Fix P205B: Mechanic’s solutions that WORKED

The P205B: Reductant Tank Temperature Sensor Circuit Range/Performance indicates that there is a problem with the reductant tank temperature sensor circuit, which is part of the vehicle’s emissions control system. This sensor helps regulate the temperature of the Diesel Exhaust Fluid (DEF) used in reducing emissions.

P205B quick overview

Meaning	P205B: Reductant Tank Temperature Sensor Circuit Range/Performance
Is it serious?	This code is moderately serious as it can affect the vehicle’s emission control system and may lead to increased emissions
Possible causes	– Faulty reductant tank temperature sensor – Contaminated or incorrect Diesel Exhaust Fluid (DEF) – Wiring or connector issues related to the sensor – Malfunctioning Engine Control Module (ECM)
How to diagnose?	Inspect the Sensor: Check the reductant tank temperature sensor for any visible damage or disconnection. Check DEF Quality: Ensure the DEF fluid is not contaminated and is of the correct type. Examine Wiring and Connectors: Look for any damaged or corroded wiring and connectors associated with the sensor. Test Sensor Functionality: Conduct tests to verify the operation of the sensor. Reset and Clear Codes: After repairs, use a diagnostic scanner to clear the code and monitor if it returns. Consider ECM Update: Check for any software updates for the ECM that might address the issue.

How to fix P205B – learn from mechanics

I looked into P205B 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: Isuzu

Vehicle Information: 2011 Isuzu NPR-HD 5.2L

Issue + Repair History:

• Truck towed in limp mode, driver ignored diesel fluid warning lights for over a year.
• After failing to clear P20C9, the can was baked and the fluid injector was replaced.
• Additional codes appeared during road tests.

Computer Codes & Descriptions:

• P20C9: Reductant Control Module Requested
• P244B: Diesel Particulate Filter Restriction
• P2463: Diesel Particulate Filter Restriction
• P20AD: Reductant Metering Unit Temperature Sensor Performance
• P1490: Refer to Service Manual
• P205B: Reductant Tank Temperature Sensor Circuit

Suggestions to Fix Issue:

• Use a more specific code reader like an Autel for accurate code readings.
• Contact Isuzu for potential emission warranty coverage.
• Utilize IDSS (Isuzu Diagnostic Service System) for proper diagnostics.

Final Fix:

• The issues were mostly covered by dealer warranty.
• The owner received a recall notice for this issue.
• Advised that continued driving exacerbated the problem and that the generic scanner might not provide accurate code descriptions.
• The vehicle was returned to the dealer for resolution.

Case #2: BMW

Vehicle Information: 2011 BMW X5 xDrive35d 3.0L

Issue + Repair History:

• MIL on with a code related to the fuel system.
• Difficulty identifying the location of the temperature sensor in the fuel tank.
• The system includes a passive tank evaluator, fuel level sensor, active tank evaluator, main fuel pump, and transfer pump.

Computer Codes & Descriptions:

• 46F9: Reductant Tank Temperature Sensor Circuit Low
• P205B: Generic Code for Reductant Tank Temperature Sensor Circuit Low

Suggestions to Fix Issue:

• The component in question is part of the active tank of the SCR (Selective Catalytic Reduction) system.
• The active tank, containing the heater and temperature sensor for DEF (Diesel Exhaust Fluid), is located on the right-hand side behind the front bumper panel.
• The active and passive tanks are for DEF fluid, not fuel.
• The reductant tank is a separate unit for DEF fluid.

Final Fix:

• The temperature sensor is inside the tank and available as a unit from the dealer.
• The customer has not yet scheduled an appointment for further inspection.
• Based on information from European technicians, it’s likely an issue with the tank.
• Part number for the active tank: 16197244138. The issue may be covered under emissions warranty.

Case #3: Isuzu

Vehicle Information: 2011 Isuzu Reach 3.0L

Issue + Repair History:

• Vehicle drove in at 5 mph due to empty DEF fluid.
• After filling DEF fluid and clearing DTCs, the vehicle ran fine for 60 miles.
• Encountered DTCs P20C9, P205B, P206, and P208E; replaced redundant tank sending unit and temp sensor.
• After 1 week, vehicle returned in limp mode with DEF system 3/4 full and DTCs P20C9 and P208E present.
• Also encountered transmission codes P0700 and P0707.
• Replaced DEF temp sensor and redundant tank sending unit, and bank 1 NOx sensor.

