C27 and C32 Engines for Caterpillar Built Machines Caterpillar

Sensor Supply - Test

Usage:

990K A9P

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

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Table 1
Diagnostic Codes
CDL Code	Code Description	Comments
41-3	8 Volt DC Supply : Voltage Above Normal	The code is logged. The digital sensor is set to the default value.
41-4	8 Volt DC Supply : Voltage Below Normal
262-3	5 Volt Sensor DC Power Supply : Voltage Above Normal	The code is logged. All sensors are set to default values.
262-4	5 Volt Sensor DC Power Supply : Voltage Below Normal	The code is logged. All sensors are set to default values.
460-21	Fuel Pressure Sensor - After Fuel Filter : Data Drifted Low	The code is logged. The sensor is set to the default value.
1785-21	Intake Manifold Pressure Sensor : Data Drifted Low	The code is logged. The sensor is set to the default value.
2131-3	5 Volt Sensor DC Power Supply #2 : Voltage Above Normal	The code is logged. Engine power may be derated.
2131-4	5 Volt Sensor DC Power Supply #2 : Voltage Below Normal	The code is logged. Engine power may be derated.
3385-21	EGR Intake Pressure Sensor : Data Drifted Low	The code is logged. The sensor is set to the default value.

System Operation

The Electronic Control Module (ECM) supplies a regulated voltage of 5.0 ± 0.2 VDC to the following sensors:

Aftertreatment ID module
Atmospheric pressure sensor
Buffer for the exhaust temperature sensors (left side)
Buffer for the exhaust temperature sensors (right side)
Crankcase pressure sensor
Engine oil pressure sensor
Fuel pressure sensor (filtered fuel pressure)
Intake manifold pressure sensor
NRS absolute pressure sensor
NRS differential pressure sensor
Turbocharger inlet pressure sensor

The ECM supplies a regulated voltage of 8.0 ± 0.4 VDC to the following sensor:

Engine oil level sensor
Decelerator position sensor

The supply voltage for the sensors is routed from the ECM to terminal 1, or terminal A of each sensor connector. The sensor return for the sensors is routed from the ECM to terminal 2, or terminal B of the sensor connector.

The -21 code becomes active when the ECM determines that the 5 V supply is missing at the pressure sensor. The ECM sets the value of the suspect sensor to the default value.

The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.

Note: The sensors are not protected from overvoltage. A short from the supply line to the +Battery may damage the sensors. If any of the three diagnostic codes are active, a sensor may have been damaged. Repair the sensor supply and check for any active sensor diagnostic codes in order to determine if a sensor has been damaged.

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Illustration 1	g02151686
Schematic of the circuits for the analog sensor supplies

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Illustration 2	g02315596
Schematic of the circuits for the digital sensor supply

