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 is having trouble getting a good reading from the sensor that checks how much special fluid (called reductant) is left in the tank. It's like when your video game controller keeps losing connection.
The P21B1 code is triggered when the engine control module (ECM) detects an intermittent or erratic signal from the reductant level sensor C circuit.
The reductant level sensor monitors the amount of diesel exhaust fluid (DEF) in the tank. This fluid is used in the Selective Catalytic Reduction (SCR) system to reduce emissions. An intermittent or erratic circuit signal indicates that the sensor's readings are unstable, which can affect the SCR system's performance.
• Check engine light illuminated
• Possible reduction in engine power
• Increased emissions
• Faulty reductant level sensor
• Wiring issues such as damaged or corroded connectors
• Malfunctioning ECM
Reductant: A substance used to reduce emissions in a vehicle's exhaust system.
SCR: Selective Catalytic Reduction, a system that reduces emissions in diesel engines.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for damage or corrosion.
• Test the reductant level sensor for proper operation.
• Repair or replace damaged wiring or connectors.
• Replace the reductant level sensor if faulty.
• Reprogram or replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Wrench set
$150 - $500
Moderate
• Ford F-250
• Chevrolet Silverado
• Ram 2500
• Regularly inspect and maintain wiring and connectors.
• Use high-quality diesel exhaust fluid.
• Perform routine vehicle maintenance.
Sensor Issue
• Avoid driving long distances until the issue is fixed.
• Check for any recalls related to the reductant system.
• Consult a professional mechanic for accurate diagnosis.
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code has become more common with the increased use of diesel exhaust fluid systems in modern diesel engines.
Moderate – While the vehicle may still be drivable, emissions and performance can be affected.
Driving with a malfunctioning emission system may violate emissions regulations and can lead to fines.
• Vehicle must be running.
• Ensure the DEF tank is not empty.
The reductant level sensor is typically located in or near the diesel exhaust fluid tank.
Q: Can I drive with a P21B1 code?
A: It's possible to drive, but it's not recommended as it can affect emissions and engine performance.
Q: What is diesel exhaust fluid?
A: Diesel exhaust fluid (DEF) is a liquid used to reduce emissions in diesel engines.
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