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 control pollution. It's like a valve that isn't working right, and it's important for keeping the air clean.
The P20A8 code is triggered when the engine control module (ECM) detects a low voltage or malfunction in the circuit controlling the reductant injection air pressure control valve, which is part of the vehicle's emissions system.
The reductant injection air pressure control valve is responsible for regulating the air pressure used to inject reductant (such as Diesel Exhaust Fluid) into the exhaust system to reduce emissions. A 'circuit low' condition indicates that the ECM is receiving a lower than expected voltage signal from the valve's circuit, which could be due to an electrical issue or a malfunctioning component.
• Check Engine Light is on
• Possible reduction in fuel efficiency
• Increased emissions
• Faulty reductant injection air pressure control valve
• Damaged or corroded wiring or connectors
• Faulty ECM or control module
Reductant: A substance, often Diesel Exhaust Fluid, used to reduce emissions in diesel engines.
ECM: Engine Control Module, the computer that manages engine functions.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for damage or corrosion.
• Test the reductant injection air pressure control valve for proper operation.
• Repair or replace damaged wiring or connectors.
• Replace the reductant injection air pressure control valve if faulty.
• Reprogram or replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Wrench set
$150 - $500
Moderate
• Ford F-250
• Chevrolet Silverado
• Dodge Ram 2500
• Regularly inspect and maintain the emissions system.
• Ensure proper installation of wiring and connectors.
• Use high-quality reductant fluid.
Sensor Issue
• Have the vehicle inspected by a professional mechanic.
• Avoid ignoring the Check Engine Light.
• Keep up with regular vehicle maintenance.
Emissions-related components may be covered under the vehicle's emissions warranty. Check with your manufacturer.
This code has become more common with the increased use of emissions control systems in diesel engines.
Moderate – While the vehicle may still operate, emissions will be higher, and fuel efficiency may be reduced.
Driving with a malfunctioning emissions system may violate emissions regulations and contribute to environmental pollution.
• Engine at operating temperature
• Vehicle in closed-loop mode
The reductant injection air pressure control valve is typically located near the exhaust system, often close to the diesel particulate filter or SCR catalyst.
Q: Can I drive with a P20A8 code?
A: It's possible to drive, but it's not recommended as it can lead to higher emissions and reduced fuel efficiency.
Q: How do I reset the Check Engine Light after fixing the issue?
A: Use an OBD-II scanner to clear the code after repairs are completed.
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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.
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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.
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Fitment Required · Vehicle-fitment part
Relevant when catalyst-efficiency or emissions faults persist after proper diagnosis.
Catalyst-efficiency faults sometimes point toward converter problems after proper testing.
Catalytic converters are highly vehicle-specific and should not be purchased by code alone.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.