Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
Your car's computer thinks there's too much fuel being used when the car is just sitting still, like when it's stopped at a traffic light.
The engine control module (ECM) detects that the air-fuel mixture is too rich (too much fuel) in Bank 2 when the vehicle is idling.
The P21FB code is triggered when the ECM identifies that the fuel mixture in Bank 2 is excessively rich during idle conditions. This can be due to various factors such as a malfunctioning fuel injector, a faulty oxygen sensor, or a problem with the fuel pressure regulator.
• Check Engine Light is on
• Poor fuel economy
• Rough idle
• Faulty oxygen sensor
• Leaking fuel injector
• Fuel pressure regulator malfunction
ECM: Engine Control Module, the computer that controls engine operation
Oxygen Sensor: A sensor that measures the amount of oxygen in the exhaust gases
• Check for any other related trouble codes
• Inspect the oxygen sensors for proper operation
• Test the fuel injectors for leaks
• Replace faulty oxygen sensor
• Repair or replace leaking fuel injectors
• Replace or repair the fuel pressure regulator
• OBD-II scanner
• Multimeter
• Fuel pressure gauge
$150 - $500
Moderate
• Ford F-150
• Chevrolet Silverado
• Toyota Camry
• Regular maintenance of fuel system
• Timely replacement of oxygen sensors
• Use quality fuel
Engine Performance
• Avoid driving with this code active for long periods
• Get the vehicle inspected by a professional mechanic
• 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 fuel system issues in various models, often related to sensor failures.
Moderate – Addressing this issue promptly can prevent further engine damage.
Driving with a rich fuel mixture can lead to increased emissions, which may not comply with local environmental regulations.
• Vehicle at idle
• Engine at operating temperature
Bank 2 refers to the side of the engine opposite the number one cylinder, typically on V-type engines.
Q: Can I drive with a P21FB code?
A: While the car may still run, it's not recommended to drive for long periods with this code active, as it can lead to further engine issues.
Q: What happens if I ignore a P21FB code?
A: Ignoring this code can result in poor fuel economy, increased emissions, and potential damage to the catalytic converter.
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A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
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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.
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.