C18 Marine Auxiliary and Marine Generator Set Engines Caterpillar

Sensor Signal (Analog, Active) - Test

Usage:

C18 DTP

Use this procedure to troubleshoot the electrical system if a problem is suspected with the sensors 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
94-3 Fuel Delivery Pressure Sensor voltage above normal	The Electronic Control Module (ECM) detects signal voltage that is above normal for 8 seconds.	The code is logged. The value of the parameter is set to a gauge pressure of 600 kPa (87 psi).
94-4 Fuel Delivery Pressure Sensor voltage below normal	The ECM detects signal voltage that is below normal for 8 seconds.
100-3 Engine Oil Pressure Sensor voltage above normal	The ECM detects signal voltage that is above normal for 8 seconds.	The code is logged. The value of the parameter is set to a gauge pressure of 600 kPa (87 psi).
100-4 Engine Oil Pressure Sensor voltage below normal	The ECM detects signal voltage that is below normal for eight second.
100-10 Engine Oil Pressure Sensor abnormal rate of change	The signal voltage has not changed at a normal rate for 30 seconds. Engine speed must be above 600 rpm.
127-3 Transmission Oil Pressure Sensor voltage above normal	The ECM detects signal voltage that is above normal.	The code is logged.
127-4 Transmission Oil Pressure Sensor voltage below normal	The ECM detects signal voltage that is below normal.	The code is logged.
177-3 Transmission Oil Temperature Sensor voltage above normal	The ECM detects signal voltage that is above normal.	The code is logged.
177-4 Transmission Oil Temperature Sensor voltage below normal	The ECM detects signal voltage that is below normal.	The code is logged.
1785-3 Intake Manifold Pressure Sensor voltage above normal	The ECM detects signal voltage that is above normal for 2 seconds.	The code is logged. The value of the parameter is set to a gauge pressure of 100 kPa (15 psi).
1785-4 Intake Manifold Pressure Sensor voltage below normal	The ECM detects signal voltage that is below normal for 2 seconds.
1785-10 Intake Manifold Pressure Sensor abnormal rate of change	The signal voltage has not changed at a normal rate for 30 seconds. Engine speed must be above 1000 rpm.

System Operation

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

Fuel pressure sensor
Engine oil pressure sensor
Transmission oil pressure sensor
Transmission oil temperature sensor
Intake manifold pressure sensor
Coolant level sensor
Exhaust temperature sensor

The supply voltage is routed to terminal A of each sensor connector. The sensor return is routed to terminal B of each sensor connector. The sensor signal is routed to terminal C of each sensor connector. The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.

The ECM performs an automatic calibration of these sensors whenever the ECM is powered and the engine is off for at least 5 seconds. During an automatic calibration, the ECM calibrates pressure sensors to the value of the atmospheric pressure at sea level. This calibration value is then checked against an acceptable offset pressure range.

The ECM continuously outputs a pull-up voltage on the input terminal from an analog sensor. The ECM uses this pull-up voltage in order to detect an open or a short in the signal circuit. When the ECM detects the presence of a voltage that is above the normal range of the sensor on the signal circuit, the ECM will generate an open circuit diagnostic code 3 for that sensor. When the ECM detects the absence of the pull-up voltage on the signal circuit, the ECM will generate a short circuit diagnostic code 4 for that sensor. The presence of pull-up voltage at the sensor connector indicates that the wires from the sensor connector to the ECM are not open or shorted to ground.

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Illustration 1	g01373607
Schematic for the analog sensors

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Illustration 2	g06122581
Locations of the connectors for the analog sensors (typical front side engine view) (1) Coolant level sensor (2) Engine oil pressure sensor

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Illustration 3	g06122728
Locations of the connectors for the analog sensors (typical left side engine view) (3) J2/P2 ECM connectors

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Illustration 4	g01373688
Locations of the connectors for the analog sensors (typical rear engine view) (5) Transmission oil pressure sensor (6) Transmission oil temperature sensor

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Illustration 5	g01373689
Terminal locations at the P2 ECM connector for the analog sensors (P2-15) Intake manifold pressure sensor (P2-16) Transmission oil pressure sensor (P2-17) Analog return (P2-27) Transmission oil temperature sensor (P2-28) Engine oil pressure sensor (P2-40) Fuel pressure sensor (P2-54) Analog return (P2-72) Analog sensor supply (P2-80) Analog sensor supply (P2-81) Digital sensor supply (P2-93) Digital return

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Illustration 6	g01159881
Terminal locations at the sensor connector (Terminal A) Sensor supply (Terminal B) Sensor return (Terminal C) Signal

