C8.7 and C12.9 Marine Engines Caterpillar

Air Inlet Heater Circuit - Test

Usage:

C8.7 CS7

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Table 1
J1939 Code and Description	Comments
729-3 Engine Intake Air Heater Driver #1: Voltage Above Normal	The ECM has detected a short circuit to a positive voltage on the circuit for the intake air heater relay.
729-4 Engine Intake Air Heater Driver #1: Voltage Below Normal	The ECM has detected a short to ground on the circuit for the intake air heater relay.
729-5 Engine Intake Air Heater Driver #1: Current Above Normal	The ECM has detected an open on the circuit for the intake air heater relay.
729-12 Engine Intake Air Heater Driver #1: Failure	The ECM has detected an over temperature condition on the output for the intake air heater relay.

Inlet Air Heater

This feature is used to improve the cold start capability of the engine and to reduce white smoke. The ECM controls the Air Inlet Heater Grid through the Air Inlet Heater Relay.

The Air Inlet Heater operation is determined at three different times; Power Up/Preheat, Cranking, and Engine Started Cycle, based on various engine parameters.

A wait to start lamp is present to warn the operator the engine is cold and needs to wait until the Inlet Air Heater have heated to the correct level before cranking.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Check for Codes A. Turn the keyswitch to the ON position. B. Connect the electronic service tool to the diagnostic connector. C. Make a note of any active diagnostic codes.	Codes	Result: Diagnostic code 729-3 is active or logged. Proceed to Test Step 2. Result:Diagnostic code 729-4 is active. Proceed to Test Step 3. Result:A 729-5 diagnostic code is active or logged. Proceed to test Step 4. Result: A 729-12 diagnostic code is active or logged. Proceed to Test Step 5.
2. Check for a Short to Battery Positive or Short to Ground A. Turn the keyswitch to the OFF position. B. Unplug the connector for the starter motor relay. C. Turn the keyswitch to the ON position. D. Use the Cat^® Electronic Technician (ET) override to energize the circuit for the air inlet heater relay. E. Observe status of active diagnostic code 729-3.	Codes	Result: Diagnostic code 729-3 remains active. Repair: There is a short to a positive voltage in between the engine ECM and the connector for the air inlet heater relay. Repair or replace the wiring harness. Result:Diagnostic code 729-3 is no longer active and is now logged. Repair: The air inlet heater relay was shorted to a positive power source. Replace the air inlet heater relay.
3. Check for a Short to Ground A. Turn the keyswitch to the OFF position. B. Unplug the connector for the air inlet heater relay. C. Turn the keyswitch to the ON position. D. Use the Cat ET override to energize the circuit for the air inlet heater relay. E. Observe status of diagnostic 729-4.	Codes	Result: Diagnostic code 729-4 is no longer active is now logged. A 729-5 diagnostic code is active. Result: Diagnostic code 729-4 is no longer active is now logged. A 729-5 diagnostic code is active. Result: Diagnostic code 729-4 remained active. There is a short to ground in between the connector for the air inlet heater relay and the ECM. Repair: Repair or replace the wiring harness.
4. Check for an Open Circuit A. Turn the keyswitch to the OFF position. B. Disconnect the connector for the air inlet heater relay. C. Install a jumper wire to create a short circuit between terminals 1 and 2 on the connector for the air inlet heater relay. D. Turn the keyswitch to the ON position. E. Use the Cat ET override to energize the circuit for the inlet air heater. F. Observe the status of the 729-5 diagnostic code.	Codes	Result: Diagnostic code 729-5 is now logged and 729-4 is now active. Repair: Replace the air inlet heater relay. Result: Diagnostic code 729-5 remains active with the jumper wire in place. Repair: There is an open circuit in between the connector for the air inlet heater relay and the engine ECM. Repair or replace the wiring harness.
5. Test ECM Output A. Turn the keyswitch to the OFF position. B. Disconnect the air inlet heater relay connector. C. Turn the keyswitch to the ON position. D. Connect to Cat ET. E. Navigate in Cat ET to "diagnostic tests", "override parameter", and select "grid heater relay" override. F. Observe diagnostic codes.	Codes	Result: Diagnostic code 729-12 is active with the connector removed from the ECM. The relay and the override are ON. Repair: The ECM has failed. Replace the Engine ECM. Before replacing the ECM, if possible, contact the Dealer Solution Network. Result: Diagnostic code 729-12 did not become active with the J1/P1 connector removed. The air inlet heater relay may be shorted. Replace the air inlet heater relay. If nothing found, contact the DSN.

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).