Leaking or sticking fuel injector on cylinder 1 delivering too much fuel; Injector wiring, connector or driver fault affecting cylinder 1 injector; Intake air restriction or fault specific to cylinder 1, such as a carbon-blocked port or valve, or an intake valve not seating properly; Low compression or valve problem on cylinder 1 causing the cylinder to be misread; Exhaust leak or faulty exhaust gas oxygen sensor giving a false rich reading for that cylinder; Fuel pressure too high or fuel system fault affecting all cylinders, with cylinder 1 simply the first to hit its limit; Outdated or faulty control unit software where the manufacturer has issued a fix.

P029B

Cylinder 1 - Fuel Trim at Min Limit.

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)
9B: FaultThe specific fault in that area

What it means

P029B means the engine control unit is using individual cylinder fuel trim to correct cylinder 1 and the correction has reached its minimum limit, so it cannot remove any more fuel. The unit sees cylinder 1 running richer than the others or than target, and it has run out of adjustment. How cylinder 1 is monitored (exhaust sensor readings or crankshaft speed changes) depends on the engine, so check the manufacturer data for the vehicle.

Symptoms

Engine management warning light on
Rough idle or slight shake at idle
Smell of unburnt fuel or black smoke from the exhaust
Higher than normal fuel consumption
Possible hesitation or uneven running under load
Other fuel trim or misfire codes stored alongside

Possible causes

Leaking or sticking fuel injector on cylinder 1 delivering too much fuellikely
Injector wiring, connector or driver fault affecting cylinder 1 injectorpossible
Intake air restriction or fault specific to cylinder 1, such as a carbon-blocked port or valve, or an intake valve not seating properlypossible
Low compression or valve problem on cylinder 1 causing the cylinder to be misreadpossible
Exhaust leak or faulty exhaust gas oxygen sensor giving a false rich reading for that cylinderpossible
Fuel pressure too high or fuel system fault affecting all cylinders, with cylinder 1 simply the first to hit its limitrare
Outdated or faulty control unit software where the manufacturer has issued a fixrare

How to diagnose

Read all stored and pending codes and note freeze frame data, including engine load, temperature and fuel trim values
Check for other codes such as misfire, other cylinder trim or injector circuit faults, and deal with those first
Inspect the cylinder 1 injector connector and wiring for damage, corrosion, or a poor pin fit
Compare short and long term fuel trims, and live cylinder trim values if the data is available, to see whether the fault is only on cylinder 1 or across the engine
Check fuel pressure against specification and look for fuel in the engine oil or a strong fuel smell
Inspect the exhaust for leaks near the sensors and check the oxygen sensor readings for plausibility
Test injector operation and spray or flow on cylinder 1, following the procedure for the engine concerned
Carry out a compression or leak-down test on cylinder 1 if injector and air supply checks are fine, and check for any software updates for the model

How to fix

Replace or professionally clean and flow-test the cylinder 1 injector if it is leaking or sticking
Repair or replace damaged injector wiring or connectors
Clean carbon deposits from the intake port or valves on cylinder 1 where the engine design allows, or repair the valve fault
Repair the mechanical fault found by compression or leak-down testing
Repair exhaust leaks or replace a faulty oxygen sensor confirmed by testing
Update the control unit software only if the manufacturer lists it as a fix for this fault

Can I keep driving?

Medium severity

The car can usually be driven for a short time if it runs smoothly, but book it in soon. Prolonged over-fuelling can wash oil from the cylinder wall, dilute the engine oil and damage the catalytic converter, so avoid long journeys or heavy loads, and stop if it runs very roughly or the warning light flashes.

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