AutoCodes – GMC – P21AB GMC

P21AB GMC Code - Reductant Level Sensor 2 Circuit High 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: P21AB GMC indicates Reductant Level Sensor 2 Circuit High 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 2,171

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 P21AB 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 between 3.56-4.74 V for greater than 3 s. A voltage within this range indicates an open circuit.

OBDII Code P21AB GMC - Reductant Level Sensor 2 Circuit High Voltage - AutoCodes.com — P21AB GMC Code - Reductant Level Sensor 2 Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P21AB GMC?

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 P21AB 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 P21AB 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 P21AB GMC Code

1. What are the common symptoms of OBDII code P21AB GMC (Reductant Level Sensor 2 Circuit High Voltage)?

The common symptoms include the Check Engine Light (CEL) coming on, reduced engine performance, and potential difficulty starting the vehicle.

2. What are the possible causes of OBDII code P21AB GMC?

The code P21AB GMC can be triggered by issues such as a faulty Reductant Level Sensor 2, wiring problems, a damaged sensor connector, or a malfunctioning Engine Control Module (ECM).

3. How can I diagnose the cause of OBDII code P21AB GMC?

Diagnosing the code involves using a scan tool to retrieve the specific fault code, checking the wiring and connectors associated with the Reductant Level Sensor 2, and testing the sensor's resistance and voltage levels.

4. Can I drive my vehicle with OBDII code P21AB GMC?

It is not recommended to drive the vehicle with this code present, as it may lead to reduced engine performance and potential damage to the emissions control system.

5. How can I repair OBDII code P21AB GMC?

Repairing the code may involve replacing the Reductant Level Sensor 2, repairing any damaged wiring or connectors, or resetting the ECM after fixing the underlying issue.

6. Can a DIY enthusiast fix OBDII code P21AB GMC?

Depending on your experience and tools available, you may be able to diagnose and fix simpler issues related to this code. However, complex repairs or sensor replacements may require professional assistance.

7. What is the purpose of the Reductant Level Sensor 2 in the vehicle's emissions system?

The Reductant Level Sensor 2 is responsible for measuring the level of Diesel Exhaust Fluid (DEF) in the emissions system, helping to ensure proper emissions control and compliance with environmental regulations.

8. How important is it to address OBDII code P21AB GMC promptly?

It is essential to address the code promptly to prevent potential damage to the emissions system, ensure optimal engine performance, and avoid failing emission tests.

9. Are there any preventive measures to avoid OBDII code P21AB GMC in the future?

Regularly inspecting and maintaining the emissions control system, checking the DEF levels, and keeping an eye on the Check Engine Light can help prevent issues that may trigger this code.

10. What should I do if OBDII code P21AB GMC keeps recurring after repair?

If the code persists after repair, it is advisable to recheck the sensor, wiring, and connectors for any overlooked issues, or seek professional help to diagnose the underlying problem accurately.