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 the amount of a special fluid, like a cleaning liquid, in the tank. It's like when you can't tell how much juice is left in a cup because the markings are unclear.
The P21AE code indicates an issue with the sensor that measures the level of reductant fluid in the tank. This sensor is not providing readings within the expected range.
The reductant level sensor C is responsible for monitoring the amount of reductant fluid, often diesel exhaust fluid (DEF), in the vehicle's tank. This fluid is used in the selective catalytic reduction (SCR) system to reduce emissions. A range/performance issue means the sensor is not providing accurate readings, which could be due to electrical issues or sensor malfunction.
• Check engine light illuminated
• Poor engine performance
• Increased emissions
• Faulty reductant level sensor
• Wiring issues or poor connections
• Defective control module
Reductant: A substance used to reduce emissions in diesel engines.
SCR: Selective Catalytic Reduction, a system to reduce emissions.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connections to the reductant level sensor.
• Test the sensor's resistance and voltage.
• Replace the reductant level sensor if faulty.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the control module if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $400
Moderate
• Ford F-250
• Chevrolet Silverado
• Ram 2500
• Regularly check and maintain reductant fluid levels.
• Inspect wiring and connectors for damage.
• Use quality reductant fluid.
Sensor Issue
• Do not ignore the check engine light.
• Regularly service the vehicle's emission system.
• Consult a professional mechanic for diagnosis.
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code has become more common with the increased use of SCR systems in diesel vehicles to meet emissions standards.
Moderate – While the vehicle may still operate, emissions and performance may be affected.
Driving with a malfunctioning emissions system may not comply with environmental regulations.
• Engine running
• Vehicle at operating temperature
The reductant level sensor is typically located in or near the reductant tank, often at the rear of the vehicle.
Q: Can I drive with a P21AE code?
A: You can drive, but it's best to fix the issue soon to avoid increased emissions and potential engine performance issues.
Q: What is reductant fluid?
A: Reductant fluid, often called Diesel Exhaust Fluid (DEF), is used in diesel engines to reduce harmful emissions.
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