P02A6 - Cylinder 4 – Fuel Trim at Maximum Limit
Last updated:
System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P02A6 is an OBD-II diagnostic trouble code indicating that the Engine Control Module (ECM) has detected a lean fuel trim condition at its maximum limit for cylinder number 4. The ECM monitors individual cylinder contribution via the crankshaft position sensor (delta speed) and oxygen sensors. When the ECM has to increase the injector pulse width beyond a specific threshold to maintain stoichiometric balance in cylinder 4, this code is triggered, signifying that the cylinder is under-performing due to lack of fuel or unmetered air intake.
Possible Causes
Clogged or faulty fuel injector (Cylinder 4)
Intake manifold air leak (vacuum leak) specifically at cylinder 4 runner
Faulty spark plug or ignition coil (causing incomplete combustion interpreted as lean)
Engine mechanical issue, such as a leaking intake valve or low compression on cylinder 4
Symptoms
Recommended Solution
- VISUAL INSPECTION: Inspect the intake manifold and vacuum lines near cylinder 4 for leaks. Check wiring harnesses for injectors and ignition coils for damage or corrosion.
- FUEL SYSTEM TESTING: Verify fuel rail pressure (typically 45-60 psi for port injection). Perform a fuel injector balance test using a scan tool to verify manual contribution.
- ELECTRICAL MEASUREMENT: Measure the resistance of the injector (should be 11-16 Ohms for most high-impedance injectors). Use an oscilloscope to verify the injector pulse signal from the ECM.
- COMPONENT SWAP: Swap fuel injector 4 with injector 1. If the code changes to P02A0, replace the injector. If the code remains P02A6, perform a compression and leak-down test.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
Do you also have
other fault codes?
See how P02A6 connects with your other fault codes. Our advanced analysis tool identifies causal relationships and root causes directly.