C7.1 Engines and Generator Sets Caterpillar

Sensor Signal (Analog, Passive) - Test

Usage:

C7.1 770

This procedure covers the following diagnostic codes:

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Table 1
Diagnostic Trouble Codes for Analog Passive Sensors
J1939 Code	CDL Code	Code Description (code descriptions may vary)	Comments
105-3	172-3	Intake Manifold Air Temperature Sensor : Voltage Above Normal	The Electronic Control Module (ECM) detects the following conditions: The signal voltage from the intake manifold air temperature sensor is greater than 4.95 VDC for more than 8 seconds. Engine coolant temperature is above −10 °C (15.0 °F). The ECM will use the default value of 70 °C (158 °F) for the intake manifold air temperature. "Voltage High" will be displayed next to the status for "Intake Manifold Air Temperature" on the electronic service tool. The engine may show the following symptoms: Poor stability Poor cold running Poor acceleration under load White smoke
105-4	172-4	Intake Manifold Air Temperature Sensor : Voltage Below Normal	The ECM detects the following conditions: The signal voltage from the intake manifold air temperature sensor is less than 0.2 VDC for more than 8 seconds. The ECM will use the default value of 70 °C (158°F) for the intake manifold air temperature. "Voltage Low" will be displayed next to the status for "Intake Manifold Air Temperature" on the electronic service tool. The engine may show the following symptoms: Poor stability Poor cold running Poor acceleration under load White smoke
110-3	110-3	Engine Coolant Temperature Sensor : Voltage Above Normal	The ECM detects the following conditions: The signal voltage from the engine coolant temperature sensor is greater than 4.95 VDC for more than 8 seconds. An active diagnostic code will be generated after 8 seconds. The ECM will default to 90 °C (194 °F) for engine coolant temperature. "Voltage Above Normal" will be displayed next to the status for "Engine Coolant Temperature" on the electronic service tool. The engine may show the following symptoms: Poor stability Poor cold running White smoke
110-4	110-4	Engine Coolant Temperature Sensor : Voltage Below Normal	The ECM detects the following conditions: The signal voltage from the engine coolant temperature sensor is less than 0.2 VDC for more than 8 seconds. An active diagnostic code will be generated after 8 seconds. The diagnostic code will be logged if the engine has been operating for more than 7 minutes. The ECM will default to 90 °C (194 °F) for engine coolant temperature. "Voltage Below Normal" will be displayed next to the status for "Engine Coolant Temperature" on the electronic service tool. The engine may show the following symptoms: Poor stability Poor cold running White smoke
172-3	2526-3	Air Inlet Temperature Sensor : Voltage Above Normal	The ECM detects the following conditions: The signal voltage from the air inlet temperature sensor is greater than 4.95 VDC for at least 8 seconds.
172-4	2526-4	Air Inlet Temperature Sensor : Voltage Below Normal	The ECM detects the following conditions: The signal voltage from the air inlet temperature sensor is less than 0.2 VDC for at least 8 seconds.
174-3	174-3	Fuel Temperature Sensor : Voltage Above Normal	The ECM detects the following conditions: The signal voltage from the fuel temperature sensor is greater than 4.95 VDC for more than 8 seconds. The ECM will default to 40° C (104° F) for fuel temperature. "Voltage Above Normal" will be displayed next to the status for "Engine Fuel Temperature" on the electronic service tool.
174-4	174-4	Fuel Temperature Sensor : Voltage Below Normal	The ECM detects the following conditions: The signal voltage from the fuel temperature sensor is less than 0.2 VDC for more than 8 seconds. The ECM will default to 40° C (104° F) for fuel temperature. "Voltage Below Normal" will be displayed next to the status for "Engine Fuel Temperature" on the electronic service tool.
412-3	3386-3	EGR Temperature Sensor : Voltage Above Normal	The ECM detects the following conditions: The signal voltage from the Nox Reduction System (NRS) temperature sensor is greater than 4.975 VDC for more than 8 seconds.
412-4	3386-4	EGR Temperature Sensor : Voltage Below Normal	The ECM detects the following conditions: The signal voltage from the NRS temperature sensor is less than 0.2 VDC for more than 8 seconds.

Note: The following conditions must exist before any of the above codes will become active:

The ECM has been powered for at least 2 seconds.
There are no active 168-X diagnostic codes.

The ECM will log the diagnostic code. If equipped, the warning light will come on.

This procedure covers open circuit diagnostic codes and short circuit diagnostic codes that are associated with the following sensors:

Coolant temperature sensor
Intake manifold air temperature sensor
Fuel temperature sensor
Air inlet temperature sensor
NRS inlet temperature sensor

The following background information is related to this procedure:

The troubleshooting procedures for the diagnostic codes of each temperature sensor are identical. The temperature sensors have two terminals. The signal line is connected to each sensor connector terminal 1. Terminal 2 is the return line. The signal voltage from terminal 1 of each sensor is supplied to the appropriate terminal in the P2/J2 connector or the P1/J1 connector.

Pull-up Voltage

The ECM continuously outputs a pull-up voltage on the circuit for the sensor signal wire. The ECM uses this pull-up voltage to detect an open in the signal circuit. When the ECM detects a voltage above a threshold on the signal circuit, an open circuit diagnostic code (XXX-3) is generated for the sensor.

If the sensor is disconnected, pull-up voltage at the connector indicates that the wires are not open or shorted to ground. If the sensor is disconnected, the absence of pull-up voltage indicates an open in the signal wire or a short to ground. If the sensor is disconnected and the voltage is different from pull-up voltage, the signal wire is shorted to another wire in the harness.

