Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means there's a problem with the heater that helps a special fluid called DEF (Diesel Exhaust Fluid) work properly in your car. The heater might be getting too much electricity.
The P20BC code indicates that the control circuit for the reductant heater 'A' is experiencing a high voltage condition. This can be caused by issues such as a short circuit or a malfunctioning control module.
The reductant heater is part of the Selective Catalytic Reduction (SCR) system in diesel engines. It ensures that the Diesel Exhaust Fluid (DEF) remains at the optimal temperature for effective emission reduction. A 'high' condition in the control circuit suggests excessive voltage, potentially due to wiring issues, a faulty heater, or a malfunctioning control module.
• Check Engine Light is on
• Poor engine performance
• Increased emissions
• Faulty reductant heater
• Short circuit in the wiring
• Malfunctioning control module
DEF: Diesel Exhaust Fluid, a fluid used in SCR systems to reduce emissions.
SCR: Selective Catalytic Reduction, a system in diesel engines to reduce emissions.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for damage or corrosion.
• Test the reductant heater for proper operation.
• Replace the faulty reductant heater.
• Repair or replace damaged wiring.
• Replace the control module if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$200 - $600
Moderate
• Ford F-Series
• Chevrolet Silverado
• Ram 2500
• Regularly inspect the DEF system components.
• Ensure proper maintenance of the vehicle's electrical system.
• Use high-quality DEF fluid.
Sensor Issue
• Have the vehicle inspected by a professional if the Check Engine Light comes on.
• Avoid ignoring the issue as it can lead to increased emissions.
• Regular maintenance can prevent such issues.
Check with your vehicle manufacturer for warranty coverage on emissions-related components.
This code has become more common with the increased use of SCR systems in diesel vehicles to meet emission standards.
Moderate – It should be addressed soon to prevent increased emissions and potential engine performance issues.
Ignoring emission-related codes can lead to failing emissions tests and may not comply with local environmental regulations.
• Engine running
• DEF system active
The reductant heater is typically located near the DEF tank or within the SCR system.
Q: Can I drive with a P20BC code?
A: It's possible to drive, but it's not recommended as it may lead to increased emissions and potential engine performance issues.
Q: What is a reductant heater?
A: A reductant heater keeps the DEF fluid at the right temperature to ensure it works properly in reducing emissions.
High-End · Full-system diagnostics
A full-system bidirectional platform aimed at advanced DIY users and professional diagnostic workflows.
Network faults often require full-system access instead of a generic code reader alone.
View on Amazon
Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
View on Amazon
Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
View on AmazonThese are optional diagnostic tools, not guaranteed fixes. As an Amazon Associate I earn from qualifying purchases.