AutoCodes – Chevrolet – P21DD Chevrolet

P21DD Chevrolet Code - Reductant Heater 1 Current Too Low

Quick Answer

The Selective Catalyst Reduction (SCR) system reduces Oxides of Nitrogen (NOx) emissions by injecting a metered amount of Diesel Exhaust Fluid (DEF) or reductant into the exhaust gas stream entering the SCR catalyst. Common causes include Faulty Reductant Heater 1, Reductant Heater 1 harness is open or shorted, Reductant Heater 1 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: P21DD Chevrolet indicates Reductant Heater 1 Current Too Low.
Common causes: Common causes include Faulty Reductant Heater 1, Reductant Heater 1 harness is open or shorted, Reductant Heater 1 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 3,266

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

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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 P21DD Chevrolet Description

The Selective Catalyst Reduction (SCR) system reduces Oxides of Nitrogen (NOx) emissions by injecting a metered amount of Diesel Exhaust Fluid (DEF) or reductant into the exhaust gas stream entering the SCR catalyst. Within the SCR catalyst, the reductant reacts with the NOx to form nitrogen, carbon dioxide, and water vapor. Upstream and downstream NOx sensors provide the Engine Control Module (ECM) with engine-out and tailpipe-out NOx levels in Parts Per Million (ppm). The ECM then adjusts the amount of reductant injected upstream of the SCR based on the NOx concentration. Engine-out NOx levels as measured by NOx Sensor 1 will either increase (high ppm) or decrease (low ppm) the amount of reductant injected. The NOx concentration as measured by NOx Sensor 2 provides the ECM with both an indication of the NOx conversion efficiency within the SCR as well as confirming the proper operation of the reductant system. The Diagnostic Trouble Code (DTC) will be set when the Glow Plug Control Module (GPCM) detects a heater open circuit by detecting a low current in the heater.

OBDII Code P21DD Chevrolet - Reductant Heater 1 Current Too Low - AutoCodes.com — P21DD Chevrolet Code - Reductant Heater 1 Current Too Low

What does this mean?

What are the Possible Causes of the DTC P21DD Chevrolet?

Faulty Reductant Heater 1
Reductant Heater 1 harness is open or shorted
Reductant Heater 1 circuit poor electrical connection
Faulty Glow Plug Control Module (GPCM)

How to Fix the DTC P21DD Chevrolet?

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 P21DD Chevrolet 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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Need Help with the Code?

Get the P21DD Chevrolet code diagnosed by a professional: Find a repair shop in your area

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 P21DD Chevrolet Code

1. What are the common symptoms of OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low)?

Symptoms may include the Check Engine Light (CEL) illuminating, reduced engine performance, and potential failure to pass emissions testing.

2. What are the possible causes of OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low)?

Potential causes include a faulty reductant heater 1, wiring issues, a defective reductant heater control module, or a software issue.

3. How can I diagnose OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low)?

Diagnosis typically involves using an OBDII scanner to read the code, inspecting the reductant heater system components for damage, checking the wiring for continuity, and testing the reductant heater resistance.

4. Can I continue driving with OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low) present?

It is generally not recommended to continue driving with this code as it can lead to reduced engine performance and potential damage to the emissions control system.

5. How can I repair OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low)?

Repair options may include replacing the faulty reductant heater 1, repairing damaged wiring, replacing the reductant heater control module, or updating the software as recommended by the manufacturer.

6. Will OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low) cause any long-term damage to the vehicle?

Continued driving with this code unresolved can potentially cause damage to the emissions control system and may lead to more costly repairs in the future.

7. How much does it typically cost to repair OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low)?

Repair costs can vary depending on the specific cause of the issue, but it is advisable to consult with a professional mechanic for an accurate diagnosis and cost estimate.

8. Can a DIY enthusiast fix OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low)?

While some experienced DIY enthusiasts may be able to address this issue, it is recommended to seek professional help to ensure proper diagnosis and repair of the reductant heater system.

9. Is OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low) a common problem in Chevrolet vehicles?

This code is not as common as some other OBDII codes, but it can still occur in Chevrolet vehicles equipped with a reductant heater system.

10. How frequently should I have the reductant heater system checked to prevent OBDII code P21DD Chevrolet (Reductant Heater 1 Current Too Low)?

Regular maintenance checks as per the manufacturer's recommendations can help prevent issues with the reductant heater system and avoid triggering the P21DD code.