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 part of the car that helps keep the special fluid used to reduce pollution warm. It's like when your electric blanket gets too hot and stops working right.
The P20B8 code indicates that the vehicle's computer has detected a high voltage condition in the circuit that controls the heater for the reductant metering unit. This heater is responsible for keeping the diesel exhaust fluid (DEF) at the right temperature.
The reductant metering unit is part of the Selective Catalytic Reduction (SCR) system in diesel engines. It injects DEF into the exhaust stream to reduce nitrogen oxide emissions. The heater ensures the DEF doesn't freeze in cold temperatures. A high circuit condition means there's excessive voltage, which could indicate a wiring issue or a problem with the heater itself.
• Check Engine Light illuminated
• Possible reduction in engine performance
• Increased emissions
• Faulty reductant metering unit heater
• Wiring issues such as short circuits or open circuits
• Faulty control module
Reductant: A substance that reduces emissions in the exhaust system.
SCR: Selective Catalytic Reduction, a system used to reduce nitrogen oxides in diesel exhaust.
• Use an OBD-II scanner to confirm the code.
• Inspect wiring and connectors for damage or corrosion.
• Test the reductant metering unit heater for proper operation.
• Repair or replace damaged wiring or connectors.
• Replace the reductant metering unit heater if faulty.
• Reset the OBD-II codes and test drive the vehicle to ensure the issue is resolved.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $500
Moderate
• Ford F-250
• Chevrolet Silverado 2500HD
• Ram 2500
• Regularly inspect wiring and connectors for damage.
• Ensure DEF system maintenance is performed as scheduled.
• Avoid using low-quality DEF.
Sensor Issue
• Address the issue promptly to avoid increased emissions.
• Consult a professional mechanic if unsure about repairs.
Check with the vehicle manufacturer for warranty coverage on emission-related components.
This code is relatively common in diesel vehicles equipped with SCR systems, especially in colder climates where DEF freezing is a concern.
Moderate – While the vehicle may still operate, emissions may increase, and performance could be affected.
Driving with increased emissions may violate environmental regulations. Ensure repairs are made to comply with emission standards.
• Engine at operating temperature
• Cold ambient temperatures to test heater function
The reductant metering unit is typically located near the DEF tank or along the exhaust system.
Q: Can I drive with a P20B8 code?
A: You can drive, but it's best to fix the issue soon to avoid increased emissions and potential performance issues.
Q: What happens if I ignore this code?
A: Ignoring the code can lead to higher emissions, potential engine performance issues, and may fail emissions testing.
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