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 a part in your car that helps control the temperature of a special fluid used to clean the exhaust. It's like a valve that isn't working right, and it's making the car's computer unhappy.
The P20B4 code is triggered when the engine control module (ECM) detects a high voltage condition in the circuit controlling the reductant heater coolant control valve.
The reductant heater coolant control valve is responsible for managing the flow of coolant to the reductant heater, which is used to maintain the proper temperature of diesel exhaust fluid (DEF). A high circuit condition suggests that there is excessive voltage being detected, possibly due to a short or open circuit.
• Check Engine Light illuminated
• Possible decrease in fuel efficiency
• Potential issues with DEF system performance
• Faulty reductant heater coolant control valve
• Wiring issues such as a short or open circuit
• Faulty ECM or control module
DEF: Diesel Exhaust Fluid, a fluid used to reduce emissions in diesel engines.
ECM: Engine Control Module, the computer that controls engine functions.
• Use an OBD-II scanner to confirm the code.
• Inspect wiring and connections to the valve for damage.
• Test the valve for proper operation and resistance.
• Replace the reductant heater coolant control valve if faulty.
• Repair or replace damaged wiring or connectors.
• Update or reprogram the ECM if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $400
Moderate
• Ford F-250
• Chevrolet Silverado
• Ram 2500
• Regular maintenance of the DEF system
• Inspect wiring and connectors periodically
• Use high-quality DEF fluid
Sensor Issue
• Address this issue promptly to avoid further damage.
• Consult a professional mechanic if unsure about repairs.
Check vehicle warranty for coverage on emissions-related components.
This code has been more common in diesel vehicles equipped with DEF systems since their introduction.
Moderate – While not immediately critical, it should be addressed to maintain vehicle efficiency and emissions compliance.
Ignoring emissions-related codes can lead to failing emissions tests and potential legal issues.
• Engine at operating temperature
• DEF system active
The reductant heater coolant control valve is typically located near the DEF tank or along the DEF fluid lines.
Q: Can I drive with a P20B4 code?
A: While the vehicle may still be drivable, it is recommended to address the issue to prevent potential emissions problems.
Q: How can I prevent this code from appearing?
A: Regular maintenance and inspections of the DEF system and its components can help prevent this code.
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