Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means your car's engine is not getting enough fuel when it's just sitting still and running. It's like when you feel really hungry and can't do much because you haven't eaten enough.
The engine control module (ECM) has detected that the air-fuel mixture is too lean on Bank 1 while the engine is idling.
P21F8 indicates that the ECM has identified a lean condition in the fuel control system for Bank 1 at idle. This means there is too much air and not enough fuel in the combustion chamber, which can affect engine performance and emissions.
• Rough idle
• Check Engine Light illuminated
• Poor fuel economy
• Vacuum leak
• Faulty fuel injector
• Malfunctioning mass air flow sensor
ECM: Engine Control Module
Mass Air Flow Sensor: A sensor that measures the amount of air entering the engine
• Check for vacuum leaks in the intake system.
• Inspect and test the fuel injectors for proper operation.
• Test the mass air flow sensor for proper readings.
• Repair any vacuum leaks found.
• Replace or clean faulty fuel injectors.
• Replace the mass air flow sensor if it is malfunctioning.
• OBD-II scanner
• Vacuum gauge
• Fuel injector tester
$150 - $500
Moderate
• Toyota Camry
• Honda Accord
• Ford F-150
• Regularly inspect and replace air filters.
• Perform routine fuel system maintenance.
• Check for vacuum leaks periodically.
Engine Performance
• Do not ignore the Check Engine Light.
• Have the issue diagnosed and repaired promptly to avoid further damage.
• Consider using a fuel system cleaner periodically.
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code has been reported in vehicles with high mileage or those that have not been maintained regularly.
Moderate – It should be addressed soon to prevent potential engine damage.
Ignoring this code can lead to increased emissions, which may not comply with local environmental regulations.
• Engine must be idling.
• Vehicle should be at operating temperature.
Bank 1 refers to the side of the engine with cylinder 1. The components involved are typically located around the intake manifold and fuel rail.
Q: Can I drive my car with a P21F8 code?
A: It's not recommended to drive for extended periods with this code. It can lead to poor performance and increased emissions.
Q: What happens if I ignore the P21F8 code?
A: Ignoring it can lead to engine damage over time and may result in failing an emissions test.
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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.