Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the car's computer has detected a problem with the heater that keeps a special fluid warm. The fluid helps clean the car's exhaust. It's like when a heater in your house isn't working right.
The P20C8 code is triggered when the Engine Control Module (ECM) detects a high voltage condition in the control circuit for the reductant heater D.
The reductant heater is part of the vehicle's Selective Catalytic Reduction (SCR) system, which reduces emissions by injecting a urea-based fluid into the exhaust. Heater D is one of several heaters that ensure the fluid doesn't freeze in cold temperatures. A 'circuit high' condition indicates excessive voltage, which could be due to a short circuit or a malfunctioning component.
• Check Engine Light is on
• Possible reduction in fuel efficiency
• Increased emissions
• Faulty reductant heater D
• Open or shorted wiring in the heater circuit
• Faulty ECM
Reductant: A fluid used in SCR systems to reduce emissions.
SCR: Selective Catalytic Reduction, a system used to reduce vehicle emissions.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for damage or corrosion.
• Test the reductant heater D for proper resistance and operation.
• Replace the faulty reductant heater D.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$200 - $600
Moderate
• Ford F-250
• Chevrolet Silverado
• Ram 2500
• Regularly inspect the SCR system components.
• Ensure proper maintenance of the vehicle's electrical system.
• Use high-quality reductant fluid.
Sensor Issue
• Do not ignore the Check Engine Light.
• Seek professional diagnostics to prevent further damage.
Check with the vehicle manufacturer for warranty coverage on emission-related components.
This code has become more common with the increased use of SCR systems in diesel vehicles to meet emission standards.
Moderate – While the vehicle may still operate, emissions and fuel efficiency could be affected.
Operating a vehicle with malfunctioning emission systems may violate environmental regulations.
• Engine running at normal operating temperature
• Ambient temperature above freezing
The reductant heater is typically located near the DEF (Diesel Exhaust Fluid) tank or lines.
Q: Can I drive with a P20C8 code?
A: While you may be able to drive, it's not recommended as it can lead to increased emissions and reduced fuel efficiency.
Q: How do I reset the P20C8 code?
A: After repairs, use an OBD-II scanner to clear the code. If the issue is resolved, the code should not return.
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