Computer Codes & Descriptions:

• P20C9: Reductant Injection Valve Stuck Closed Bank 1 Unit 1
• P208E: Reductant Injection Valve Stuck Closed Bank 1
• P0700: Transmission Control System Malfunction
• P0707: Transmission Range Sensor Circuit Low Input
• P205B: Reductant Tank Temperature Sensor Circuit Range/Performance

Suggestions to Fix Issue:

• Utilize factory scan tool to run Adblue system test.
• Check the dosing valve for clogs.
• Use scan tool to reset DEF system counts and actuate the valve.

Final Fix:

• Actuated valves with scan tool; however, same condition and codes returned after 60 miles.
• Decided to replace the DEF injector as no other DTCs have returned.
• The replacement of the DEF injector is expected to resolve the issue.

Case #4: Volkswagen

Vehicle Information: 2014 Volkswagen Passat 2.0L TDI

Issue + Repair History:

• Customer reported Check Engine Light (CEL) on and poor fuel efficiency.
• Scanned and found code P205B: Reductant Tank Temperature Sensor Circuit Range/Performance.
• Checked for visible leaks and damages in the reductant tank and lines; none found.
• Inspected wiring and connectors to the sensor for corrosion or damage; minor corrosion found.

Computer Codes & Descriptions:

• P205B: Reductant Tank Temperature Sensor Circuit Range/Performance

Suggestions to Fix Issue:

• Clean and repair corroded connectors to the reductant tank temperature sensor.
• Test the reductant tank temperature sensor for proper functionality.
• Check for software updates for the Engine Control Module (ECM) related to the reductant system.
• Consider replacing the reductant tank temperature sensor if cleaning connectors does not resolve the issue.

Final Fix:

• After cleaning the connectors and resetting the code, the issue persisted.
• Replaced the reductant tank temperature sensor.
• Post-repair, the vehicle was test-driven, and the CEL did not return.

Case #5: Chevrolet

Vehicle Information: 2012 Chevrolet Cruze 1.8L

Issue + Repair History:

• CEL on with no noticeable change in vehicle performance.
• Diagnostic scan revealed code P205B: Reductant Tank Temperature Sensor Circuit Range/Performance.
• Performed a visual inspection of the DEF system; no leaks or physical damage were observed.
• Noticed DEF fluid discoloration, suggesting contamination.

Computer Codes & Descriptions:

• P205B: Reductant Tank Temperature Sensor Circuit Range/Performance

Suggestions to Fix Issue:

• Drain and replace contaminated DEF fluid.
• Inspect and clean reductant tank temperature sensor and associated wiring.
• Conduct an output test on the reductant tank temperature sensor to ensure it operates within specifications.
• If sensor output is abnormal, recommend sensor replacement.

Final Fix:

• DEF fluid was drained and replaced due to contamination.
• The reductant tank temperature sensor was cleaned, and the wiring was checked; no faults found.
• Sensor output test indicated the sensor was operating correctly.
• After replacing the DEF fluid and clearing the code, the CEL did not reappear during extended test driving.

Common Advice	Brief Description of Diagnostic Step
Inspect Reductant Tank Temperature Sensor	Check the sensor for damage, corrosion, or disconnection.
Check Wiring and Connectors	Examine wiring and connectors to the sensor for signs of wear or corrosion.
Test Sensor Functionality	Perform tests to ensure the sensor is operating within its specified range.
Replace Reductant Tank Temperature Sensor if Necessary	If the sensor is found to be faulty, replace it.
Inspect Reductant (DEF) Fluid	Check the DEF fluid for contamination or discoloration, and replace if necessary.
Reset and Clear Codes After Repairs	Use a diagnostic scanner to clear the code and monitor if it returns after repairs.
Consider ECM Software Updates	Check for any software updates for the vehicle’s Engine Control Module.
Conduct Extended Test Drive	After repairs, perform an extended test drive to ensure the issue is resolved.