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 saying that a sensor that checks how much special fluid is in the tank is not working right. It's like when your video game controller says the battery is low.
The P21AF code indicates that the reductant level sensor C is reporting a low voltage condition to the engine control module (ECM). This sensor is responsible for measuring the amount of diesel exhaust fluid (DEF) in the tank.
The reductant level sensor C measures the level of diesel exhaust fluid in the tank. The ECM monitors the sensor's circuit for voltage levels within a specified range. If the voltage is lower than expected, the ECM triggers the P21AF code.
• Check Engine Light illuminated
• Possible DEF warning light
• Reduced engine performance
• Faulty reductant level sensor
• Wiring issues such as shorts or open circuits
• Defective ECM
ECM: Engine Control Module
DEF: Diesel Exhaust Fluid
• Use an OBD-II scanner to confirm the code
• Inspect the wiring and connectors for damage
• Test the reductant level sensor voltage
• Replace the faulty reductant level sensor
• Repair or replace damaged wiring
• Reprogram or replace the ECM if necessary
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $500
Moderate
• Ford F-250
• Chevrolet Silverado
• Ram 2500
• Regularly check and maintain DEF levels
• Inspect wiring for wear and tear
• Ensure proper sensor installation
Sensor Issue
• Do not ignore the warning lights on your dashboard
• Schedule regular maintenance checks
• Consult a professional mechanic if unsure
Sensor-related repairs may be covered under the vehicle's emissions warranty.
This code has become more common with the increased use of DEF systems in diesel engines to meet emissions standards.
Moderate – Addressing this issue promptly can prevent further engine performance issues.
Ignoring emissions-related codes can lead to increased pollution and may be illegal in some regions.
• Engine running
• DEF tank with sufficient fluid
The reductant level sensor is typically located in or near the diesel exhaust fluid tank.
Q: Can I drive with a P21AF code?
A: It's possible to drive, but it's recommended to fix the issue soon to avoid reduced engine performance.
Q: What happens if I ignore this code?
A: Ignoring the code can lead to reduced engine power and increased emissions.
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