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 part of the car that helps reduce pollution isn't getting enough power to work properly.
The reductant control module is responsible for managing the diesel exhaust fluid system, which reduces emissions. This code indicates that the module is receiving a lower voltage than expected.
The P21CB code is set when the Engine Control Module (ECM) detects that the supply voltage to the reductant control module is below the specified range. This could affect the operation of the diesel exhaust fluid system, leading to increased emissions.
• Check Engine Light is on
• Possible increase in emissions
• Potential reduction in engine performance
• Faulty reductant control module
• Wiring issues such as corroded or damaged wires
• Poor electrical connections
Reductant: A substance used to reduce emissions in diesel engines, often diesel exhaust fluid.
ECM: Engine Control Module, the computer that controls engine functions.
• Use a multimeter to check the voltage at the reductant control module.
• Inspect wiring and connectors for damage or corrosion.
• Test the battery and charging system to ensure proper voltage supply.
• Repair or replace damaged wiring or connectors.
• Replace the reductant control module if faulty.
• Ensure the battery and alternator are functioning correctly.
• Multimeter
• OBD-II scanner
• Basic hand tools
$150 - $600
Moderate
• Ford F-Series
• Chevrolet Silverado
• Dodge Ram
• Regularly inspect and maintain the vehicle's electrical system.
• Ensure all connections are clean and secure.
• Monitor the vehicle's battery health.
Electrical Issue
• Have your vehicle inspected by a professional if the Check Engine Light comes on.
• Avoid ignoring the issue as it may lead to increased emissions.
• Regular maintenance can prevent such issues.
Check with your vehicle manufacturer for specific warranty coverage on emissions-related components.
This code has been more common in vehicles with advanced emissions control systems, particularly in diesel engines.
Moderate – It's important to address this issue to ensure the emissions system functions correctly.
Ignoring emissions-related issues can lead to legal penalties and increased environmental impact.
• Engine running
• Vehicle at operating temperature
The reductant control module is typically located near the DEF (Diesel Exhaust Fluid) tank or in the engine compartment.
Q: Can I drive with a P21CB code?
A: While you may be able to drive, it's recommended to fix the issue to avoid increased emissions and potential engine performance problems.
Q: What happens if I ignore the P21CB code?
A: Ignoring the code can lead to higher emissions, potential fines, and further damage to the vehicle's emissions system.
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