Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
The car's computer isn't getting a signal from a sensor that checks how much pollution is coming out of the exhaust on one side of the engine.
The NOx sensor is responsible for measuring nitrogen oxide levels in the exhaust gases. This code indicates that the sensor's signal is not being received by the engine control module (ECM) for Bank 2.
The NOx sensor monitors the level of nitrogen oxides in the exhaust gases. Bank 2 refers to the side of the engine that does not contain cylinder 1. When the ECM does not receive a signal from this sensor, it cannot accurately control emissions, leading to the P124F code being set.
• Check Engine Light illuminated
• Possible decrease in fuel efficiency
• Failed emissions test
• Faulty NOx sensor
• Wiring issues such as damaged wires or connectors
• Faulty ECM
NOx: Nitrogen Oxides, pollutants produced during combustion
ECM: Engine Control Module, the computer that manages engine functions
• Scan the vehicle for additional codes
• Inspect the NOx sensor and related wiring for damage
• Test the NOx sensor signal with a multimeter
• Replace the faulty NOx sensor
• Repair or replace damaged wiring or connectors
• Reprogram or replace the ECM if necessary
• OBD-II scanner
• Multimeter
• Socket set
$200 - $600
Moderate
• Volkswagen Passat
• Audi A6
• BMW 3 Series
• Regular maintenance and inspection of the exhaust system
• Ensure all sensors are clean and functioning
• Use high-quality fuel to reduce emissions
Sensor Issue
• Do not ignore the check engine light; have the vehicle inspected promptly.
• Consider regular diagnostics to catch issues early.
Check with the vehicle manufacturer; emissions-related components may have extended warranties.
The P124F code has been associated with vehicles that experience high mileage or poor maintenance practices.
Moderate – This issue affects emissions and should be addressed to ensure the vehicle meets environmental standards.
Operating a vehicle with a malfunctioning emissions system may violate environmental regulations.
• Vehicle at operating temperature
• Engine running
The NOx sensor is typically located in the exhaust system, downstream of 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 damage to the catalytic converter.
Q: Can I drive with a P124F code?
A: While the vehicle may still be drivable, it is not recommended to ignore the issue as it can lead to further damage and higher emissions.
High-End · Full-system diagnostics
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Network faults often require full-system access instead of a generic code reader alone.
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Universal · Digital multimeter
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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Universal · Wire connectors and repair kit
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.