What Does P02AC Mean?
The ECM has detected that the fuel injector on cylinder 5 is restricted, meaning it cannot deliver the commanded amount of fuel due to a partial blockage or reduced flow capacity. The ECM identifies this through individual cylinder fuel trim corrections that show the injector is consistently underperforming. The driver may notice a misfire on cylinder 5, hesitation during acceleration, rough idle, and reduced engine power.
Common Causes
40%
Clogged injector filter basket or nozzle tip from fuel contaminants, varnish, or carbon deposits restricting fuel flow
25%
Internal injector deposits from low-quality fuel or ethanol buildup causing partial blockage of the spray orifices
15%
Kinked or pinched fuel supply line reducing fuel flow to the rail and affecting the weakest injector first
12%
Clogged in-line fuel filter or fuel pump strainer reducing overall system fuel pressure and flow
8%
Corroded or damaged injector electrical connector causing intermittent operation that mimics restriction
Diagnostic Steps
1
Check live data for cylinder 5 individual fuel trim — a high positive trim value indicates the ECM is attempting to compensate for reduced fuel delivery from the restricted injector.
2
Perform an injector balance test by disabling each injector individually and monitoring rpm drop — cylinder 5 should cause a similar rpm drop as the others. A smaller drop indicates reduced fuel flow.
3
Remove the fuel injectors and send them for professional flow testing and ultrasonic cleaning to measure the actual flow rate compared to specification and other injectors — variation should be less than 5%.
4
Inspect the fuel rail for debris or contamination by disconnecting it and examining the injector seats and fuel passages for visible deposits or corrosion.
5
Check fuel system pressure at idle (typically 55-62 PSI for port injection) and verify it does not drop excessively under load, which would indicate a supply-side restriction.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The ECM has detected that the fuel injector on cylinder 5 is restricted, meaning it cannot deliver the commanded amount of fuel due to a partial blockage or reduced flow capacity. The ECM identifies this through individual cylinder fuel trim corrections that show the injector is consistently underpe...
The most common cause of P02AC (Cylinder 5 - Injector Restricted) is: Clogged injector filter basket or nozzle tip from fuel contaminants, varnish, or carbon deposits restricting fuel flow
Typical repair costs for P02AC range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle is generally safe to drive short distances, but the lean condition on cylinder 5 can cause elevated combustion temperatures that may damage the catalytic converter over time. Extended driving with a restricted injector can lead to engine misfires and potential piston damage from lean detonation.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P02AC to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Fuel System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
