Case IH 3712 – ECU / EDC or ECM: Lambda sensor: SCG error of the LSU Heater Power stage (CNH/FPT) / Engine power derate due to DPF regeneration (Cummins)

Code 3712 indicates either a short to ground in the heating circuit of the exhaust oxygen (Lambda) sensor on CNH/FPT engines, or an engine power derate due to high soot accumulation in the DPF requiring regeneration on Cummins engines.

• skid steer
• Farmall 75C
• Farmall 85C
• Farmall 105C
• Farmall 115U
• Maxxum
• Puma
• Quantum
• Patriot 4420
• Steiger
• Magnum

1. 1

   (CNH/FPT Engines) Inspect the wiring harness connecting the Lambda (O2) sensor to the ECU for any chafing, melting, or exposed wires causing a short to ground.

2. 2

   (CNH/FPT Engines) Disconnect the Lambda sensor and inspect the connector pins (typically a 6-pin connector with 5 wires) for moisture, corrosion, or damage.

3. 3

   (CNH/FPT Engines) Test the resistance of the Lambda sensor's internal heater circuit using a multimeter to determine if the short is internal to the sensor.

4. 4

   (CNH/FPT Engines) Check the battery voltage at the sensor to ensure the power stage is receiving proper voltage.

5. 5

   (Cummins Engines) Connect a heavy-duty diagnostic tool (such as Jaltest or Cummins INSITE) to read the exact soot accumulation levels in the DPF.

6. 6

   (Cummins Engines) Check for secondary active fault codes related to the DPF differential pressure sensors, Exhaust Gas Recirculation (EGR) valve, or DEF fluid levels, as these often cause the filter to plug prematurely.

7. 7

   (Cummins Engines) Inspect the DPF housing and differential pressure sensor tubes for physical damage or blockages.

1. 1

   Disconnect battery

   (CNH/FPT Engines) Disconnect the battery to prevent electrical spikes.

2. 2

   Repair or replace wiring harness

   (CNH/FPT Engines) If the wiring harness is damaged, repair the broken/shorted wires and apply heat-shrink tubing, or replace the harness section.

3. 3

   Remove Lambda sensor

   (CNH/FPT Engines) If the wiring is intact but the sensor's internal heater is shorted, unscrew the Lambda sensor from the exhaust stream (M18 x 1.5 thread).

4. 4

   Install new Lambda sensor

   (CNH/FPT Engines) Install the new Lambda sensor and torque to manufacturer specifications.

5. 5

   Reconnect harness

   (CNH/FPT Engines) Reconnect the 6-pin sensor harness.

6. 6

   Clear codes and test

   (CNH/FPT Engines) Reconnect the battery, clear the fault codes using a diagnostic tool, and run the engine to verify the code does not return.

7. 7

   Park machine safely

   (Cummins Engines) Ensure the machine is parked outside in a safe, well-ventilated area away from combustible materials, as exhaust temperatures will become extremely high.

8. 8

   Top off DEF

   (Cummins Engines) Top off the DEF (Diesel Exhaust Fluid) tank if levels are low.

9. 9

   Initiate forced regeneration

   (Cummins Engines) Using your diagnostic software, initiate a forced stationary DPF regeneration.

10. 10

    Run engine at high RPMs

    (Cummins Engines) Allow the engine to run at high RPMs for approximately 40 minutes. The rise in exhaust gas temperature will burn away the built-up soot.

11. 11

    Re-check soot levels

    (Cummins Engines) Once the cycle completes, re-check the soot levels. If the levels are normal, clear the code.

12. 12

    Clean or replace DPF

    (Cummins Engines) If the forced regeneration fails or the filter is irreversibly clogged (ash loaded), the DPF must be physically removed and either sent to a facility for professional baking/cleaning or replaced with a new unit.