AutoCodes – Generic – P21AA

P21AA Code - Reductant Level Sensor 2 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 2, Reductant Level Sensor 2 harness is open or shorted, Reductant Level Sensor 2 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: P21AA indicates Reductant Level Sensor 2 Circuit Low Voltage.
Common causes: Common causes include Faulty Reductant Level Sensor 2, Reductant Level Sensor 2 harness is open or shorted, Reductant Level Sensor 2 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 1,365

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 P21AA 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 P21AA - Reductant Level Sensor 2 Circuit Low Voltage - AutoCodes.com — P21AA Code - Reductant Level Sensor 2 Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P21AA?

Faulty Reductant Level Sensor 2
Reductant Level Sensor 2 harness is open or shorted
Reductant Level Sensor 2 circuit poor electrical connection

How to Fix the DTC P21AA?

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 P21AA 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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Information for Specific Makes

P21AA Chevrolet — Reductant Level Sensor 2 Circuit Low Voltage
P21AA GMC — Reductant Level Sensor 2 Circuit Low Voltage

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 P21AA Code

1. What are the common symptoms of OBDII code P21AA (Reductant Level Sensor 2 Circuit Low Voltage)?

- Common symptoms include the check engine light illuminating, reduced engine performance, and potential failure to pass emissions testing.

2. What can cause the OBDII code P21AA to trigger?

- The code P21AA can be triggered by issues such as a faulty reductant level sensor, damaged wiring in the sensor circuit, or a low voltage signal detected by the sensor.

3. How serious is the OBDII code P21AA (Reductant Level Sensor 2 Circuit Low Voltage)?

- While the code may not cause immediate harm to the vehicle, it can lead to decreased fuel efficiency and increased emissions, which may impact the overall performance of the vehicle.

4. Can I continue driving with the OBDII code P21AA present?

- It is not recommended to continue driving with the P21AA code present, as it may lead to further issues with the vehicle's emissions system and overall performance.

5. How can I diagnose the OBDII code P21AA?

- Diagnosing the P21AA code typically involves using a scan tool to retrieve the specific fault code, testing the reductant level sensor and its circuit for proper operation, and checking for any wiring or connection issues.

6. What are the repair options for fixing the OBDII code P21AA?

- Repair options for the P21AA code may include replacing the reductant level sensor, repairing or replacing damaged wiring in the sensor circuit, or resetting the code after addressing any underlying issues.

7. Can I reset the OBDII code P21AA without fixing the underlying issue?

- While you can reset the code using a scan tool, it is important to address the underlying issue causing the P21AA code to prevent further problems with the vehicle's emissions system.

8. How much does it cost to repair the OBDII code P21AA?

- The cost of repairing the P21AA code can vary depending on the specific issue causing the fault, the labor rates in your area, and whether you choose to do the repairs yourself or take your vehicle to a mechanic.

9. Is the OBDII code P21AA a common issue in certain vehicle models?

- The P21AA code may be more common in vehicles equipped with reductant level sensors, such as diesel-powered vehicles with selective catalytic reduction (SCR) systems.

10. How can I prevent the OBDII code P21AA from recurring in the future?

- To prevent the P21AA code from recurring, it is important to perform regular maintenance on your vehicle, address any issues with the emissions system promptly, and follow the manufacturer's recommended service schedule.