Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means the car's computer can't tell how much special fluid is left in the tank that helps clean the exhaust. It's like when you can't see how much juice is left in your cup because the cup is too dark.
The P203B code is triggered when the vehicle's engine control module (ECM) detects an issue with the reductant level sensor circuit, which monitors the level of diesel exhaust fluid (DEF) in the tank.
The reductant level sensor is responsible for measuring the amount of diesel exhaust fluid (DEF) in the tank. If the sensor sends a signal that is out of the expected range or inconsistent, the ECM will set the P203B code. This can be due to electrical issues, sensor failure, or a problem with the DEF tank itself.
• Check engine light is on
• DEF warning light may be illuminated
• Possible reduction in engine performance
• Faulty reductant level sensor
• Wiring issues or poor electrical connections
• DEF tank contamination or blockage
Reductant: A substance used to reduce pollutants in the exhaust, such as diesel exhaust fluid (DEF).
DEF: Diesel Exhaust Fluid, a liquid used to reduce nitrogen oxide emissions in diesel engines.
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for damage or corrosion.
• Test the reductant level sensor for proper operation.
• Replace the reductant level sensor if faulty.
• Repair or replace damaged wiring or connectors.
• Clean or replace the DEF tank if contaminated.
• OBD-II scanner
• Multimeter
• Basic hand tools
$150 - $400
Moderate
• Ford F-250
• Chevrolet Silverado
• Ram 2500
• Regularly check and refill DEF levels.
• Inspect DEF tank and components for damage.
• Use high-quality DEF fluid.
Sensor Issue
• Do not ignore the DEF warning light.
• Schedule regular maintenance checks.
• Ensure DEF tank is clean and filled.
Check with the vehicle manufacturer; emissions-related components may be covered under warranty.
The P203B code has become more common as stricter emissions regulations have led to increased use of DEF systems in diesel vehicles.
Moderate – Address the issue soon to avoid potential engine performance problems.
Ignoring DEF system issues can lead to increased emissions and may violate emissions regulations.
• Engine running
• DEF system active
The reductant level sensor is typically located in the diesel exhaust fluid (DEF) tank, which is often mounted near the rear of the vehicle.
Q: Can I drive with a P203B code?
A: You can drive with this code, but it's best to fix it soon to avoid potential engine performance issues.
Q: What happens if I ignore the P203B code?
A: Ignoring the code can lead to reduced engine performance and increased emissions, and may eventually cause the vehicle to enter a limp mode.
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