The DEF (Diesel Exhaust Fluid) system in your diesel vehicle is crucial for emissions control. However, a faulty DEF tank temperature sensor can trigger warning lights and even limit engine performance. This guide provides a detailed walkthrough of replacing the Def Tank Temp Sensor, often referred to as the “DEF tank temp sensor hack.”
This modification involves replacing the existing sensor with a thermistor, effectively bypassing the faulty component. While this guide provides comprehensive instructions, it’s crucial to understand that modifying your vehicle’s emissions system could have legal implications depending on your local regulations.
Understanding the DEF System and the Temperature Sensor
The DEF system injects a urea-based solution into the exhaust stream to reduce harmful nitrogen oxide emissions. The temperature sensor plays a vital role by ensuring the DEF is at the optimal temperature for efficient operation. A malfunctioning sensor can lead to inaccurate readings, causing the system to malfunction.
Replacing the DEF Tank Temp Sensor: Step-by-Step Instructions
The process of replacing the DEF tank temp sensor can be broken down into several key steps:
Accessing the DEF Tank
- Prepare the Vehicle: Securely lift the rear of the vehicle using ramps or jack stands. Disconnect the negative battery terminal.
- Lower the Exhaust: Remove the nuts securing the exhaust system mounts to the differential housing (likely 19mm) and near the front of the urea tank (likely 13mm). Carefully slide the rubber hangers off the mounting rods at the exhaust tips and lower the exhaust system.
- Remove Heat Shields: Using a 10mm wrench/socket, remove the nuts securing the heat shields between the mufflers and the DEF tank. An 8mm socket will remove perimeter screws. Gently lower the heat shields.
- Detach the DEF Tank: Remove the two nuts (likely 19mm) holding the DEF tank to the trunk floor, located above the mufflers. Also, remove the 10mm plastic nut fastening the battery cable tray to the trunk floor pan near the battery.
- Remove Trunk Floor: Remove the ten 10mm nuts securing the trunk floor pan and remove the plastic fascia protecting the trunk latch and taillights. This may involve prying out plastic rivets and removing screws under oval caps. Carefully lift the trunk floor to expose the DEF tank.
Replacing the Sensor
- Locate the Connector: Identify the electrical connector on the DEF tank. It typically has four wires: two larger wires for the heater and two smaller wires for the thermistor.
- Splice the New Thermistor: Cut the two smaller wires on the tank side of the connector. Splice the new thermistor to the small wires coming from the connector. Secure the thermistor to the wiring harness or bond it to the tank.
Alternative Method: Internal Replacement (More Involved)
- Remove the Tank Lid: Disconnect all electrical connectors and hoses from the DEF tank lid. Unscrew the large ring nut attaching the lid to the tank. Carefully slide the lid out.
- Replace the Sensor: Fish the new thermistor leads through the existing grommet using lubricated pliers or a small screwdriver. Reassemble the tank components.
Reassembly
Reinstall all components in the reverse order of removal, ensuring all connections are secure and properly aligned.
Conclusion
Replacing the DEF tank temp sensor with a thermistor can be a cost-effective solution to a malfunctioning sensor. However, remember to consult your local regulations regarding modifications to emissions systems. This guide provides a comprehensive overview of the process, but always prioritize safety and consult a qualified mechanic if you have any doubts. Remember to double-check all connections before operating the vehicle.
