Case IH 3440 – Engine Control Unit (ECU A-095): Auxiliary power relay low side ECU driver circuit over temperature failure

The Engine Control Unit (ECU) actively monitors the K-064 auxiliary power relay low side circuit for an over-temperature or over-current condition. If the circuit exceeds safe thresholds, this fault is logged. On specific Tier 4 emissions equipment, this DTC is mapped to a DEF/AdBlue supply module pump motor ECU driver over temperature failure.

• Steiger T4B
• Puma Series Tractors
• 240 Series Axial-Flow Combines

1. 1

   Verify that the machine's battery has not been connected to an external power supply (like a jump starter or external charger).

2. 2

   Check the ECU A-095 for the appropriate software version to see if a re-flash is necessary.

3. 3

   Test the K-064 auxiliary power relay coil for internal faults or excessive resistance that could cause an over-current draw.

4. 4

   Inspect the wiring harness between the ECU A-095 and the K-064 relay (or DEF pump module) for a short to ground or short to battery condition.

5. 5

   Verify the machine's charging system is not overcharging, which can cause circuit over-temperature conditions.

1. 1

   Isolate Power

   Turn off the machine and disconnect any external power supplies or chargers from the battery. Clear the code and retest. If the code returns, proceed to step 2.

2. 2

   Inspect and Replace the Relay

   Locate the auxiliary power relay (K-064). Test the relay with a multimeter. If the coil is faulty or shorted, replace the relay.

3. 3

   Test the Wiring Harness

   Disconnect the harness at the ECU A-095 and at the K-064 relay. Check for continuity, shorts to ground, and shorts to voltage on the low-side control circuit. Repair or replace the wiring harness if damage or a short is found.

4. 4

   DEF/AdBlue Pump Inspection (240 Series Combines Only)

   If working on a 240 Series Combine, inspect the DEF/AdBlue supply module pump motor. An internal short in the pump motor can cause the ECU driver to overheat. Replace the DEF supply module if it is drawing excessive current.

5. 5

   ECU Re-flash / Replacement

   If the relay, DEF pump (if applicable), and wiring harness are all in good working order, re-flash the ECU A-095 with the latest software. If the fault still persists, the ECU A-095 itself has suffered internal hardware driver damage and must be replaced.