System Operation Description:
Use this procedure to troubleshoot the electrical system if a problem is suspected with a sensor supply. Use this procedure if any one of the diagnostic codes in Table 1 is active or easily repeated.
Note: Some of the following codes may not be applicable for certain applications.
| Diagnostic Codes Table | |||
|---|---|---|---|
| CDL Code | J1939 Code | Code Description | Comments |
| 41-3 | 678-3 | 8 VDC Supply : Voltage Above Normal | The code is logged. |
| 41-4 | 678-4 | 8 VDC Supply : Voltage Below Normal | The code is logged. |
| 262-3 | 3509-3 | 5 Volt Sensor DC Power Supply : Voltage Above Normal | The code is logged. All sensors are set to default values. |
| 262-4 | 3509-4 | 5 Volt Sensor DC Power Supply : Voltage Below Normal | The code is logged. All sensors are set to default values. |
| 274-21 | 108-21 | Atmospheric Pressure Sensor : Data Drifted Low | The code is logged. The 5 VDC supply to the sensor has been lost. |
| 289-21 | 5578-21 | Fuel Pressure Sensor – Before Fuel Filter : Data Drifted Low | The code is logged. The 5 VDC supply to the sensor has been lost. |
| 460-21 | 5580-21 | Fuel Pressure Sensor – After Fuel Filter : Data Drifted Low | The code is logged. The 5 VDC supply to the sensor has been lost. |
| 1785-21 | 3563-21 | Intake Manifold Pressure Sensor : Data Drifted Low | The code is logged. The 5 VDC supply to the sensor has been lost. |
| 2131-3 | 3510-3 | 5 v Sensor DC Power Supply #2 : Voltage Above Normal | The code is logged. Engine power may be derated. |
| 2131-4 | 3510-4 | 5 v Sensor DC Power Supply #2 : Voltage Below Normal | The code is logged. Engine power may be derated. |
| 3385-21 | 3358-21 | EGR Intake Pressure Sensor : Data Drifted Low | The code is logged. The 5 VDC supply to the sensor has been lost. |
| 3464-21 | 3609-21 | DPF #1 Intake Pressure Sensor : Data Drifted Low | The code is logged. The 5 VDC supply to the sensor has been lost. |
| 3493-21 | 3837-21 | Aftertreatment #1 Secondary Air Pressure Sensor : Data Drifted Low | The code is logged. The 5 VDC supply to the sensor has been lost. |
System Operation
The Electronic Control Module (ECM) supplies a regulated voltage of 5.0 ± 0.2 VDC to the sensors.
The supply voltage for the sensors is routed from the ECM to terminal 1 of each sensor connector. The sensor return for the sensors is routed from the ECM to terminal 2 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.
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 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.
Illustration 1 g01240891
Sensor connector
(1) 5 V or 8 V sensor supply
(2) Sensor return
(3) Signal
| Sensor Supply | Sensor Supply ECM Location |
| Sensor Supply #1 | Sensors on the engine ECM J2 connector |
| Sensor Supply #2 | Sensors on the engine ECM J1 connector |
Illustration 2 g03450476
Typical schematic
The signal wires are not shown in Illustration 2.
Note: The diagram above is a simplified schematic of the ECM – relay circuit. The schematic is electrically correct. However, not all of the possible sensors or harness connectors are shown. Refer to the latest revision of the Electrical Schematic for the complete schematic for your application.
| Troubleshooting Test Steps | Values | Results |
| 1. Determine the CodeA. Connect Cat ET to the service tool connector. Refer to Troubleshooting, “Electronic Service Tools”, if necessary.
B. Turn the keyswitch to the ON position. C. Determine if a diagnostic trouble code is present. |
Diagnostic Codes | Result: A -3 or -4 code is present.Note which ECM is reporting the active sensor supply code.
Proceed to Test Step 2. Result: A -21 code is present. Proceed to Test Step 3. |
| 2. Check for a Failed Sensor A. Connect to Cat ET.B. Turn the keyswitch to the ON position. C. Disconnect a sensor on the suspect sensor supply circuit. D. Monitor Cat ET while the sensor is disconnected to see if the active code changes to logged. E. Connect the suspect sensor to the wiring harness F. Repeat steps C through E for each sensor on the suspect sensor supply. |
Failed Sensor | Result: The suspect sensor supply active code changes to logged when a sensor is unplugged.Replace the failed sensor.
Verify that the repair resolved the problem. Result: The suspect sensor supply active code remains active after all sensors on the sensor supply circuit have been checked. A failed wiring harness has been detected. Repair or replace the wiring harness. Verify that the repair resolved the problem. |
| 3. Check the Sensor SupplyA. Turn the keyswitch to the OFF position.
B. Unplug the suspect sensor from the wiring harness. C. Place a jumper wire between pin 1 and pin 2 on the suspect sensor wiring harness connector. D. Connect to Cat ET. E. Turn the keyswitch to the ON position. F. Monitor the diagnostic codes using Cat ET. |
Diagnostic Codes | Result: A -4 code is activated on the suspect sensor supply.Remove the sensor. Check the sensor passage for a blockage or obstruction. Also, check for moisture frozen in the lines.
If blockage is not found, replace the sensor. Verify that the repair resolved the problem. Result: A -4 code is not activated on the suspect sensor supply. The problem is in the wiring from the ECM to the sensor connector. Repair the wiring or replace the wiring. Verify that the repair resolved the problem. |
Test Step 1.
Complete the procedure in the order in which the steps are listed.
Results:
- The procedure corrected the issue. – STOP
- The procedure did not correct the issue. –Repair: Contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).STOP