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 is having trouble talking to a sensor that checks the pollution coming out of the engine.
This code indicates a performance issue with the NOx sensor processor for Bank 1, Sensor 3. The sensor is not communicating or processing data as expected.
The P23AB code is triggered when the Engine Control Module (ECM) detects a malfunction in the NOx sensor processor's performance. This sensor is responsible for measuring the levels of nitrogen oxides (NOx) in the exhaust gases. Bank 1 refers to the side of the engine with cylinder 1, and Sensor 3 is the specific sensor in question.
• Check Engine Light is on
• Reduced engine performance
• Increased emissions
• Faulty NOx sensor
• Wiring issues or poor connections
• ECM software issues
NOx: Nitrogen Oxides, 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 sensor.
• Test the NOx sensor for proper operation.
• Replace the faulty NOx sensor.
• Repair or replace damaged wiring or connectors.
• Update the ECM software if necessary.
• OBD-II scanner
• Multimeter
• Socket set
$200 - $600
Moderate
• Volkswagen Jetta
• Audi A4
• BMW 3 Series
• Regularly maintain the vehicle's exhaust system.
• Ensure all sensors are functioning properly.
• Keep the ECM software updated.
Sensor Issue
• Do not ignore the Check Engine Light.
• Have the vehicle inspected by a professional.
• Avoid driving the vehicle excessively until repaired.
Check with the vehicle manufacturer for emissions-related warranty coverage.
NOx sensor issues have been common in vehicles with advanced emissions systems, especially in diesel engines.
Moderate – Should be addressed to prevent increased emissions and potential damage to the vehicle.
Driving with a malfunctioning emissions system can lead to legal penalties and increased pollution.
• Engine at operating temperature
• Vehicle in closed-loop operation
The NOx sensor is typically located in the exhaust system, near the catalytic converter.
Q: What does a NOx sensor do?
A: A NOx sensor measures the amount of nitrogen oxides in the exhaust gases to help control emissions.
Q: Can I drive with a P23AB code?
A: It's not recommended, as it may lead to increased emissions and potential engine performance issues.
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Universal · Digital multimeter
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Useful when diagnosis points toward damaged wiring, corroded terminals, or connector 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.