Case IH F-729-03 - ECU – Engine ECU: Intake air heater actuator is shorted to battery voltage

The Engine Control Unit (ECU) has detected a short circuit to the battery voltage on the circuit responsible for controlling the intake air heater actuator (typically a relay or solenoid).

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1. 1

   Check for active co-existing faults, specifically code 3905 (F-729-06) – Intake air heater ECU driver overtemperature error. Resolve this first if active.

2. 2

   Inspect the coil of the intake air heater relay (K-relay) for internal shorting.

3. 3

   Inspect the wiring harness between the Engine ECU and the intake air heater relay for rubbed, melted, or pinched wires that could cause a short to battery voltage.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical arcing or further damage to the ECU.

2. 2

   Locate the Actuator

   Locate the intake air heater relay/solenoid, which is typically mounted near the engine block or intake manifold.

3. 3

   Disconnect and Isolate

   Disconnect the wiring harness connector from the intake air heater relay.

4. 4

   Test the Wiring

   Using a digital multimeter, test the signal wire coming from the ECU to the relay connector for continuity to battery power. If voltage is present (when it shouldn't be) or continuity to a power wire is found, the wiring harness has a short and must be repaired or replaced.

5. 5

   Test the Relay

   Measure the resistance across the relay coil terminals. If the resistance is out of specification (reading as a dead short), the relay itself has failed internally and is causing the short to battery voltage.

6. 6

   Replace/Repair

   Replace the faulty relay or repair the damaged section of the wiring harness.

7. 7

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic tool to clear the inactive fault codes. Start the engine to verify the code does not return.