C18 Marine Auxiliary and Marine Generator Set Engines Caterpillar

Sensor Signal (Analog, Passive) - Test

Usage:

C18 DTP

Use this procedure to troubleshoot the electrical system if a problem is suspected with the sensor or if any one of the diagnostic codes in Table 1 is active or easily repeated.

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Table 1
Diagnostic Codes Table
Code and Description	Conditions which Generate this Code	System Response
110-3 Engine Coolant Temperature Sensor voltage above normal	The engine Electronic Control Module (ECM) detects signal voltage that is more than 4.95 VDC for 8 seconds. The ECM has been powered for at least 2 seconds.	The code is logged if the engine has been running for more than 7 minutes. The ECM uses the last valid engine coolant temperature. If the diagnostic code is active at start-up the ECM will use intake manifold temperature. If intake manifold air temperature is not valid, the ECM will default to 90 °C (194 °F) for engine coolant temperature. The ECM will activate the cooling fan after this code has been active for more than 8 seconds.
110-4 Engine Coolant Temperature Sensor voltage below normal	The ECM detects signal voltage that is less than 0.2 VDC for 8 seconds. The ECM has been powered for at least 2 seconds.
172-3 Intake Manifold Air Temperature Sensor voltage above normal	The engine ECM detects signal voltage that is more than 4.95 VDC for 8 seconds. The ECM has been powered for at least 2 seconds.	The ECM will log the diagnostic code. The ECM will flag the intake manifold air temperature as invalid data and the intake manifold air temperature is set to a default value of 70 °C (158 °F).
172-4 Intake Manifold Air Temperature Sensor voltage below normal	The ECM detects signal voltage that is less than 0.2 VDC for 8 seconds. The ECM has been powered for at least 2 seconds.
174-3 Fuel Temperature Sensor voltage above normal	The engine Electronic Control Module (ECM) detects signal voltage that is more than 4.95 VDC for 8 seconds. The ECM has been powered for at least 2 seconds.	The code is logged. The ECM will flag the fuel temperature as invalid data and the fuel temperature is set to a default value of 40 °C (104 °F).
174-4 Fuel Temperature Sensor voltage below normal	The ECM detects signal voltage that is less than 0.2 VDC for 2 seconds. The ECM has been powered for at least 2 seconds.

System Operation

Use this procedure to troubleshoot any suspect problems with the following sensors:

Coolant temperature sensor
Intake manifold air temperature sensor
Fuel temperature sensor

The sensor signal for the passive sensor is routed from the ECM to terminal 1 of each sensor connector. The sensor return for the passive sensors is routed from the ECM to terminal 2 of each sensor connector.

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Illustration 1	g01365935
Schematic for the passive analog sensors

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Illustration 2	g06112437
Locations of the components for the passive analog sensors (typical left side engine view) (1) Fuel temperature sensor (2) Intake manifold air temperature sensor (3) J2/P2 ECM connectors

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Illustration 3	g06122633
Locations of the components for the passive analog sensors (typical top engine view) (4) Engine coolant temperature sensor

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Illustration 4	g06122641
Locations of the components for the passive analog sensors (typical front engine view) (5) Engine oil temperature sensor

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Illustration 5	g01250277
Terminal locations at the P2 ECM connector for the passive analog sensors (P2-13) Engine coolant temperature (P2-30) Analog sensor return (P2-56) Intake manifold air temperature (P2-62) Fuel temperature

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Illustration 6	g01155187
Terminal locations at the connector for the passive analog sensors (Terminal 1) Sensor signal (Terminal 2) Analog sensor return