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Table 2
Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Turn the keyswitch to the OFF position. B. Thoroughly inspect the connectors. Refer to Troubleshooting, "Electrical Connectors-Inspect" for additional information. C. Perform a 45 N (10 lb) pull test on the connector wires. D. Check the harness for abrasions and pinch points.	Connectors and Wiring	Result: The connectors and wiring appear to be OK. Proceed to Test Step 2. Result: There is a problem with the connectors and/or wiring. Repair: Repair or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. If the problem is not resolved, proceed to Test Step 2.
2. Check for Codes A. Connect Cat^® Electronic Technician (ET) to the service tool connector. B. Determine if a code is active or logged.	41-3, 41-4 262-3, 262-4, 460-21, 2131-3, 2131-4, 3385-21	Result: No diagnostic codes are active or logged. There does not appear to be an electrical problem with the sensor supply at this time. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect". Result: Either the 41-3 or 41-4 diagnostic code is active or logged at this time. There is an electrical problem with the digital sensor supply. Proceed to Test Step 6. Result: A -21 diagnostic code is logged at this time. The analog supply is not reaching the suspect sensor or there is a problem with the sensor. Proceed to Test Step 3. Result: Either the 2131-3 or 2131-4 diagnostic code is active or logged at this time. There is an electrical problem with the analog sensor supply. Proceed to Test Step 4.
3. Check the Supply Voltage at the Sensor Connector A. Disconnect the harness connectors for the following sensors: · Fuel pressure sensor (filtered fuel pressure) · NRS absolute pressure sensor B. Restore the electrical power to the ECM. Note: Be sure to wiggle the harness during the following measurements in order to reveal an intermittent condition. C. Measure the voltage between terminals 1 and 2 at the appropriate sensor connector. D. Remove the electrical power from the ECM. E. Connect all of the sensors.	5.0 ± 0.2 VDC	Result: Each voltage measurement is 5.0 ± 0.2 VDC. Repair: The analog supply is reaching the sensor connector. There may be a problem with the sensor. Perform the following procedure: 1. Clear all diagnostic codes. 2. Run the engine. Allow the engine to warm up. Check if the code has been logged again. If the code becomes active or logged, the sensor is faulty. Replace the sensor. Verify that the repair eliminates the original problem. If the code does not become active or logged, there may be an intermittent problem in the harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct troubleshooting procedure. If the repair does not eliminate the problem, proceed to Test Step 3. Result: At least one voltage measurement is not 5.0 ± 0.2 VDC. There is a problem with the harness wiring or with the ECM. Proceed to Test Step 5.
5. Disconnect the Analog Sensors While You Check for Active Diagnostic Codes A. Restore the electrical power to the ECM. B. Monitor the active diagnostic code screen on Cat ET while you disconnect each 5 v sensor at the sensor connector. Check for an active 262-3, 262-4, 2131-3, or 2131-4. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. a. Disconnect the following sensors one at a time: · Aftertreatment ID module · Atmospheric pressure sensor · Buffer for the exhaust temperature sensors (left side) · Buffer for the exhaust temperature sensors (right side) · Crankcase pressure sensor · Engine oil pressure sensor · Fuel pressure sensor (filtered fuel pressure) · Intake manifold pressure sensor · NRS absolute pressure sensor · NRS differential pressure sensor · Turbocharger inlet pressure sensor C. Remove the electrical power from the ECM. Restore the wiring to the original configuration.	Code	Result: The 262-3, 262-4, 2131-3, or 2131-4 diagnostic code deactivates when a particular sensor is disconnected. Repair: Connect the suspect sensor. If the code returns, replace the sensor. Connect all of the connectors. Verify that the problem is resolved. Result: The 262-3, 262-4, 2131-3, or 2131-4 diagnostic code remains active after all of the sensors are disconnected. The sensors are not the cause of the diagnostic code. Leave the sensors disconnected. Proceed to Test Step 5.
5. Check the 5 V Supply Voltages at the ECM A. Disconnect the J2/P2 and J2/P2 ECM connectors. B. Fabricate eight jumper wires that are long enough to be used to measure the supply voltage at the ECM connector. Crimp connector sockets to one end of each jumper wire. C. Remove the wires from the following terminal locations: · P1-2 (analog sensor supply · P1-3 (analog sensor return · P2-30 (analog sensor return · P2-72 (analog sensor supply · P2-81 (analog sensor supply · P2-82 (analog sensor supply · P2-83 (analog sensor return · P2-92 (analog sensor return Install a jumper wire into each of these terminal locations. D. Connect the J2/P2 ECM connector. Note: Ensure that the loose ends of the jumper wires do not contact any ground source. E. Restore electrical power to the engine ECM. F. Measure the voltage between the jumper wires in the following terminal locations: · P1-2 and P1-3 · P2-72 and P2-83 · P2-81 and P2-30 · P2-82 and P2-92 G. Remove electrical power from the ECM. Restore the wiring to the original configuration.	5.0 ± 0.2 VDC	Result: The voltage measurement is 5.0 ± 0.2 VDC. Repair: The ECM is operating correctly. The supply wire that is in the harness is shorted to another wire in the harness or the supply wire is shorted to engine ground. There may be an open in wiring that is in the harness. Repair the harness. If the repair does not resolve the problem, proceed to Test Step 6. Result: The voltage measurement is not 5.0 ± 0.2 VDC. Repair: The ECM does not appear to be generating the correct supply voltage. There may be a problem with the ECM. Before you consider replacing the ECM, consult the Dealer Solutions Network (DSN) for assistance.
6. Disconnect the Digital Sensors while you Check for Active Diagnostic Codes A. Restore the electrical power to the ECM. B. Disconnect the throttle position sensor at the throttle pedal. C. Monitor the active diagnostic code screen on Cat ET while you disconnect the throttle position sensor at the sensor connector. Check for an active 41-3 code or an active 41-4 code. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. D. Remove electrical power from the ECM. Restore the wiring to the original configuration.	Codes	Result: The 41-3 or 41-4 diagnostic code deactivates when the throttle position sensor is disconnected. Repair: Connect the suspect sensor. If the code returns, replace the sensor. Connect all of the connectors. Verify that the problem is resolved. If the repair does not resolve the problem, proceed to Test Step 7. Result: The 41-3 or 41-4 diagnostic code remains active after the sensor is disconnected. Leave the sensor disconnected. The sensor is not the cause of the diagnostic code. Proceed to Test Step 7.
7. Check the 8 V Supply Voltage at the ECM A. Disconnect the J1/P1 ECM connector. B. Fabricate two jumper wires that are long enough to be used to measure the supply voltage at the ECM connectors. Crimp connector sockets to one end of each jumper wire. C. Remove the wires from terminal locations P1-4 (digital sensor supply) and P1-5 (digital return). Install a jumper wire into each of these terminal locations. D. Connect the J1/P1 ECM connector. E. Restore electrical power to the engine ECM. F. Measure the voltage between the jumper wire in P1-4 (digital sensor supply) and P1-5 (sensor return). G. Remove electrical power from the ECM. Restore the wiring to the original configuration.	8.0 ± 0.4 VDC	Result: The voltage measurement is 8.0 ± 0.4 VDC. The ECM is operating correctly. Repair: The supply wire is shorted to another wire in the harness or the supply wire is shorted to engine ground. There may be an open in the wiring that is in the harness. Repair the supply wire. Verify that the repair eliminated the problem. Result: The voltage measurement is not 8.0 ± 0.4 VDC. Repair: The ECM does not appear to be generating the correct supply voltage. There may be a problem with the ECM.Before you consider replacing the ECM, consult the Dealer Solutions Network (DSN) for assistance.