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 heats up the special fluid used to clean the exhaust. It's like when a heater doesn't work properly in your house.
The P248B code indicates that the vehicle's computer has detected a high voltage condition in the circuit that monitors the reductant heater. This heater is used to warm up the diesel exhaust fluid (DEF) to ensure it works properly.
The reductant heater is an essential component of the Selective Catalytic Reduction (SCR) system in diesel engines. It ensures that the DEF is at the correct temperature to effectively reduce NOx emissions. A high circuit condition suggests an electrical fault, such as a short to voltage or an open circuit, which prevents the heater from functioning correctly.
• Check Engine Light is on
• Poor engine performance
• Increased emissions
• Faulty reductant heater
• Damaged wiring or connectors
• Faulty control module
Reductant: A substance used to reduce emissions, often referring to diesel exhaust fluid (DEF).
SCR: Selective Catalytic Reduction, a system used to reduce nitrogen oxides (NOx) emissions in diesel engines.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for damage.
• Test the reductant heater for proper operation.
• Replace the reductant heater if faulty.
• Repair or replace damaged wiring or connectors.
• Replace the control module if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$200 - $600
Moderate
• Ford F-250
• Chevrolet Silverado
• Dodge Ram 2500
• Regularly inspect wiring for damage.
• Ensure DEF system maintenance is up-to-date.
• Use quality DEF fluid.
Sensor Issue
• Avoid driving long distances until the issue is resolved.
• Consult a professional mechanic for diagnosis and repair.
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 emissions standards.
Moderate – Should be addressed soon to avoid increased emissions and potential engine performance issues.
Ignoring emissions-related issues can lead to failing emissions tests and may be illegal in some areas.
• Engine at operating temperature
• DEF system active
The reductant heater is typically located in the DEF tank or along the DEF line.
Q: Can I drive with a P248B code?
A: It's not recommended to drive for long periods with this code, as it can lead to increased emissions and potentially damage the SCR system.
Q: How do I know if my reductant heater is working?
A: A diagnostic test using a multimeter can check for proper voltage and resistance in the heater circuit.
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.