Case IH F-91-31 - ECU – Engine Control Unit (ECU): ECU internal failure - Accelerator pedal position sensor

The control module has detected an internal processing error, memory fault, or plausibility failure specifically tied to the accelerator pedal position sensor circuit. This can be triggered by a severe short in the sensor circuit or an actual hardware failure inside the module itself.

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1. 1

   Voltage Check: Verify that the battery voltage is within the normal operating range (typically 10V to 16V).

2. 2

   Check for Accompanying Codes: Look for other active fault codes related to the accelerator pedal (e.g., codes indicating sensor supply voltage too high/low, such as 2117 or 2186). If a VEXT (external voltage) fault is present, it must be healed first.

3. 3

   Wiring and Connector Inspection: Inspect the wiring harness between the accelerator pedal position sensor and the ECU. Look for chafed wires, water intrusion, or bent pins at the ECU connector.

4. 4

   ECU Reset Test: Clear the fault code using a diagnostic tool, turn the starter switch to the 'OFF' position, wait for the ECU to power down completely, and turn it back 'ON'.

1. 1

   Disconnect Power

   Disconnect the negative battery cable to prevent electrical spikes during the repair.

2. 2

   Isolate the Sensor

   Disconnect the accelerator pedal position sensor harness.

3. 3

   Test the Pedal Sensor

   Using a multimeter, verify the resistance/voltage sweep of the accelerator pedal position sensor. If the sensor is shorted internally, it can drag down the ECU's internal 5V reference circuit. If the sensor fails the sweep test, replace the pedal assembly.

4. 4

   Check ECU Functionality

   Leave the pedal sensor disconnected, reconnect the battery, and turn the key ON. Check the active fault codes. If the 'ECU internal failure' code changes to a standard 'Sensor Circuit Open' code, the ECU is likely fine, and the pedal sensor was the culprit.

5. 5

   ECU Replacement/Reflash

   If the wiring tests good, the sensor is functioning, and the F-91-31 / 3749 code immediately returns upon key-ON, the Engine ECU has suffered a hard internal hardware failure. The ECU must be replaced or reflashed by a certified Case IH dealer.