What Does P02A9 Mean?
The ECM has detected that the fuel injector on cylinder 4 is leaking fuel, allowing unmetered fuel to enter the combustion chamber or intake manifold when the injector should be closed. This results in an overly rich condition on that cylinder, which can cause misfires, rough idle, and elevated hydrocarbon emissions. The driver may notice a strong fuel smell, black exhaust smoke, and a noticeable rough running condition especially at idle.
Common Causes
35%
Worn or damaged injector pintle seal or O-ring allowing fuel seepage past the injector tip when closed
25%
Cracked or scored injector nozzle seat preventing full shutoff of fuel flow
20%
Contaminated or corroded injector internals causing the needle valve to stick partially open
12%
Excessive fuel system pressure forcing fuel past the injector seal during closed periods
8%
Faulty injector driver circuit holding the injector partially energized
Diagnostic Steps
1
Monitor cylinder 4 short-term and long-term fuel trim values via live data — a significantly negative fuel trim (below -10%) on that cylinder confirms the ECM is compensating for a rich condition caused by the leak.
2
Perform a fuel injector balance test or cylinder power contribution test using bidirectional controls to compare cylinder 4's contribution against the other cylinders.
3
Check fuel system pressure with a gauge: key-on engine-off should hold at the specified rail pressure (typically 55-62 PSI for port injection). Monitor for excessive pressure bleed-down after shutoff, which indicates a leaking injector or check valve.
4
Remove the fuel rail with injectors attached (engine off, pressure relieved) and apply regulated fuel pressure while observing each injector tip for dripping — cylinder 4's injector should hold with no more than 1 drop per minute.
5
Inspect the cylinder 4 spark plug for heavy black carbon fouling or wet fuel deposits, which would confirm fuel is entering the cylinder when it should not be.
Estimated Repair Cost
$150 - $450
Parts + labor, varies by vehicle and location
The ECM has detected that the fuel injector on cylinder 4 is leaking fuel, allowing unmetered fuel to enter the combustion chamber or intake manifold when the injector should be closed. This results in an overly rich condition on that cylinder, which can cause misfires, rough idle, and elevated hydr...
The most common cause of P02A9 (Cylinder 4 - Injector Leaking) is: Worn or damaged injector pintle seal or O-ring allowing fuel seepage past the injector tip when closed
Typical repair costs for P02A9 range from $150 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle can be driven short distances but should be repaired soon. A leaking injector can wash the cylinder walls of oil, leading to accelerated cylinder wear, and the excess fuel can overheat and damage the catalytic converter. In severe cases, raw fuel in the exhaust creates a fire risk.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P02A9 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.
