Case IH 3154 (F-729-03) – Engine Control Unit (ECU): Intake air heater actuator is shorted to battery voltage

The Engine Control Unit (ECU) monitors the control circuit for the intake air heater relay (designated as K-023 in Case IH schematics). If the ECU detects a short to a high source (battery voltage) on this circuit, it logs this fault. This condition prevents the intake air heater from operating correctly, which can lead to hard starting and excessive white smoke in cold conditions.

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1. 1

   Check if fault code 3905 (F-729-06) 'Intake air heater ECU driver overtemperature error' is also active. If it is, diagnose and clear that fault first.

2. 2

   Test the coil of the intake air heater relay (K-023) for internal shorts.

3. 3

   Visually inspect the relevant wiring harnesses and connectors between the ECU (A-095) and the relay (K-023) for damage, bent or dislocated pins, corroded terminals, or broken wires.

4. 4

   Flex the involved harnesses while monitoring a multimeter to reveal intermittent shorts to battery voltage in the wiring.

5. 5

   If the wiring and relay test fine (no continuity to battery voltage on the ground/control side), check the ECU for the appropriate software version.

1. 1

   Disconnect Power

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

2. 2

   Locate the Relay

   Locate the intake air heater relay (K-023), typically mounted near the engine block, intake manifold, or in the main engine fuse/relay box.

3. 3

   Test and Repair Wiring

   Using a multimeter, trace the control wire from the relay back to the ECU. If a short to battery voltage is found in the harness, open the loom, locate the chafed or melted wire, and repair the conductor using OEM-approved splicing methods.

4. 4

   Replace the Relay

   If the wiring is intact but the relay coil is internally shorted to its power supply, remove the mounting hardware and electrical connections, and install a new intake air heater relay.

5. 5

   Re-flash/Replace ECU

   If the harness and relay are in perfect condition but the ECU continues to output battery voltage on the control circuit constantly, the ECU's internal driver is likely shorted. The ECU (A-095) will need to be re-flashed or replaced by an authorized dealer.

6. 6

   Clear Codes

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