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 reading how much special fluid (called reductant or DEF) is left in the tank. It's like when your video game console can't tell how much battery is left in the controller.
The reductant level sensor B is responsible for measuring the amount of diesel exhaust fluid (DEF) in the tank. This code is triggered when the sensor's readings are outside the expected range.
The P21A9 code indicates an issue with the reductant level sensor B circuit. This sensor is part of the vehicle's emissions control system, specifically for monitoring the DEF level. The circuit range/performance issue suggests that the sensor is not providing readings within the expected parameters, which could be due to electrical faults or sensor malfunction.
• Check Engine Light is on
• Incorrect DEF level reading
• Possible reduction in engine performance
• Faulty reductant level sensor
• Wiring issues in the sensor circuit
• DEF tank contamination
Reductant: A fluid used in diesel engines to reduce emissions
DEF: Diesel Exhaust Fluid, a type of reductant
• Use an OBD-II scanner to confirm the code
• Inspect the wiring and connectors for damage
• Test the reductant level sensor for proper operation
• Replace the reductant level sensor
• Repair or replace damaged wiring
• Clean the DEF tank if contaminated
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $400
Moderate
• Ford F-250
• Chevrolet Silverado
• Ram 2500
• Regularly check and refill DEF
• Inspect wiring for damage periodically
• Use high-quality DEF
Sensor Issue
• Do not ignore the Check Engine Light
• Have the vehicle inspected by a professional
• Ensure DEF is topped up regularly
Check vehicle warranty for emissions-related coverage
This code has become more common with the introduction of stricter emissions standards requiring DEF systems.
Moderate – Addressing this issue promptly can prevent further emissions system problems.
Ignoring emissions-related issues may lead to failing emissions tests and potential fines.
• Vehicle must be in a safe location
• Engine should be off during inspection
The reductant level sensor is typically located in or near the DEF tank, which is usually at the rear of the vehicle.
Q: Can I drive with a P21A9 code?
A: It's possible to drive, but it's best to fix the issue soon to avoid emissions problems.
Q: What happens if I ignore this code?
A: Ignoring the code may lead to reduced engine performance and potential legal issues with emissions.
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