Case IH 3708 – Engine Control Unit (ECU) / EDC: Lambda sensor: open circuit at the lambda sensor pump current pin - IP (lambda = 1 detection)

The engine's control system has detected a break in the electrical continuity (an open circuit) specifically on the pump current circuit of the exhaust lambda (oxygen) sensor. The lambda sensor relies on this pump current to measure the oxygen content in the exhaust gases accurately; without it, the sensor cannot function, and emissions monitoring is compromised.

• Farmall
• Farmall 115U Pro EP
• Farmall 60A
• Farmall 70A
• Puma 210
• Steiger
• Case 21F
• Case 121F
• Case 221F
• Case 321F
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Visually inspect the lambda sensor on the exhaust system and the wiring harness leading to it for chafed, melted, or broken wires.

2. 2

   Disconnect the lambda sensor's electrical connector (5-wire oval plug with 6 pins) and inspect both sides for corrosion, moisture, or pins that have been pushed back out of their seating.

3. 3

   Using a multimeter, test the wiring harness from the sensor connector back to the Engine ECU for continuity. Infinite resistance on the pump current pin wire indicates a broken harness. If the harness tests good, the open circuit is internal to the lambda sensor itself.

1. 1

   Turn off the machine's ignition and disconnect the negative battery cable.

2. 2

   If the diagnostic tests revealed a broken wire in the harness, repair the wiring or replace the affected harness section.

3. 3

   If the wiring is intact, the lambda sensor has failed internally and must be replaced. Disconnect the sensor's electrical connector.

4. 4

   Using a specialized oxygen sensor socket, carefully unscrew the faulty lambda sensor from the exhaust pipe.

5. 5

   Apply a light coat of anti-seize compound to the threads of the new sensor (if it does not come pre-coated).

   Be careful not to get any compound on the sensor tip.

6. 6

   Thread the new lambda sensor into the exhaust and tighten it to the manufacturer's specified torque.

7. 7

   Reconnect the electrical connector, ensuring it clicks securely into place.

8. 8

   Reconnect the battery, start the engine, and use a diagnostic service tool to clear the inactive 3708 fault code from the ECU.