P029B - Cylinder 1 Fuel Trim at Max Limit
Last updated:
System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P029B is triggered when the Engine Control Module (ECM) has reached its maximum enrichment limit (Long Term Fuel Trim) while trying to compensate for an extremely lean condition specifically on cylinder 1. The ECM attempts to add more fuel by increasing the injector pulse width, but the feedback from the O2/NOx sensors indicates that the cylinder is still running lean. This typically suggests a restricted injector or a cylinder-specific mechanical issue rather than a bank-wide problem.
Possible Causes
Clogged or faulty fuel injector on cylinder 1
Intake manifold air leak near cylinder 1 (e.g., injector O-ring)
Faulty spark plug or ignition coil (misfire causing false lean reading)
Engine mechanical issue (low compression on cylinder 1) or faulty ECM driver circuit
Symptoms
Recommended Solution
Workflow
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 P029B connects with your other fault codes. Our advanced analysis tool identifies causal relationships and root causes directly.