Case IH 3712 – Engine: Lambda sensor: SCG error of the LSU Heater Power stage

The control module has detected that the voltage on the electrical circuit powering the Lambda sensor's internal heater is being pulled to ground (Short Circuit to Ground). This is typically caused by a damaged wiring harness or an internal short circuit within the sensor itself.

• Farmall
• Farmall 115U Pro EP
• Farmall 100C
• Puma
• Maxxum
• Skid Steer Loaders
• SR175
• Compact Track Loaders

1. 1

   Turn the ignition switch to the OFF position and visually inspect the engine wiring harness between the Lambda sensor and the Engine ECU for melted insulation, chafing, or pinched wires that could cause a short to ground.

2. 2

   Disconnect the sensor and use a high-impedance digital volt/ohm meter (DMM) to measure the resistance of the wiring harness pins to ground and to the ECU. Do not use a normal analogue multimeter as it can burn out the sensor or give false readings.

3. 3

   Verify that the ECU software is at the most current status, as software updates can sometimes resolve erroneous heater circuit logic.

1. 1

   Power Down

   Turn off the machine and allow the exhaust system to cool completely to prevent burns.

2. 2

   Repair Wiring

   If diagnostic tests revealed a short to ground in the engine harness (e.g., resistance to ground is found on the power supply wire), locate the damaged section, repair the wiring, and secure it away from exhaust heat.

3. 3

   Replace the Sensor

   If the harness tests good, the short is internal to the Lambda sensor's heater element. Disconnect the electrical connector, use an oxygen sensor socket to unthread the faulty sensor, apply anti-seize to the new sensor threads, install it into the exhaust, and reconnect the electrical connector.

4. 4

   Re-flash / Reset the ECU

   Re-flash the control module using a dealer diagnostic tool (like the CNH EST) to allow for the new sensor adjustments to be learned.

5. 5

   Clear Codes

   Clear the inactive 3712 fault code and run the engine to verify the repair.