P20B9 Code: Reductant Heater “A” Control Circuit / Open

Dealing with trouble codes might sound intimidating, especially if it’s your first time encountering a particular code. However, the first step to fixing these codes is to find out what they mean. If a  P20B9 engine code registers on your scan tool, this informative guide can help you figure out what it means and what its common symptoms and causes are.

What Does the P20B9 Code Mean?

Diagnostic trouble code (DTC) P20B9 stands for “Reductant Heater “A” Control Circuit/Open.” This code sets when the reductant heater doesn’t perform as expected. The P20B9 engine code can also be triggered if the powertrain control module (PCM) doesn’t detect voltage in the reductant heater A’s control circuit. The “A” designation is used when there are multiple reductant heaters.

Powerful diesel engines have exhaust gas recirculation systems and selective catalytic reduction (SCR) systems. These SCR systems use (DEF) to convert leftover exhaust particles into harmless gasses.

To eliminate the leftover particles, the exhaust system’s temperature needs to increase. The injection of DEF into the exhaust stream brings the diesel particulate filter (DPF) up to temperature. The system is then able to break down harmful nitrogen oxide to nitrogen, carbon dioxide, and water.

The reductant catalysts are added to the exhaust system in order to further reduce leftover nitrogen oxide in the exhaust stream. The reductant heater warms the DEF tank to prevent DEF crystallization when the temperature outside the vehicle decreases.

The PCM monitors and controls the selective catalytic reduction (SCR) system. It uses input from different sensors to determine the right timing for diesel exhaust fluid (DEF) injection. If the PCM doesn’t detect any voltage from the control circuit for the reductant heater A or if the reductant heater A does not function as expected, it sets this code.

Note: The definition of code P20B9 can be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P20B9 Code?

Trouble codes, like the P20B9, can have many potential causes. Here are some of the most common triggers of the code P20B9:

• Reductant heater failure
• Open or shorted circuits in the reductant heater control
• Defective reductant temperature sensor
• Bad SCR controller/PCM
• Programming error
• Malfunctioning reductant tank heater
• Other wiring issues

What are the Common Symptoms of the P20B9 Code?

Here are some of the most common symptoms of the P20B9 engine code:

• Illuminated malfunction indicator lamp or check engine light
• Reduced engine performance
• Reduced fuel efficiency
• Excessive black smoke from the vehicle’s exhaust
• DPF regeneration might not occur
• Other SCR-related codes might set

How to Diagnose the P20B9 Code

Different trouble codes can have similar symptoms and causes. Because of this, thorough troubleshooting is required in order to fix DTCs properly and efficiently.

There are many resources you can use to find out more about the code P20B9 and how the diagnostic process goes. But of all these auto repair guides and resources, vehicle-specific repair guides are the best. These guides contain step-by-step repair information, as well as detailed diagrams and illustrations for your convenience.

If you want to learn more about P20B9 troubleshooting and repair, here are some videos that discuss these processes in more detail:

How to Fix the P20B9 Code

As mentioned above, many DTCs have multiple possible causes, and each of these causes has their own recommended solutions. In addition, different vehicle manufacturers will also have their own repair procedures. This is why there are no cure-alls for DTCs.

While it’s definitely important to address DTCs like the P20B9 as soon as possible, special tools and knowledge are needed to properly solve the problem. If you don’t have experience fixing DTCs, it’s best to leave the job to a certified mechanic.

Other Notes About P20B9

If you encounter the P20B9, you should address it as soon as possible because it’s considered a severe code. This means that your vehicle’s SCR system might get disabled because of this code. Catalyst damage can also occur. For those reasons, driving with the P20B9 engine code is not advised.

If you encounter this code, we recommend that you take your vehicle to a shop for diagnosis and repairs as soon as possible.