Case IH 19158 (DTC 734E) - ECU – Engine Control Unit (ECU): Replacement of the DEF/AdBlue quality sensor - Short to internal ground (reported via CAN structure ComRx_CRI1)

A hard electrical failure within the DEF (Diesel Exhaust Fluid) quality sensor. The sensor has suffered an internal short circuit to ground, preventing it from communicating valid data to the CAN bus network, triggering the code and likely forcing the machine into an emissions derate.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Steiger
• Magnum
• Maxxum
• Farmall (110A, 90C)
• T7 Series
• SV340B
• TR340 Compact Track Loaders

1. 1

   Check for underlying low battery voltage codes (such as SPN 168, FMI 1) which can cause spurious sensor faults.

2. 2

   Inspect the wiring harness leading to the DEF header unit for chafing, melting, or physical damage causing a short to ground.

3. 3

   Disconnect the DEF quality sensor and check the connector for corrosion, moisture, or DEF crystallization bridging the pins.

4. 4

   Isolate the sensor: if the wiring harness and connector test fine, the internal short is confirmed and the sensor is condemned.

1. 1

   Prep the Area

   Turn off the machine, disconnect the battery, and thoroughly clean the top of the DEF tank around the sending unit to prevent dirt from falling into the tank.

2. 2

   Drain the Tank (Optional but Recommended)

   If you suspect contaminated DEF contributed to the sensor failure, drain the tank completely.

3. 3

   Disconnect Lines

   Carefully disconnect the electrical connector and the DEF fluid supply/return lines from the top of the DEF header unit.

4. 4

   Remove the Sensor Assembly

   Unscrew the mounting flange or lock ring securing the DEF header unit to the tank. Carefully pull the entire header unit (which contains the quality sensor, level sensor, and temperature pickup tube) out of the tank.

5. 5

   Install the New Unit

   Insert the replacement DEF header unit, ensuring the O-ring/gasket is properly seated to prevent leaks. Tighten the lock ring.

6. 6

   Reconnect

   Reattach the DEF fluid lines and the electrical connector.

7. 7

   Refill and Clear Codes

   Refill the tank with fresh, high-quality DEF. Reconnect the battery, turn the key on, and use a Case IH Electronic Service Tool (EST) to clear code 19158 (DTC 734E) and run an SCR system self-test.