C27 and C32 Engines for Caterpillar Built Machines Caterpillar

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

Table 1

CDL Code	Code Description	Comments
110-3 Engine Coolant Temperature Sensor : Voltage Above Normal	The Electronic Control Module (ECM) detects a signal voltage that is not in the acceptable range.	The code is logged. The -3 code will become active after 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 a signal voltage that is not in the acceptable range.	The code is logged. 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.
172-3 Intake Manifold Air Temperature Sensor : Voltage Above Normal	The ECM detects a signal voltage that is not in the acceptable range on the left side manifold.	The code is logged. The ECM flags the intake manifold air temperature as invalid data and the intake manifold air temperature is set to a default value of 40 °C (104 °F).
172-4 Intake Manifold Air Temperature Sensor : Voltage Below Normal	The ECM detects a signal voltage that is not in the acceptable range on the left side manifold.
174-3 Fuel Temperature Sensor : Voltage Above Normal	The ECM detects a signal voltage that is not in the acceptable range.	The code is logged. The ECM flags 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 a signal voltage that is not in the acceptable range.
1796-3 Intake Manifold #2 Air Temperature Sensor : Voltage Above Normal	The ECM detects a signal voltage that is not in the acceptable range on the right side manifold.	The code is logged. The ECM flags the intake manifold temperature as invalid data and the intake manifold temperature is set to a default value.
1796-4 Intake Manifold #2 Air Temperature Sensor : Voltage Below Normal	The ECM detects a signal voltage that is not in the acceptable range on the right side manifold.
2526-3 Air Inlet Temperature Sensor : Voltage Above Normal	The ECM detects a signal voltage that is not in the acceptable range.	The code is logged.
2526-4 Air Inlet Temperature Sensor : Voltage Below Normal	The ECM detects a signal voltage that is not in the acceptable range.	The code is logged.
3386-3 EGR Temperature Sensor : Voltage Above Normal	The ECM detects a signal voltage that is not in the acceptable range.	The code is logged.
3386-4 EGR Temperature Sensor : Voltage Below Normal	The ECM detects a signal voltage that is not in the acceptable range.	The code is logged.

System Overview

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.

Diagnostics on the Caterpillar Electronic Technician (ET)

Wiggle Test - The Wiggle Test allows you to monitor the status of the signals from the sensors.

For additional information regarding the Wiggle Test, refer to the documentation that accompanies the Cat ET software.

Illustration 1	g02133854
Schematic for the passive sensors

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

Table 2

Troubleshooting Test Steps	Values	Results
1. Check for Codes A. Connect Cat ET to the service tool connector. B. Look for these active codes or logged codes: · -3 · -4 Note: The engine must be running for 7 minutes in order for a 110-3 code to become active.	Codes	Result: A diagnostic code is logged. Proceed to Test Step 4. Result: A -3 diagnostic code is active. Proceed to Test Step 2. Result: A -4 diagnostic code is active. Proceed to Test Step 3.
2. Create a Short at the Sensor Connector A. Turn the keyswitch to the OFF position. B. Disconnect the suspect sensor. C. Install the jumper wire between terminal 1 (sensor signal) and terminal 2 (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: The engine must be running for 7 minutes in order for a 110-3 code to become active. F. Turn the keyswitch to the OFF position.	-3, -4 Code	Result: The -3 diagnostic code remains active for the suspect sensor. Repair: There is an open in the harness. Repair the wiring or replace the harness. Verify that the problem is resolved. If the repair does not resolve the problem, proceed to Test Step 3. Result: A -4 diagnostic code became active after creating the short at the sensor connector. Repair: The wiring is OK. Replace the sensor. Verify that the problem is resolved. If the repair does not resolve the problem, proceed to Test Step 3.
3. 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: The engine must be running for 7 minutes in order for a 110-3 code to become active. E. Turn the keyswitch to the OFF position.	-3, -4 Code	Result: The -4 diagnostic code remains active for the suspect sensor. Repair: There is a short in the harness. Repair the wiring or replace the harness. Verify that the problem is resolved. If the repair does not resolve the problem, proceed to Test Step 4. Result: A -3 diagnostic code became active after disconnecting the sensor. Repair: The wiring is OK. Replace the sensor. Verify that the problem is resolved. If the repair does not resolve the problem, proceed to Test Step 4.
4. Perform the Wiggle Test A. Turn the keyswitch to the ON position. B. Use Cat ET to run the "Wiggle Test". C. Slowly wiggle the wiring and the connectors between the P2 connector and the sensor. Slowly wiggle the wiring and the connectors between the P1 connector and the sensor. Pay particular attention to the wiring near each connector. Be sure to wiggle all of the wiring. Look for the following problems: · Loose connectors or damaged connectors · Moisture on the connectors or the wiring · Damage that is caused by excessive heat · Damage that is caused by chafing · Improper routing of wiring · Damaged insulation	Wiggle Test	Result: The wiring failed the wiggle test. Repair: There is a problem with the wiring. Repair the wiring or replace the wiring. Verify that the problem is resolved. Result: The wiring passed the Wiggle Test. Repair: The problem may be intermittent. Inspect the wiring. Refer to Troubleshooting, "Electrical Connectors - Inspect". If the wiring is OK, perform the following procedure: 1. Turn the keyswitch to the OFF position. 2. Disconnect the connectors. Carefully inspect the terminals for proper installation. Ensure that each terminal is clean and dry. 3. Insert a pin into each socket. Verify that each socket grips the pin firmly. Repair any problems. 4. Connect all connectors. Verify that the problem is resolved.