Fix P203F: Mechanic’s solutions that WORKED

The code P203F: Reductant Level Too Low indicates a fault in the vehicle’s emissions system, specifically signaling that the level of Diesel Exhaust Fluid (DEF) is too low. This situation can arise due to a variety of reasons such as a defective sensor, incorrect fluid in the tank, or electrical issues. It’s important to address this code to ensure the vehicle meets emission standards and operates efficiently.

P203F quick overview

Description	P203F: Reductant Level Too Low
Is it serious?	This code is moderately serious as it relates to the vehicle’s emissions system, but it typically does not lead to immediate vehicle breakdown.
Possible causes	– Defective reductant level sensor – Low Diesel Exhaust Fluid (DEF) level – Wrong fluid in DEF storage tank – Electrical short in sensor circuit – Damage or corrosion in sensor wiring
How to diagnose?	Check DEF Level: Inspect the Diesel Exhaust Fluid level in the storage tank. Inspect Sensor: Examine the reductant level sensor for defects. Verify Fluid Type: Ensure correct fluid is in the DEF tank. Electrical Inspection: Look for shorts in the sensor circuit. Sensor Connector Check: Ensure the connector is secure and corrosion-free. Wiring Harness Inspection: Check for damage or chafing in the wiring. Sensor Functionality Test: Test the sensor electronically, if possible. Clear and Retest: Clear the code and test drive to see if it reappears.

How to fix P203F – learn from mechanics

I looked into P203F service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Nissan

Vehicle Information: 2017 Nissan Titan XD PRO-4X 5.0L

Issue + Repair History:

• Codes: P2560, P203F, P008A.
• Fuel filter housing under the bed was leaking.
• Difficulty in decoding the vehicle VIN.

Suggestions to Fix Issue:

• Consult Identifix for detailed information and TSBs related to the codes.
• Verify access to service manuals and use a capable scan tool.
• Address the fuel filter housing leak as a priority.
• Consider accessing AllData DIY site for specific vehicle information.

Final Fix:

• Replaced the entire filter housing, resolving the issues.

Case #2: Ford

Vehicle Information: 2018 Ford F-350 Super Duty 6.7L

Issue + Repair History: Check Engine Light (CEL) on with a P203F code. No previous repairs related to this issue.

Suggestions to Fix Issue:

• Check the Diesel Exhaust Fluid (DEF) level in the storage tank.
• Inspect the reductant level sensor for defects.
• Ensure there is no wrong fluid in the DEF storage tank.
• Look for any electrical shorts related to the sensor.

Final Fix: The problem was resolved by topping up the DEF tank and resetting the code. The DEF level was indeed low.

Case #3: Mercedes

Vehicle Information: 2015 Mercedes-Benz Sprinter 3.0L

Issue + Repair History: P203F code and excessive smoke from exhaust. Recently replaced the DEF tank.

Suggestions to Fix Issue:

• Verify the installation of the DEF tank and sensor.
• Check for any electrical issues in the sensor circuit.
• Inspect for any damage to the wiring harness.

Final Fix: The issue was fixed by replacing a damaged connector in the reductant level sensor wiring harness.

Case #4: Chevrolet

Vehicle Information: 2017 Chevrolet Silverado 2500 HD 6.6L

Issue + Repair History: CEL illuminated with a P203F code. No prior issues with the exhaust system.

Suggestions to Fix Issue:

• Inspect the DEF level and quality.
• Test the reductant level sensor for proper operation.
• Check for any software updates related to the ECM and DEF system.

Final Fix: The technician found the reductant level sensor to be faulty and replaced it, which resolved the P203F code.

Case #5: Ram

Vehicle Information: 2019 Ram 3500 6.7L

Issue + Repair History: P203F code appeared after a long trip. The truck had a recent service including DEF top-up.

Suggestions to Fix Issue:

• Recheck the DEF level in the tank.
• Inspect for any leaks in the DEF system.
• Evaluate the reductant level sensor’s functionality.

Final Fix: It turned out to be a false code due to a temporary sensor glitch. Clearing the code and performing a test drive resolved the issue.

Step	Action
Check DEF Level:	Inspect the Diesel Exhaust Fluid (DEF) level in the storage tank.
Inspect Sensor:	Examine the reductant level sensor for defects or damage.
Verify Fluid Type:	Ensure the correct fluid is in the DEF storage tank.
Electrical Inspection:	Look for any electrical shorts or issues in the sensor circuit.
Sensor Connector Check:	Ensure the sensor connector is secure and free of corrosion.
Wiring Harness Inspection:	Check the wiring harness for damage or chafing.
Sensor Functionality Test:	If possible, test the sensor electronically using a scan tool.
Clear and Retest:	After any repairs, clear the code and perform a test drive to see if the code reappears.