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Table 2
Troubleshooting Test Step	Values	Results
1. Check for "Active" or "Logged Diagnostic Codes" A. Remove electrical power from the ECM. B. Connect Caterpillar Electronic Technician (ET) to the service tool connector. C. Restore electrical power to the ECM. D. Monitor the diagnostic codes on Cat ET. Check and record any diagnostic codes. NOTE: Wait at least 30 seconds in order for the diagnostic codes to become active. E. Determine if a diagnostic code has occurred several times. NOTE: A diagnostic code that is logged several times is an indication of an intermittent problem. Most intermittent problems are the result of a poor connection between a socket and a pin in a connector or of a poor connection between a wire and a terminal. F. Determine if the problem is active and related to one of the following diagnostic codes:3,4 G. Remove electrical power from the ECM.	A diagnostic code is not active.	Result: A diagnostic code is not active. The problem may be intermittent. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect". Result: An active 3 diagnostic code is present. Proceed to Test Step 2. Result: An active 4 diagnostic code is present. Proceed to Test Step 4.
2. Check for Battery Voltage on the Signal Wire A. Restore electrical power to the ECM. B. Measure the voltage on the harness side of the sensor connector between pin 1 and engine ground for the suspect sensor. C. Remove electrical power from the ECM.	The signal voltage is less than battery voltage.	Result: The signal voltage is less than battery voltage. Proceed to Test Step 3. Result: The signal voltage is equal to battery voltage. There is a short circuit to battery voltage in the harness. Repair the wiring harness or replace the wiring harness. Verify that the repair has resolved the original problem.
3. Create a Short Circuit at the Connector for the Suspect Sensor A. Disconnect the suspect sensor. B. Fabricate a jumper wire that is long enough to create a test circuit across the harness side of the sensor connector. Crimp connector pins to each end of the jumper wire. C. Install the jumper wire between terminal 1 (sensor signal) and terminal 2 (sensor return) at the sensor connector. D. Restore electrical power to the ECM. E. Access the "Active Diagnostic Code" screen on Cat ET. Check for an active 4 diagnostic code for the suspect sensor. NOTE: Wait at least 30 seconds in order for the diagnostic codes to become active. F. Remove electrical power from the ECM.	A 4 diagnostic code is now active for the suspect sensor.	Result: A 3 diagnostic code was active before creating the short at the sensor connector. A 4 diagnostic code became active after creating the short at the sensor connector. The wiring between the ECM and the sensor connector is OK. Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes. Result: A 3 diagnostic code is still active for the suspect sensor. There is an open circuit between the sensor connector and the ECM. Leave the sensor disconnected. Proceed to Test Step 4.
4. Create an Open Circuit at the Connector for the Suspect Sensor A. Remove electrical power from the ECM. B. Disconnect the sensor connector for the suspect sensor with the active 4 diagnostic code. C. Restore electrical power to the ECM. D. Access the "Active Diagnostic Code" screen on Cat ET. Check for an active 3 diagnostic code. NOTE: Wait at least 30 seconds in order for the diagnostic codes to become active. E. Remove electrical power from the ECM.	A 3 diagnostic code is now active for the suspect sensor.	Result: A 4 diagnostic code was active before disconnecting the sensor. A 3 diagnostic code became active after disconnecting the sensor. The wiring between the ECM and the sensor connector is OK Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes. Result: A 4 diagnostic code is still active for the suspect sensor. There is a short circuit between the sensor connector and the ECM. Proceed to Test Step 5.
5. Check for Proper Operation of the ECM A. Ensure that electrical power has been removed from the ECM. B. Disconnect the J2/P2 ECM connectors. C. Check the operation of the ECM by creating an open at the ECM. a. Remove the signal wire for the suspect sensor from the P2 ECM connector. Refer to Illustration 1 for the correct terminal locations. b. Fabricate a jumper wire that is long enough to create a test circuit between the ECM connector and the negative battery connection. Crimp a connector socket to one end of the jumper wire. c. Install the socket end of the jumper wire into the J2 terminal location that is for the signal wire of the suspect sensor. Hold the loose end of the jumper wire away from any ground source in order to create an open circuit condition. d. Reconnect the J2/P2 ECM connectors. e. Restore electrical power to the ECM. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 30 seconds for activation of the code. An open circuit diagnostic code 3 should be active for the suspect sensor. D. Check the operation of the ECM by creating a short at the ECM. a. Install the loose end of the jumper wire that is for the signal wire for the suspect sensor to negative battery. b. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 30 seconds for activation of the code. A 4 diagnostic code should be active when the wire jumper is installed. c. Remove the jumper wire. Restore the wiring to the original configuration.	A 3 diagnostic code is active while an open circuit condition is present on the signal wire for the suspect sensor. A 4 diagnostic code is active while the signal wire for the suspect sensor is connected to the negative battery connection.	Result: OK The ECM is operating properly. The problem is in the wiring between the ECM and the connector for the sensor. If the code is active for more than one sensor, the problem is most likely in the return wire for the sensors. Repair the return wire for the sensor or replace the harness. If the code is only active for one sensor, the problem is most likely in the signal wire for the sensor. Repair the signal wire for the sensor. Result: The 3 diagnostic code is not active when the open circuit condition is present on the signal wire of the suspect sensor. The ECM is not operating properly. Replace the ECM. Refer to Troubleshooting, "ECM - Replace". Verify that the problem is resolved.