AutoCodes – GMC – P21AF GMC

P21AF GMC Code - Reductant Level Sensor 3 Circuit Low Voltage

Quick Answer

The reductant level/temperature sensor is a solid-state device that provides the Engine Control Module (ECM) with information on reductant level and temperature. Common causes include Faulty Reductant Level Sensor 3, Reductant Level Sensor 3 harness is open or shorted, Reductant Level Sensor 3 circuit poor electrical connection. 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 GMC indicates Reductant Level Sensor 3 Circuit Low Voltage.
Common causes: Common causes include Faulty Reductant Level Sensor 3, Reductant Level Sensor 3 harness is open or shorted, Reductant Level Sensor 3 circuit poor electrical connection.
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.

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Code Popularity 459

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Sep 10, 2021

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P21AF GMC Description

The reductant level/temperature sensor is a solid-state device that provides the Engine Control Module (ECM) with information on reductant level and temperature. The level/temperature sensor receives system voltage directly from the underhood electrical center and ground through a chassis ground circuit. The level sensor consists of three sensing elements. Reductant level sensor 3 is highest, reductant level sensor 2 is located between sensors 1 and 3. Reductant level sensor 1 is located at a low reductant level. Reductant level sensor 3 is located at less than half the range of the DEF tank level. The scan tool will display Active when the level sensors are in contact with the reductant and Inactive when not in contact with the reductant. An integrated temperature sensor monitors reductant temperature. Reductant level and temperature signals are processed within the sensor and supplied to the ECM as serial data messages. The ECM will set a DTC when it detects an invalid level or temperature serial data message from the sensor. The Diagnostic Trouble Code (DTC) will be set when the ECM receives a serial data message from the reductant sensor module that the emission reduction fluid tank level sensor 1, 2, or 3 voltage is less than 0.17 V for greater than 3 s. A voltage within this range indicates a short to ground.

OBDII Code P21AF GMC - Reductant Level Sensor 3 Circuit Low Voltage - AutoCodes.com — P21AF GMC Code - Reductant Level Sensor 3 Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P21AF GMC?

Faulty Reductant Level Sensor 3
Reductant Level Sensor 3 harness is open or shorted
Reductant Level Sensor 3 circuit poor electrical connection

How to Fix the DTC P21AF GMC?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P21AF GMC code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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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 GMC Code

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

- Common symptoms include the Check Engine Light (CEL) illuminating on the dashboard, reduced engine performance, and potential issues with the vehicle's emissions system.

2. What can cause the OBDII code P21AF GMC to appear?

- The code can be triggered by a faulty reductant level sensor, wiring issues in the sensor circuit, or problems with the reductant fluid itself.

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

- While the code may not cause immediate harm to the vehicle, it can lead to increased emissions, reduced fuel efficiency, and potential failures in emissions testing.

4. Can I continue driving with the P21AF GMC code present?

- It is generally safe to drive the vehicle with this code present, but it is recommended to address the issue promptly to prevent any potential long-term problems.

5. How can I diagnose and repair the P21AF GMC code?

- Diagnosis typically involves checking the reductant level sensor, inspecting the wiring for any damage, and testing the reductant fluid quality. Repair may involve replacing the sensor, repairing wiring, or refilling the reductant fluid.

6. Will resetting the Check Engine Light make the P21AF GMC code go away?

- Simply resetting the Check Engine Light may clear the code temporarily, but if the underlying issue is not addressed, the code is likely to reappear.

7. Can a DIY enthusiast fix the P21AF GMC code themselves?

- Depending on your skill level and access to tools, some DIY enthusiasts may be able to diagnose and repair this code. However, professional assistance is recommended for accurate diagnosis and proper repair.

8. How much does it typically cost to repair the P21AF GMC code?

- The cost of repairing this code can vary depending on the underlying issue, but it may involve sensor replacement, wiring repairs, or reductant fluid refill, with costs ranging from $100 to $500 or more.

9. Are there any preventative measures to avoid the P21AF GMC code?

- Regularly checking the reductant fluid level and quality, as well as inspecting the sensor and wiring for any signs of wear or damage, can help prevent the occurrence of this code.

10. Can the P21AF GMC code affect the vehicle's overall performance?

- Yes, the code can impact the vehicle's overall performance by potentially causing reduced fuel efficiency, emission issues, and in some cases, engine performance issues.