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Illustration 1	g06154862
Schematic for passive engine temperature sensors on the P2 connector

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Illustration 2	g01981034
Typical view of the P2 pin locations for the temperature sensors (8) NRS temperature sensor signal (9) Coolant temperature sensor signal (10) Fuel temperature sensor signal (19) Intake manifold air temperature sensor signal (56) Fuel temperature sensor and coolant temperature sensor ground (57) NRS temperature sensor and intake manifold air temperature sensor ground

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Illustration 3	g01170313
Typical view of an engine temperature sensor (1) Signal (2) Ground

For sensors that are connected to the P1/J1 connector, refer to the electrical schematic for the application.

For sensors that are connected to the P2/J2 connector, refer to Illustration 1.

Complete the procedure in the order in which the steps are listed.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Inspect Electrical Connectors and Wiring A. Thoroughly inspect the terminal connections on the ECM connectors and the engine temperature sensors. Refer to Troubleshooting, "Electrical Connectors - Inspect". B. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the sensor connectors that are associated with the active diagnostic code. C. Check the screw for the ECM connector for the correct torque of 6 N·m (53 lb in). D. Check the harness for corrosion, abrasion, and pinch points from the engine temperature sensors to the ECM.	Loose connection or damaged wire	Result: There is a fault in a connector or the wiring. Repair: Repair any faulty connectors or replace the wiring harness. Ensure that all the seals are properly in place and ensure that the connectors are correctly coupled. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: All connectors, pins, and sockets are correctly coupled and/or inserted. The harness is free of corrosion, abrasion, and pinch points. Proceed to Test Step 2.
2. Check the Type of Diagnostic Code that is Active A. Turn the keyswitch to the ON position. Wait at least 10 seconds for activation of the diagnostic codes. B. Use the electronic service tool to check for active diagnostic codes. Record all active diagnostic codes.	Diagnostic codes	Result: An XXXX-4 diagnostic code is active for one or more of the temperature sensors. Proceed to Test Step 3. Result: An XXXX-3 diagnostic code is active for one or more of the temperature sensors. Proceed to Test Step 5.
3. Create An Open Circuit at the Sensor Connector A. Turn the keyswitch to the OFF position. B. Disconnect the connector for the sensor with the XXXX-4 diagnostic code. C. Turn the keyswitch to the ON position. Wait for at least 10 seconds for activation of the diagnostic codes. D. Use the electronic service tool to check the "Active Diagnostic Code" screen. Check for an XXXX-3 diagnostic code.	Open circuit	Result: An XXXX-4 diagnostic code was active before disconnecting the sensor. An XXXX-3 diagnostic code became active after disconnecting the sensor. The sensor is faulty. Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Use the electronic service tool to verify that the repair eliminates the fault and then permanently install the new sensor. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The XXXX-4 diagnostic code is still active. Proceed to Test Step 4.
4. Check the Signal Wire for a Short Circuit A. Turn the keyswitch to the OFF position. B. Disconnect the P1 or P2 connector, as applicable, and disconnect the connector from the suspect sensor. C. Check the resistance between the applicable signal terminal on the P1/P2 connector and all other terminals on the P1/P2 connector. For sensors on the P1 connector, refer to the electrical schematic for the machine. For sensors on the P2 connector, refer to Illustration 1.	Greater than 100 Ohms	Result: At least one of the resistance measurements is less than 100 Ohms. The fault is in the engine harness. Repair: Repair the faulty connector or replace the faulty harness. Use the electronic service tool to verify that the repair eliminates the fault. Result: All resistance measurements are greater than 100 Ohms. Contact the Dealer Solutions Network (DSN).
5. Create a Short Circuit at the Sensor Connector A. Turn the keyswitch to the OFF position. B. Disconnect the connector for the suspect sensor. C. Fabricate a jumper wire that is 150 mm (6 inch) long. Crimp a terminal to both ends of the wire. D. Use the jumper to connect the sensor signal terminal to the sensor ground terminal on the harness connector for the suspect sensor. E. Turn the keyswitch to the ON position. Do not start the engine. F. Access the "Active Diagnostic Codes" screen on the electronic service tool and check for an active XXXX-4 diagnostic code for the suspect sensor. G. Remove the jumper. Reconnect the sensor.	Short circuit	Result: An XXXX-3 diagnostic code was active before installing the jumper. An XXXX-4 diagnostic code became active with the jumper installed - the sensor may be faulty. Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Use the electronic service tool to verify that the repair eliminates the fault and then permanently install the new sensor. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The XXXX-3 diagnostic code remains active when the jumper is installed. Proceed to Test Step 6.
6. Check the Signal Wire for an Open Circuit A. Turn the keyswitch to the OFF position. B. Disconnect the P1 or P2connector as applicable and disconnect the connector from the suspect sensor. C. Check the resistance between the applicable signal terminal on the sensor connector and the applicable terminal on the P1/P2 connector. For sensors on the P1 connector, refer to the electrical schematic for the machine. For sensors on the P2 connector, refer to Illustration 1.	Less than 2.0 Ohms.	Result: The resistance measurement is greater than 2.0 Ohms. The fault is in the engine harness. Repair: Repair the faulty wiring or replace the faulty wiring. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The resistance measurement is less than 2.0 Ohms. Contact the Dealer Solutions Network (DSN).