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 is getting a weak signal from a part that checks the quality of a special fluid used to reduce pollution.
The P21CD code is triggered when the Engine Control Module (ECM) detects a low voltage condition in the Reductant Quality Module, which is responsible for monitoring the quality of the diesel exhaust fluid (DEF).
The Reductant Quality Module is a component in diesel engines that monitors the quality of the diesel exhaust fluid (DEF), which is used to reduce nitrogen oxide emissions. A low supply voltage to this module can indicate issues with the power supply, wiring, or the module itself, leading to potential inefficiencies in emission control.
• Check Engine Light is on
• Possible reduction in engine performance
• Increased exhaust emissions
• Faulty Reductant Quality Module
• Poor electrical connection
• Blown fuse or relay in the circuit
Reductant: A substance used to reduce nitrogen oxide emissions in diesel engines.
DEF: Diesel Exhaust Fluid, a liquid used in diesel engines to reduce emissions.
• Check the vehicle's battery and charging system.
• Inspect the wiring and connectors to the Reductant Quality Module.
• Test the Reductant Quality Module for proper operation.
• Replace or repair faulty wiring or connectors.
• Replace the Reductant Quality Module if defective.
• Ensure the battery and charging system are functioning properly.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $400
Moderate
• Ford F-250
• Chevrolet Silverado
• Dodge Ram 2500
• Regularly check and maintain the vehicle's electrical system.
• Ensure quality diesel exhaust fluid is used.
• Perform routine inspections of the vehicle's emission control components.
Sensor Issue
• Do not ignore the Check Engine Light.
• Have the vehicle inspected by a professional mechanic.
• Ensure the vehicle's battery is in good condition.
Check with the vehicle manufacturer for specific warranty coverage on emission-related components.
This code has been more common in diesel vehicles due to the complexity of emission control systems.
Moderate – While the vehicle may still operate, emission control efficiency may be compromised.
Driving with a malfunctioning emission control system may lead to higher emissions, which can be illegal in some areas.
• Vehicle at operating temperature
• Engine running
The Reductant Quality Module is typically located near the DEF tank or integrated into the DEF pump assembly.
Q: Can I drive with a P21CD code?
A: It's possible to drive, but it's recommended to get it checked soon to avoid increased emissions.
Q: What happens if I ignore this code?
A: Ignoring the code can lead to higher emissions and potential damage to the emission control system.
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