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Table 2
Troubleshooting Test Step	Expected Result	Results
1. Check for "Active" and "Logged" Diagnostic Codes A. Connect Caterpillar Electronic Technician (ET) to the service tool connector. B. Turn the keyswitch to the ON position. C. 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. D. 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 bad connection between a socket and a pin in a connector or a bad connection between a wire and a terminal. The problem may be caused by moisture, corrosion, or wear. E. Determine if the problem is active and related to one of the following diagnostic codes:	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: "-10" diagnostic code is active A 10 diagnostic code indicates an open in the voltage supply to a sensor. If the code is only present for one sensor, the open will be between the sensor connector and a splice. If the open is for two or more sensors the open will be before the splice for the voltage supply to those sensors. Repair the open in the wiring or connectors. Refer to the electrical schematic for the locations of splices in the harness. Refer to Troubleshooting, "Sensor Supply - Test" for information that is related to troubleshooting the sensor supply. Result: "- 3" code or a "4" code is active. Proceed to Test Step 2.
2. Check the 5 V Supply at the Sensor Connector A. Do not disconnect the suspect connector. B. Connect a multimeter between pin A and pin B on the sensor side of the connector for the suspect sensor. C. Measure the voltage between pin A and pin B for the suspect sensor. D. Wiggle the harness while you monitor the voltage on the voltmeter. Perform the 45 N (10 lb) pull test on each wire in the circuit. Each terminal and each connector should easily withstand this tension and each wire should remain in the connector body.	The supply voltage is approximately 5.0 ± 0.5 VDC.	Result: The supply voltage is approximately 5.0 ± 0.5 VDC. An active 3 diagnostic code is present. Proceed to Test Step 3. Result: The supply voltage is approximately 5.0 ± 0.5 VDC. An active 4 diagnostic code is present. Proceed to Test Step 4. Proceed to Test Step 4.
	The supply voltage is approximately 5.0 ± 0.5 VDC.
3. Check for Battery Voltage on the Signal Wire A. Measure the voltage on the harness side of the sensor connector between pin B and pin C for the suspect sensor.	The signal voltage is less than battery voltage.	Result: The signal voltage is less than battery voltage. Proceed to Test Step 4. Result: The signal voltage is equal to battery voltage. There is a short in the harness to the battery. Repair the wiring.
4. Create a Short Circuit at the Sensor Connector A. Turn the keyswitch to the OFF position. B. Disconnect the suspect sensor. C. Fabricate a wire jumper that is long enough to create a test circuit at the sensor connector. Use the jumper wire to create a short between terminal C (sensor signal) and terminal B (sensor return) at the sensor connector. D. Turn the keyswitch to the ON position. E.Monitor the diagnostic codes 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. Turn the keyswitch to the OFF position.	A 4 diagnostic code is now active for the suspect sensor.	Result: A 3 diagnostic code was active before installing the jumper wire at the sensor connector. A 4 diagnostic code became active after installing the jumper wire at the sensor connector. The harness and the ECM are OK. There may be a problem with the sensor. 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. The problem may be in the harness or with the ECM. Proceed to Test Step 6.
5. Create an Open at the Suspect Sensor Connector A. Turn the keyswitch to the OFF position. B. Disconnect the sensor connector of the suspect sensor with the active 4 diagnostic code. C. Turn the keyswitch to the ON position. D. Monitor the diagnostic codes on Cat ET. Check for an active 3 diagnostic code for the suspect sensor. NOTE: Wait at least 30 seconds in order for the diagnostic codes to become active. E. Turn the keyswitch to the OFF position.	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 harness and the ECM are OK. There may be a problem with the sensor. 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. Leave the sensor disconnected. The problem may be in the harness or with the ECM. Proceed to Test Step 6.
6. Test the Operation of the ECM A. Fabricate a jumper wire that can be used to replace the signal wire in the ECM connector for the suspect sensor. Crimp a connector socket to one end of the jumper wire. B. Disconnect the appropriate ECM connector for the suspect sensor. C. Remove the signal wire for the suspect sensor from the ECM connector. D. Install the jumper wire into the terminal location for the suspect signal wire of the sensor at the ECM connector. E. Connect the ECM connector. F. Check the operation of the ECM by creating an open at the ECM: a. Hold the loose end of the jumper wire away from any components in order to create an open circuit condition. b. Turn the keyswitch to the ON position. c. Monitor the active diagnostic code screen on Cat ET. Check for a 3 diagnostic code for the suspect sensor. NOTE: Wait at least 30 seconds in order for the diagnostic codes to become active. G. Check the operation of the ECM by creating a short circuit at the ECM: a. Short the jumper wire for the suspect sensor to the sensor's return in order to create a short circuit condition. b.Monitor the active diagnostic code screen on Cat ET. Check for a 3 diagnostic code for the suspect sensor. H. Turn the keyswitch to the OFF position. I. Remove all jumper wires. Return the wiring to the original configuration.	A 3 diagnostic code is active when the sensor signal wire is removed from the ECM connector. A 4 diagnostic code is active when the signal wire is shorted to the analog return.	Result: 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 sensor. Repair the analog 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: One of the following conditions exists: The 3 diagnostic code is not active when the sensor signal wire is disconnected. The 4 diagnostic code is not active when the wire jumper is shorted to the analog return. Replace the ECM. Refer to Troubleshooting, "ECM - Replace". Verify that the problem is resolved.