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 can't get a signal from a special sensor that checks for pollution in the exhaust.
The NOx sensor is supposed to send signals to the car's computer about the levels of nitrogen oxides in the exhaust. This code means the signal is missing.
The P124D code indicates that the Engine Control Module (ECM) is not receiving a valid signal from the NOx sensor located on Bank 1. This sensor is crucial for monitoring and controlling emissions, and its absence can affect engine performance and emissions compliance.
• Check Engine Light illuminated
• Increased emissions
• Possible reduction in engine performance
• Faulty NOx sensor
• Wiring issues such as damaged wires or poor connections
• Faulty ECM or software issues
NOx Sensor: A sensor that measures nitrogen oxides in the exhaust.
ECM: Engine Control Module, the computer that manages engine functions.
• Use an OBD-II scanner to confirm the P124D code.
• Inspect the wiring and connections to the NOx sensor.
• Test the NOx sensor for proper operation.
• Replace the faulty NOx sensor.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$200 - $600
Moderate
• BMW 3 Series
• Ford F-150
• Volkswagen Jetta
• Regularly inspect and maintain the exhaust system.
• Ensure timely servicing of sensors.
• Avoid using poor quality fuel.
Sensor Issue
• Have your vehicle diagnosed by a professional mechanic.
• Do not ignore the Check Engine Light.
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code has become more common as vehicles incorporate more sensors to meet stringent emissions standards.
Moderate – It should be addressed soon to avoid increased emissions and potential engine performance issues.
Ignoring emissions-related issues may lead to failing emissions tests and potential fines.
• Engine running
• Vehicle at operating temperature
The NOx sensor is typically located in the exhaust system, often near the catalytic converter on Bank 1.
Q: Can I drive with a P124D code?
A: It's possible to drive, but it's not recommended as it can lead to increased emissions and potential engine issues.
Q: How do I reset the P124D code?
A: After repairs, use an OBD-II scanner to clear the code. If the issue is resolved, it should not return.
Pro · Four-system diagnostics
A handheld scanner aimed at engine, transmission, ABS, and airbag diagnostic work.
Chassis and ABS faults usually need a scanner that can read brake-system data directly.
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Universal · Torque wrench
Useful when reassembly torque matters for wheel, suspension, and under-hood fasteners.
Useful when wheel, hub, or suspension hardware needs correct reassembly torque.
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Universal · Drive-on ramps
Helpful for safer access underneath the vehicle during exhaust, EVAP, and underbody inspection work.
Helpful for safer access during underbody inspection work.
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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.