, injector balance or cylinder contribution data shows cylinder 5 running lean or underperforming compared with the other cylinders. The exact monitoring method varies by engine and manufacturer.

Symptoms

Engine management light on
Rough idle or uneven running, especially when cold
Misfire or hesitation under load
Poor fuel economy
Loss of power
Hard starting

Possible causes

Clogged or partially blocked cylinder 5 fuel injector (deposits or debris)likely
Contaminated or poor-quality fuel causing injector deposits or a blocked filter screenpossible
Wiring or connector fault on the cylinder 5 injector circuit giving reduced or inconsistent injector operationpossible
Low fuel pressure or restricted fuel supply affecting the cylinder 5 injector more than others (depends on engine layout)possible
Air leak or carbon build-up at the cylinder 5 intake port causing a lean condition that is read as a restrictionrare
Faulty injector internal electrical or mechanical fault (weak coil, sticking pintle)possible
Fault in the engine control unit injector driver or outdated calibration (only where a known issue is documented for the engine)rare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including fuel trims, load, engine temperature and rpm when the fault set
Check for other lean, misfire or fuel pressure codes that point to a wider fuel or air problem
Inspect the cylinder 5 injector connector and wiring for damage, corrosion, loose pins or heat damage
Look at live data for short and long term fuel trims and any injector balance or cylinder contribution values, comparing cylinder 5 with the others
Check for intake air leaks and vacuum leaks near cylinder 5, such as the manifold gasket, hoses and seals
Test fuel pressure and volume against the manufacturer's specification for that engine
Test the injector electrical resistance and driver signal, and compare the spray pattern and flow rate with a known good injector
Swap the cylinder 5 injector with another cylinder (where the engine allows) and see whether the fault follows the injector

How to fix

Clean or replace the restricted cylinder 5 injector, following the manufacturer's procedure for the engine
Repair or replace damaged wiring, terminals or connectors on the injector circuit
Replace the fuel filter and correct any fuel supply or pressure fault found, and drain and refill with good quality fuel if contamination is confirmed
Repair any intake air or vacuum leak affecting cylinder 5
Replace the engine control unit or apply a manufacturer-approved calibration update only where a driver fault or outdated calibration is confirmed as the cause

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but book it in soon. A restricted injector can cause a lean cylinder, misfires and higher combustion temperatures, which may damage the catalytic converter or engine if left. If the engine is misfiring badly or the warning light flashes, stop driving and get it checked.

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