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Engine-Codes – Generic – P21AF

P21AF Code - Reductant Level Sensor 3 Circuit Low Voltage

Quick Answer

The P21AF diagnostic trouble code (DTC) indicates a problem with the Reductant Level Sensor 3 Circuit Low Voltage in a vehicle's Selective Catalytic Reduction (SCR) system. Common causes include Faulty Reductant Level Sensor 3, Wiring or connection issues in the sensor circuit, Corrosion or damage to the sensor or its connectors. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P21AF indicates Reductant Level Sensor 3 Circuit Low Voltage.
Common causes
Common causes include Faulty Reductant Level Sensor 3, Wiring or connection issues in the sensor circuit, Corrosion or damage to the sensor or its connectors.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 09, 2024
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Code P21AF Description

The P21AF diagnostic trouble code (DTC) indicates a problem with the Reductant Level Sensor 3 Circuit Low Voltage in a vehicle's Selective Catalytic Reduction (SCR) system. The SCR system is an emissions control technology that uses a urea-based solution, known as diesel exhaust fluid (DEF), to reduce harmful nitrogen oxides (NOx) emissions from the vehicle's exhaust. The Reductant Level Sensor 3 is responsible for monitoring the level of DEF in the tank and sending this information to the engine control module (ECM) for proper dosing.

OBDII Code P21AF - Reductant Level Sensor 3 Circuit Low Voltage
P21AF Code - Reductant Level Sensor 3 Circuit Low Voltage

Common Causes of P21AF

  1. Faulty Reductant Level Sensor 3
  2. Wiring or connection issues in the sensor circuit
  3. Corrosion or damage to the sensor or its connectors
  4. Low DEF fluid level in the tank
  5. ECM software or hardware issues

Symptoms of P21AF

  1. Check Engine Light illuminated on the dashboard
  2. Reduced fuel efficiency
  3. Poor engine performance or rough idling
  4. Failed emissions test due to increased NOx emissions
  5. Vehicle going into limp mode to protect the engine from potential damage

How to Fix P21AF

  1. Perform a visual inspection of the Reductant Level Sensor 3 and its wiring for any visible damage or corrosion.
  2. Test the sensor's resistance and voltage output using a multimeter to determine if it is functioning correctly.
  3. Check the DEF fluid level in the tank and refill if necessary.
  4. Clear the DTC from the ECM's memory using a scan tool and monitor the system for any recurring issues.
  5. If the problem persists, consider replacing the Reductant Level Sensor 3 or addressing any underlying wiring or ECM issues.

Cost to Fix P21AF

The cost of repairing a P21AF DTC related to the Reductant Level Sensor 3 Circuit Low Voltage can vary depending on the specific vehicle make and model, as well as the extent of the repair needed. In general, replacing the sensor itself can range from $150 to $300, not including labor costs. Labor rates at auto repair shops typically range from $80 to $150 per hour, so the total repair cost could be around $250 to $450. It's essential to consult with a certified mechanic or dealership to obtain an accurate cost estimate based on your vehicle's specific requirements.

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Code P21AF Information for Specific Makes

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P21AF Code

1. What are the common symptoms of OBDII code P21AF (Reductant Level Sensor 3 Circuit Low Voltage)?

The common symptoms of P21AF include the check engine light illuminating, reduced engine performance, and potential issues with the vehicle's emissions system.

2. What are the possible causes of OBDII code P21AF?

Possible causes of P21AF include a faulty reductant level sensor, wiring issues in the circuit, poor electrical connections, or a malfunctioning engine control module.

3. How serious is OBDII code P21AF (Reductant Level Sensor 3 Circuit Low Voltage)?

While the severity may vary, it is important to address P21AF promptly to prevent potential damage to the emissions system and ensure the vehicle meets environmental standards.

4. Can I continue driving with OBDII code P21AF active?

It is not recommended to drive with an active P21AF code, as it may lead to increased emissions, reduced fuel efficiency, and possible engine performance issues.

5. How can I diagnose OBDII code P21AF at home?

You can diagnose P21AF using an OBDII scanner to retrieve the code, inspecting the reductant level sensor and its wiring for any visible damage, and testing the sensor's voltage to determine if it falls within the specified range.

6. What are some repair tips for fixing OBDII code P21AF?

Repair tips for P21AF may include replacing the reductant level sensor, repairing any damaged wiring or connectors, ensuring proper sensor calibration, and clearing the code using an OBDII scanner.

7. How much does it typically cost to repair OBDII code P21AF?

The cost of repairing P21AF can vary depending on the extent of the issue, the parts needed, and whether you choose to do the repairs yourself or seek professional help. Costs may range from a few hundred to over a thousand dollars.

8. Can weather or environmental factors trigger OBDII code P21AF?

Extreme weather conditions or exposure to water and contaminants can potentially impact the reductant level sensor and trigger P21AF. It is essential to ensure the sensor is properly sealed and protected.

9. Will OBDII code P21AF cause my vehicle to fail an emissions test?

Yes, an active P21AF code can result in a failed emissions test due to issues with the reductant level sensor affecting the vehicle's emissions control system.

10. How can I prevent OBDII code P21AF from recurring in the future?

To prevent P21AF from recurring, it is essential to perform regular maintenance on the emissions system, keep the reductant level sensor and its components clean and free from damage, and address any related issues promptly.

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