What Is p21d Code On Duramax – How To Fix?

Duramax diesel engines are known for their robustness and performance. However, there is one potential issue with these engines that consumers need to be aware of- the p21dd code Duramax.

The p21dd code indicates a problem with the tank heater and can lead to reduced fuel efficiency and even engine failure.

Duramax DEF tank heaters are a common issue on many diesel trucks. When the heater fails, it can cause the truck to overheat and potentially catch on fire.

If you experience any of these symptoms, make sure to bring your vehicle in for inspection.

p21dd code Duramax

What Does P21dd Code Mean On Duramax?

P21dd code indicates a problem with the diesel engine and is typically displayed on DEF (diesel engine Fuel) heaters. If your DEF tank heater is displaying this code, there is likely a problem with the engine.

In most cases, fixing the issue will require a mechanic to replace the engine. If you are unable to fix the issue yourself, please contact your local dealer.

If your DEF tank heater is not functioning, it may be because of an issue with the code.

To determine the cause, you will need to access the vehicle’s OBD II diagnostic port and scan for codes. If there are any P21dd codes present, your heater may not be functioning properly.

How serious is the P21dd Code on Duramax?

When the P21dd code is set, it means there is a problem with the tank heater.

The seriousness of the code depends on a variety of factors, including the make and model of the engine.

But in general, a P21dd code indicates a serious engine problem that needs to be fixed as soon as possible.

 If you’ve ever given a P21dd code, don’t ignore it – take your engine to a mechanic as soon as possible to get it fixed.

What are the symptoms of the P21dd Code?

Duramax engines are known for their robustness and performance, but they can also be susceptible to several issues.

  • One such issue is insufficient current draw from the reductant tank heater.

When this happens, the engine can experience

  • Reduced performance
  • Increased emissions,
  • And even possible damage.

To avoid these problems, it is important to know what the symptoms of an insufficient current draw from the reductant tank heater are and how to fix them.

The glow plug control module (GPCM) can detect:

  • Insufficient current draw from the reductant tank heater, which sets the P21dd code.
  • Problem with the glow plug control system and requires immediate attention.

If the glow plugs do not light, this could be an indication of a cracked or broken glow plug wire.

The Causing Factors of the Error CodeP21dd

  • P21dd code is set when the GPCM detects insufficient current draw from the reductant tank heater.
  • The glow plug control module (GPCM) shuts off the glow plugs to prevent overheating and reduce fuel flow to the engine.
  • P21dd code can be caused by many factors, such as a disconnected
  • Malfunctioning GPCM,
  • A clogged reductant tank, or a faulty glow plug relay.

How do I fix my Duramax P21dd Code?

Hello, if you’re experiencing an issue with your Duramax P21dd code, the issue is likely related to one or more of the following:

  • A bad O-ring,
  • A bad shield,
  • Or something blocking airflow into or out of the engine.

To fix the code, you’ll need to

  • Remove the shield and then remove the tank.
  • Install new O-rings and clear the code before the testing drive to see if it fixes the problem.

But before testing the fix, it is important to ensure that everything is in working order.

Once the code has been cleared, it is important to drive the vehicle to see if the issue has been resolved.

How Much Does It Cost To Solve P21dd Code Duramax?

P21dd is a code that indicates a problem with the engine’s Duramax turbocharger.

If you’re experiencing this code, it’s important to find a mechanic who can diagnose and fix the issue.

Depending on the severity of the problem, it can cost anywhere from $500 to $5,000 to get your engine running properly again.

There are a few different ways to solve the p21dd code on a Duramax diesel engine. The most common is to use a scan tool to identify and correct the error.

Common Mistakes When Diagnosing the P21dd Code Duramax

When diagnosing a P21dd code on a Duramax engine, there are a few common mistakes that can be made.

Many times, the code is caused by an issue with the turbocharger or fuel injectors. But other times it can be due to something as simple as a loose connection.

Here are four mistakes that you should avoid when diagnosing this code:

  • Ignoring the check engine light (CEL)
  • Testing the engine without the fuel system isolated
  • Not using an accurate scan tool
  • Not having a thorough understanding of the codes so that the correct repairs can be made.

people also ask (FAQ)

1. What is a reductant tank heater?

Control Circuit Low for Reductant Tank Heater OBD-II Code P202B. A Diesel Particulate Filter is used to minimize soot emissions in newer diesel automobiles. DEF Fluid is used in this filter to aid in the removal of soot. Heating the DEF Fluid with the Reductant Tank Heater results in more efficient use of energy.

2. What is a def heater?

Heating Pots for DEF provide adequate flow thru the pipes and pumping unit by immediately returning DEF to liquid condition. A malfunctioning DEF heating element is a typical cause of a diesel vehicle running in limp mode or not at full power.

3. How many gallons Duramax DEF tank?

In cars with Duramax LML engines, the DEF tank holds around 5 gallons of DEF and is intended to provide 5,000 miles of travel before it has to be refilled.

4. How do you know if your DEF fluid is bad?

You can tell whether your DEF is awful just by looking at it. A tainted or aged fluid will look hazy or tinted since the fluid is normally clear. Small particles, as well as bigger boulders and dirt, may be easily seen. Keep out of reach of children and animals.

5. Is a DEF heater necessary?

DEF tank warmers are a need for individuals who use and rely on DEF. ‘ Use, transportation, storage, or provisioning for others all need careful consideration and awareness when it comes to DEF.

Watch >> How to repair code P21DD in 2013 Duramax

Final Words

The p21dd code Duramax is a problem with the Duramax diesel engine.

If your truck experiences this issue, have it towed to a dealership for repairs. Be sure to keep an eye on your coolant levels, as they may be low due to the engine overheating.

If you are experiencing any of the symptoms associated with the code, take your vehicle to a mechanic for diagnosis and repair.

Don’t wait until the problem gets worse – prevention is always the best course of action.

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Who Worked on This post?



Anderson is an experienced auto mechanic with over 10 years in the industry. He is skilled in diagnosing and repairing a wide range of vehicles, from sedans to trucks and SUV

Syed Ahmed


Syed Ahmed has been working as an auto mechanic editor for the past five years. He has a background in mechanical engineering and a love for all things automotive

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