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P205B Error Code on Duramax (Solved)

The Duramax is often lauded as one of the most efficient Diesel engines out there. The 3.0L version, for example, achieves 95% of peak torque even at meager rotations per minute (RPM) of 1,250. However, it’s far from perfect, and error codes such as P205B prove that. 

The P205B Code is produced on the Duramax when the Powertrain Control Module senses abnormal behavior on the reductant tank temperature sensor circuit. The module cannot properly regulate your vehicle’s emission when this component is faulty.

This article will explain what causes the P205B code on Duramax and provide steps for finding and replacing the faulty part. Let’s get into it.

Causes of P205B Code on Duramax

Wiring problems, faulty reductant tank sensors, and programming issues can cause a P205B code on a Duramax engine.

A malfunctioning PCM can also cause this error code to appear. The PCM monitors multiple factors, including the exhaust, cooling, and engine speed.

Here’s an in-depth explanation of these potential causes:

  • A damaged reductant tank sensor will send false readings, which can directly affect the engine’s exhaust. These sensors can be damaged by corrosion, rough driving, and natural wear. Once the sensor is damaged, it won’t manage the exhaust properly, which can alter the engine’s emissions.
  • Car Parts explains various programming issues can cause a P205B code on a Duramax engine, even if nothing is wrong mechanically. These engines are complex and use a computer to operate numerous parts, including the powertrain module. If the computer fails or malfunctions, the P205B error code will be displayed.
  • Loose or broken wires will prevent the reductant tank sensor from working properly. There’s a large network of wires connecting the sensor, the PCM, and the computer. If any of them are chewed by pests, rusted by salinity, or damaged by user error, you’ll see multiple error codes (including the P205B code).
  • A malfunctioning PCM (powertrain control module) will cause several error codes because it doesn’t monitor the powertrain’s activity properly. If the PCM can’t monitor anything, it won’t know how the exhaust is working and whether the reductant tank is lowering the emissions.

Always use the same wire gauge if you have to replace damaged wires. Not only will an incorrect wire gauge cause faulty component issues, but it can also cause fires and various other vehicle risks.

Symptoms of a P205B Code on Duramax

Reduced MPG, poor acceleration, and black smoke coming from the exhaust are the three most common symptoms of a P205B error code on a Duramax engine. You might also notice additional error codes due to reduced fuel economy and dirtier engine parts.

Let’s break down each of these symptoms below.

  • Black smoke is a common symptom of a P205B code because the vehicle can no longer control its emissions. The exhaust is loaded with chemicals, including nitrogen oxide. These chemicals burn and turn the smoke black, which doesn’t happen if the reductant tank is working properly.
  • OBD Codes reports a P205B code can cause reduced engine performance. This means you won’t be able to accelerate as quickly, nor will you get as much power out of the engine. Once the power train stops working as it should and the P205B code displays, your truck won’t function the same.
  • You’ll notice your vehicle’s fuel economy suffers severely. Dirty emissions and black smoke can hinder the engine, making it burn fuel less efficiently. If you recently noticed a P205B code, keep an eye on the MPG (miles per gallon) during your regular commute. If it’s significantly reduced, you’ll need to find a solution as soon as possible.

Note: Some P205B codes don’t have any symptoms for a while. Your vehicle’s computer might’ve had a minor hiccup that shows incorrect error codes. While nothing bad will happen in this scenario, it’s a good idea to use an engine diagnostics tool to reset the error code. If the code comes back, it’s time to find the cause.

How to Fix P205B Code on Duramax

Fixing the P205B code can be a bit complicated for the average person, so I recommend hiring an expert if you don’t know your way around car engines. But for the experienced car repair and maintenance DIYer, it’s definitely doable. 

Here’s how to go about it: 

1. Locate the Tank and Take Out the Connections

The first step is to turn off the car. Working on your vehicle with electric currents flowing is dangerous. 

Once the car is off, locate the diesel engine’s reductant tank. The tank’s location may vary with your vehicle’s model, but most have it on the underside. If you can’t find it, check your vehicle’s user manual or perform a quick search online. 

The first thing you should do when you find the tank is to remove the hose to gain better access to the sensor. The hose can be removed using hose clamp pliers.

You may have to remove it from the back of the engine using your hands. There may be remaining fluid exiting from the hose, so keep your distance.

2. Take Out the Tank and Lay it on Flat Surface

Make it easier to access by removing the bolts that keep the tank in place. Normally, they are 13 millimeters (0.5 in), so unscrew them using a 13 mm (0.5 in) extractor. 

With the bolts out of the way, you can pull the tank downwards. You may notice it’s still connected to the rest of the engine via connector wires. Take it out. The connector tabs are found at the back of the connector heads. 

Take your tank to a flat surface so you can further examine it. You may notice that a lot of sensors are connected to it. You will have to take these out. Begin by removing the protective covering found on top of the tank. 

3. Remove Sensors and Tank Lid

Once done, unhook the sensors attached to the tank. Remember to unhook from the head and not the wire, as you may damage the wire unintentionally. Use a blower to remove some of the particulates on top of the tank. 

On top of the tank lid is a sensor attached by bolts. Use a bolt extractor to take the bolts out and remove the sensor. Remove the attached sensor wires. 

By now, you should have access to the tank lid. Opening the tank lid with your hands is extremely difficult, so you might want to use a hammer and a piece of metal. Angle the metal diagonally from the lid towards you and use the hammer to bang on the metal side facing you. 

This allows you to transfer the force of the hammer onto the metal and the lid, opening it. Beneath the lid is the seal, which you should also remove.

4. Replace the Heater Component

Use your blower to remove particulates. Pull out the component below the lid. There may still be some connector wires attached to it. This is the heater you might have to replace. 

Take out your replacement and place it in. It should come with a replacement seal as well. The replacement should easily lock in place.

When it does, place the replacement seal on top and seal the tank. You can use the old lid to close it completely. 

5. Replace the Sensor Component

Follow the same hammer tip to close the lid. Get the replacement nuts and bolts in, including the O-rings. Line the holes up and place the replacement sensor on top.

Screw in the bolts to make sure the sensor is firmly attached. Once done, you can place the protective cover back. 

6. Reposition the Newly Replaced Tank

Re-hook all connector wires on top of the tank. When you’re done, you can take the entire tank back into the engine.

Re-attach all of the connector wires you had taken out earlier. Re-screw the bolts you had taken out when you took out the tank and placed the hose back. 

7. Install Replacements Using Software Tool

You’ll have to install your replacements using a software tool such as Zeus. Start by clicking on the Codes Menu. Click on Display Codes. Click on DTC Display. From there, it should show the P205B Code and a brief explanation of it. 

Go back and click on Clear Codes. Expect your vehicle to signal that the tank is empty since the software installation is still not done. Click on Output Controls. Click on Relevel Reset. Wait for the process to finish. When it’s done, the light should be cleared. 

Confirm if the problem is solved by going to DTC Display under Display Codes under the Codes Menu. Ideally, all codes should have cleared. 

Take out your vehicle for a spin. If there are no more lights, park it and open your software tool again. Check to see if there are codes. If there are none, you should be good to go.


The P205B code is generally easy to diagnose because the engine cannot properly operate if the reductant tank temperature sensor is faulty.

The fix, however, may require more effort and know-how than regular car maintenance. The good news is that you might not have to do it again if you use the right replacement parts.