Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the computer in your car has noticed that the mixture of air and fuel going into cylinder 8 isn't right, and it can't adjust it anymore.
The engine control module (ECM) has detected that the air-fuel ratio for cylinder 8 is not within the expected range and the system has reached its limit trying to adjust it.
The P231B code indicates that the ECM has identified an air-fuel ratio imbalance in cylinder 8. This imbalance means that the mixture of air and fuel entering the cylinder is not optimal, which can affect engine performance and emissions. The ECM has attempted to correct this imbalance but has reached its adjustment limits.
• Check engine light on
• Poor engine performance
• Rough idle
• Increased fuel consumption
• Faulty fuel injector for cylinder 8
• Vacuum leak affecting cylinder 8
• Faulty oxygen sensor
• Exhaust leak near cylinder 8
• Faulty mass air flow sensor
ECM: Engine Control Module
OBD-II: On-Board Diagnostics II
Air-Fuel Ratio: The ratio of air to fuel in the combustion mixture
• Use an OBD-II scanner to confirm the code
• Inspect the fuel injector for cylinder 8
• Check for vacuum leaks around cylinder 8
• Test the oxygen sensor functionality
• Inspect for exhaust leaks near cylinder 8
• Replace or clean the fuel injector for cylinder 8
• Repair any vacuum leaks
• Replace faulty oxygen sensor
• Fix any exhaust leaks
• Replace the mass air flow sensor if necessary
• OBD-II scanner
• Multimeter
• Fuel injector cleaner
• Vacuum leak detector
$150 - $500
Moderate
• Ford F-150
• Chevrolet Silverado
• Toyota Camry
• Regular maintenance and tune-ups
• Use quality fuel
• Inspect and replace air filters regularly
Engine Performance
• Get the issue diagnosed and repaired promptly to avoid further damage
• Monitor fuel consumption for any unusual changes
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code has been associated with vehicles that have high mileage or have not been maintained regularly.
Moderate – While the car can still be driven, it's important to address the issue to prevent further engine problems.
Ignoring this code can lead to increased emissions, which may not comply with local environmental regulations.
• Engine at operating temperature
• Vehicle in closed-loop fuel control
Cylinder 8 is typically located at the rear of the engine on the passenger side in V8 engines.
Q: Can I drive with a P231B code?
A: While you can drive with this code, it's best to get it fixed soon to avoid further engine issues.
Q: Will a P231B code affect my vehicle's emissions?
A: Yes, an air-fuel ratio imbalance can increase emissions and may cause your vehicle to fail an emissions test.
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Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
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Fitment Required · Vehicle-fitment part
Relevant when the code or supporting diagnostics point toward upstream or downstream oxygen-sensor faults.
This code family often involves upstream or downstream oxygen-sensor diagnosis.
Verify exact sensor position and vehicle fitment before buying.
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Fitment Required · Vehicle-fitment part
Relevant for airflow, fuel-trim, and intake-metering faults after confirming the sensor is actually at fault.
Airflow and fuel-trim codes can involve the mass air flow sensor after proper diagnosis.
Verify the sensor design and fitment for your exact vehicle.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.