Case IH 3724 – Engine Control Unit (ECU): Lambda sensor: short to battery at IA, IP, UN, VG

The Engine Control Unit has detected a short circuit to battery voltage on the Lambda (Oxygen/O2) sensor's wiring circuits. The specific pins/circuits affected are identified as IA (Pump Current), IP, UN, and VG (Virtual Ground).

• Farmall
• Farmall 115U Pro EP
• Farmall 85A
• Farmall 95A
• Farmall 105A
• Farmall 115A
• Puma 210
• Steiger
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• TR270

1. 1

   Inspect the wiring harness running from the Lambda sensor on the exhaust system to the Engine ECU for chafed, melted, or pinched wires that could be shorting to a 12V power source.

2. 2

   Disconnect the Lambda sensor and inspect both sides of the connector for water ingress, corrosion, or bent pins that could bridge the circuits.

3. 3

   With the sensor disconnected and the key ON, use a multimeter to check the IA, IP, UN, and VG pins on the harness side for voltage. If battery voltage is present, the harness is shorted.

4. 4

   If the harness tests good (no voltage on the signal/ground lines), verify if the short to battery is internal to the Lambda sensor itself.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Harness Repair (If Applicable)

   If a short was found in the wiring harness during diagnostics, repair the damaged section of the wire or replace the engine harness.

3. 3

   Access the Sensor

   Locate the Lambda sensor on the exhaust gas treatment system. You may need to loosen or remove the system heat shield and bonnet supports for access.

4. 4

   Remove the Sensor

   Disconnect the sensor's electrical connector. Carefully unscrew the faulty Lambda sensor from the exhaust pipe.

5. 5

   Install the New Sensor

   Apply a small amount of anti-seize to the threads (if not pre-applied) and install the new Lambda sensor. Tighten to OEM torque specifications.

6. 6

   Reassembly

   Reconnect the electrical connector, reinstall the heat shields, and reconnect the battery.

7. 7

   Clear Codes

   Connect the Electronic Service Tool (EST) to the machine's diagnostic port and clear the inactive 3724 fault code. Run the engine to verify the code does not return.