What Does P029B Mean?
The ECM has detected that the individual cylinder fuel trim for cylinder 1 has reached its minimum (maximum lean correction) limit. The ECM is subtracting as much fuel as possible from cylinder 1, and the air/fuel ratio is still too rich. This indicates an over-fueling condition specific to cylinder 1 that the adaptive system cannot fully correct. The driver may notice rough idle, black smoke, fuel odor, or fouled spark plug on that cylinder.
Common Causes
35%
Leaking cylinder 1 fuel injector allowing fuel to drip into the cylinder when closed, over-fueling that cylinder
20%
Incorrect fuel injector installed on cylinder 1 with a higher-than-specified flow rate
20%
Carbon buildup on cylinder 1 intake valve causing fuel puddling and inconsistent fuel delivery (port injection)
15%
Cylinder 1 spark plug or ignition coil issue causing incomplete combustion and rich exhaust
10%
Low compression on cylinder 1 causing inefficient combustion and rich exhaust gas
Diagnostic Steps
1
Monitor cylinder 1 individual fuel trim percentage; confirm it is at or near the negative (lean correction) limit, typically -25% to -30%.
2
Perform a fuel injector leak-down test: with the engine off and fuel system pressurized, inspect cylinder 1 injector for dripping by removing the spark plug and looking for wetness or using a borescope.
3
Remove and inspect the cylinder 1 spark plug; a black, sooty deposit indicates rich running on that cylinder. Compare plug condition to other cylinders.
4
Test cylinder 1 injector flow rate using a flow bench or on-car injector balance test; compare flow volume to the other injectors. Flow should be within 5% of the average.
5
Check cylinder 1 compression; a weak cylinder will not combust fuel efficiently, causing rich exhaust. Compare to other cylinders (should be within 10%).
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The ECM has detected that the individual cylinder fuel trim for cylinder 1 has reached its minimum (maximum lean correction) limit. The ECM is subtracting as much fuel as possible from cylinder 1, and the air/fuel ratio is still too rich. This indicates an over-fueling condition specific to cylinder...
The most common cause of P029B (Cylinder 1 - Fuel Trim at Min Limit) is: Leaking cylinder 1 fuel injector allowing fuel to drip into the cylinder when closed, over-fueling that cylinder
Typical repair costs for P029B range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Driving is possible for short distances. An over-rich cylinder 1 will foul the spark plug, wash lubricating oil from the cylinder wall causing accelerated wear, and contaminate the catalytic converter. Extended driving in this condition risks catalytic converter failure.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P029B to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel System
Difficulty
Type
Generic (SAE)
Recommended Tools
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