Case IH 187 – Engine Control Module (ECM): Sensor Supply 2 Voltage is too low

The Engine Control Module (ECM) has detected that the 5-volt reference circuit (Sensor Supply Number 2) has dropped below the acceptable voltage threshold. This causes a loss of communication with critical engine sensors, typically resulting in an engine power derate or reduced performance.

• MX Magnum
• STX Steiger
• MX Magnum Series
• TG Series Tractors
• Puma Series
• Magnum 235 - 340 (Series 4)
• Combines (7130, 7240, 8240, 9240)

1. 1

   Perform a sensor isolation test: Turn key ON (engine OFF) and disconnect sensors on the Sensor Supply 2 circuit one at a time (Camshaft Position, Intake Manifold Pressure, Fuel Pressure). If voltage returns to 5V, the unplugged sensor has an internal short.

2. 2

   Inspect the engine wiring harness for chafing, rubbing, or pinched wires that could cause a short to ground.

3. 3

   Disconnect the engine harness from the ECM and inspect the connector pins (specifically the Sensor Supply 2 pin) for moisture, corrosion, or bent pins.

4. 4

   Measure the voltage directly at the Sensor Supply 2 pin on the ECM with the harness disconnected. If it outputs less than 5 volts, the ECM's internal power supply has failed.

1. 1

   Turn off the equipment

   Remove the key to ensure the ECM is powered down before disconnecting any components.

2. 2

   Disconnect the engine harness

   Disconnect from the sensors on the #2 supply circuit to perform the isolation test.

3. 3

   Replace the faulty component

   If a sensor is shorted, replace the specific sensor. If the harness is shorted to ground and cannot be repaired, replace the engine wiring harness. If the ECM is outputting low voltage internally, replace the ECM.

4. 4

   Reconnect all harnesses

   Ensure the connectors click into place securely.

5. 5

   Clear the fault codes

   Use an electronic service tool (like INSITE or the Case IH diagnostic tool).

6. 6

   Test run the engine

   Verify the code does not return and that engine performance is restored.