Case IH 3285 – Engine Control Unit (ECU) / Engine Controller: Engine Regulated 5 Volt Sensor Supply # 3 - Too High. (K = 94 Connector - Vehicle Side, A = 60pin Connector - Engine; A29; K17; K18)

The Engine Control Unit (ECU) provides a regulated 5-volt reference signal to power various engine sensors. Fault code 3285 indicates that the voltage on the #3 5-volt supply circuit is reading higher than the expected 5 volts (typically indicating a short to a high voltage source, such as the 12V battery circuit).

• Farmall
• skid steer
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• Magnum 235 - 340 (Series 4)
• Steiger series tractors

1. 1

   Turn the key switch OFF before disconnecting any modules.

2. 2

   Locate the Engine ECU and inspect the K connector (94-pin, Vehicle Side) and the A connector (60-pin, Engine Side), specifically checking pins A29, K17, and K18.

3. 3

   Verify that the connectors to the ECU are not damaged, are properly connected, and connector locks are not broken.

4. 4

   Check the wiring harness along the 5-volt supply #3 circuit for chafing, melted insulation, or pinched wires that could cause a short to a 12V power source.

5. 5

   Disconnect the sensors powered by the #3 5-volt supply one at a time to see if the voltage returns to normal (5V), indicating an internally shorted sensor.

1. 1

   Power Down

   Turn the machine off and disconnect the negative battery terminal to prevent electrical spikes.

2. 2

   Isolate the Short

   Based on the diagnostic checks, trace the wiring harness from ECU pins A29, K17, and K18 to their respective sensors.

3. 3

   Repair Wiring

   If damaged wiring is found (e.g., a wire shorting to a 12V source), splice and repair the damaged section using OEM-approved heat-shrink connectors, or replace that section of the harness.

4. 4

   Replace Faulty Sensor

   If the diagnostic isolation test proved a sensor was internally shorting the 5V reference circuit to a higher voltage, replace the affected sensor.

5. 5

   ECU Replacement (Worst Case)

   If the wiring harness tests perfectly (no shorts to power) and all sensors are functioning, the Engine Controller itself may have suffered an internal hardware failure on the 5V driver. In this case, the Engine Controller must be replaced.

6. 6

   Clear Codes and Retest

   Reconnect the battery, turn the key switch ON, and use the Electronic Service Tool (EST) to clear the inactive fault codes. Run the engine to verify the code does not return.