P20B2 DTC Code: Understanding the Fault and Fixing It


The P20B2 DTC code is commonly encountered in vehicles, indicating a specific issue related to the reductant heater “A” control circuit low. This diagnostic trouble code (DTC) can often be confusing for vehicle owners, as they may not be familiar with the technical jargon associated with it. In this comprehensive article, we will delve into the details of the P20B2 code, what it signifies, the potential causes behind it, and the recommended steps for resolving it.

Understanding the P20B2 DTC Code

The P20B2 DTC code is a specific fault code used in the automotive industry to identify issues with the reductant heater “A” control circuit. In vehicles equipped with selective catalytic reduction (SCR) systems, this code becomes relevant as it highlights a problem in one of the components responsible for reducing harmful emissions.

What Does the P20B2 DTC Code Mean?

The P20B2 code signifies that the control circuit for the reductant heater “A” is experiencing a low voltage condition. This heater is crucial for the SCR system to function optimally. The SCR system, typically found in diesel-powered vehicles, helps in converting harmful nitrogen oxides (NOx) into less harmful substances through the injection of a urea-based solution called Diesel Exhaust Fluid (DEF), also known as AdBlue.

A low voltage condition in the reductant heater control circuit “A” could affect the heater’s ability to maintain the desired temperature, leading to suboptimal performance of the SCR system, increased emissions, and potentially triggering the vehicle’s check engine light.

Potential Causes of the P20B2 DTC Code

Several factors can contribute to the appearance of the P20B2 DTC code. It is important to understand that this code is just a starting point for diagnosis, and further testing will be necessary to pinpoint the exact cause. However, common causes associated with the P20B2 code include:

  1. Faulty reductant heater “A”: The reductant heater itself may be defective, causing the control circuit to experience low voltage. This can be due to internal heating element failure or electrical component malfunctions.

  2. Wiring issues: Damaged, corroded, or shorted wiring can disrupt the flow of electrical current and lead to a low voltage condition in the control circuit.

  3. Faulty temperature sensor: The temperature sensor that measures the temperature of the reductant heater may be providing incorrect readings, leading to improper voltage control.

Diagnosing and Fixing the P20B2 DTC Code

When faced with the P20B2 DTC code, it is advisable to follow a systematic diagnostic approach to identify and resolve the underlying issue. Here are the steps you can take:

  1. Visual inspection: Begin by conducting a visual inspection of the reductant heater “A,” its wiring, and surrounding components. Look for any signs of damage, loose connections, or evident issues that might help in narrowing down potential causes.

  2. Testing the reductant heater: Connect a digital multimeter to the reductant heater “A” to measure the voltage across the control circuit. If the voltage reading is significantly lower than the expected value, it indicates a low voltage condition and a potential issue with the heater itself.

  3. Inspecting the wiring harness: Test the wiring harness for any signs of damage, corrosion, or loose connections. Repair or replace any faulty wires or connectors found.

  4. Checking the temperature sensor: Test the temperature sensor responsible for monitoring the reductant heater’s temperature. Compare the readings with the manufacturer’s specifications, and replace the sensor if it provides inaccurate measurements.

  5. Clearing the fault code: After addressing the identified issues, clear the fault code using a diagnostic scanner or by disconnecting the vehicle’s battery for a few minutes. This will reset the vehicle’s onboard computer and allow it to reevaluate the system.

Frequently Asked Questions

Q: Can I drive my vehicle with the P20B2 DTC code? A: It is generally not recommended to drive with an active DTC code, as it often indicates an ongoing issue that may lead to further damage or increased emissions. It is best to have the issue diagnosed and fixed promptly.

Q: Can a faulty reductant heater cause other problems in my vehicle? A: While a faulty reductant heater can affect the operation of the SCR system and trigger the P20B2 code, it is unlikely to cause major issues in other vehicle systems. However, it is still important to address the problem promptly to ensure optimal vehicle performance and reduce harmful emissions.

Q: Can I fix the P20B2 DTC code myself, or do I need to visit a professional mechanic? A: Fixing the P20B2 code often requires a certain level of automotive expertise and specialized tools for diagnosis and repair. Unless you have the necessary knowledge and equipment, it is recommended to seek assistance from a qualified mechanic who can accurately diagnose and resolve the issue.

In conclusion, the P20B2 DTC code indicates a low voltage condition in the reductant heater “A” control circuit. This can affect the operation of the SCR system, resulting in increased emissions and potential check engine light activation. By following a systematic diagnostic approach and addressing the possible causes mentioned earlier, you can resolve the issue and restore optimal vehicle performance.

About author


Meet Sam Mitchell, your experienced and reliable guide in the complex world of car fault codes. With a robust career spanning over 15 years as a professional car mechanic, John has the skills, knowledge, and practical experience to help you navigate car fault issues with confidence.


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