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 car's computer found a problem with the sensors that measure pollution in the exhaust. It's like when a thermometer gives a weird reading, and you need to check if it's working right.
The P221B code indicates that the readings from two NOx sensors on Bank 2 of the engine do not match as expected.
The NOx sensors are responsible for measuring the levels of nitrogen oxides in the exhaust gases. Bank 2 refers to the side of the engine that does not contain cylinder 1 in a V-type engine. The code is set when the Engine Control Module (ECM) detects a discrepancy between the readings of NOx Sensor 1 and NOx Sensor 2 on Bank 2.
• Check Engine Light is on
• Poor fuel economy
• Failed emissions test
• Faulty NOx sensor
• Wiring or connection issues
• Exhaust leaks
NOx: Nitrogen Oxides, which are pollutants produced during combustion.
ECM: Engine Control Module, the computer that controls engine functions.
• Use an OBD-II scanner to confirm the code
• Inspect the wiring and connections to the NOx sensors
• Check for exhaust leaks around the sensors
• Replace faulty NOx sensor
• Repair or replace damaged wiring
• Fix any exhaust leaks
• OBD-II scanner
• Multimeter
• Wrench set
$200 - $600
Moderate
• Volkswagen Passat
• Audi A6
• BMW 3 Series
• Regular maintenance checks
• Timely replacement of faulty sensors
• Ensure proper exhaust system maintenance
Sensor Issue
• Have the vehicle inspected by a professional
• Do not ignore the Check Engine Light
• Consider emissions system maintenance
Check with the vehicle manufacturer for emissions-related warranty coverage.
This code has become more common with stricter emissions regulations and the increased use of NOx sensors in modern vehicles.
Moderate – It should be addressed to avoid potential emissions issues and engine performance problems.
Driving with a faulty NOx sensor may result in higher emissions, potentially violating environmental regulations.
• Engine at operating temperature
• Vehicle driven under normal conditions
The NOx sensors are located in the exhaust system, typically before and after the catalytic converter on Bank 2.
Q: What happens if I ignore this code?
A: Ignoring this code can lead to increased emissions and potential engine performance issues.
Q: Can I drive with a P221B code?
A: It's possible to drive, but it's not recommended due to potential emissions problems and reduced fuel efficiency.
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Universal · Digital multimeter
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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 catalyst-efficiency or emissions faults persist after proper diagnosis.
Catalyst-efficiency faults sometimes point toward converter problems after proper testing.
Catalytic converters are highly vehicle-specific and should not be purchased by code alone.
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.