System Operation Description:
The Electronic Control Module (ECM) supplies a regulated voltage of 5.0 ± 0.5 VDC to the following sensors:
- Atmospheric pressure sensor
- Auxiliary pressure sensor
- Engine oil pressure sensor
- Fuel pressure sensor
- Turbocharger outlet pressure sensor
The supply for the +5 V engine pressure sensor is routed from the ECM to terminal A of each pressure sensor connector. The supply voltage is 5.0 ± 0.16 VDC.
The +5 V diagnostic code is probably caused by a short circuit to ground or a short circuit to another voltage source in the harness.
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| Illustration 1 | g00750045 |
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Schematic |
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| Illustration 2 | g00763287 |
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J2/P2 ECM connector |
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| Illustration 3 | g00763353 |
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J1/P1 ECM connector |
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Test Step 1. Disconnect the ECM Connectors
- Turn the keyswitch to the OFF position.
- Connect the Caterpillar Electronic Technician (Cat ET) to the service tool connector.
- Disconnect the P1 ECM connector and the P2 ECM connector from the ECM.
- Check the connectors for corrosion and for moisture.
- Connect a 140-2266 Cable (Seventy-Pin Breakout) at the J1/P1 ECM connector.
- Turn the keyswitch to the ON position.
- Check for active diagnostic codes on Cat ET.
Note: An open circuit diagnostic code should be active for all of the engine pressure sensors.
Expected Result:
The 5 volt diagnostic codes are not active. An open circuit diagnostic code is active for all of the engine pressure sensors.
Results:
- OK – The 5 volt diagnostic codes are not active.
Repair: Reconnect the P2 ECM connector. Remove the breakout T. Reconnect the P1 ECM connector.
Proceed to Test Step 2.
- Not OK – The 5 volt diagnostic codes are still active.
Repair: Connect a test ECM.If the test ECM fixes the problem, reconnect the suspect ECM.If the problem returns, permanently install the new ECM.Verify that the repair eliminates the problem.
STOP
Test Step 2. Disconnect the Sensors
- Turn the keyswitch to the ON position.
- Monitor the active diagnostic code screen on Cat ET.
- Disconnect the pressure sensors one at a time. Wait for 30 seconds after each pressure sensor is disconnected.
Note: The 5 volt diagnostic code will become inactive if a pressure sensor is the cause of the 5 volt diagnostic code.
- Ensure that all of the pressure sensors are disconnected.
Expected Result:
The 5 volt diagnostic code is still active when all of the pressure sensors are disconnected.
Results:
- OK – The 5 volt diagnostic code is still active.
Repair: Leave all of the pressure sensors disconnected.
Proceed to Test Step 4.
- Not OK – The 5 volt diagnostic code disappears when the pressure sensors are disconnected.
Repair: Reconnect all of the pressure sensors except the suspect sensor.
Proceed to Test Step 3.
Test Step 3. Check the Signal Wire
- Turn the keyswitch to the ON position.
Note: The suspect sensor should be disconnected.
- Measure the voltage between terminal C (Signal) and terminal B (Common) of the connector for the suspect sensor on the engine harness.
Expected Result:
The voltage is less than 7.0 VDC.
Results:
- OK – The voltage is less than 7.0 VDC.
Repair: Temporarily connect a new sensor.If the problem is resolved with the new sensor, reconnect the suspect sensor.If the problem returns, replace the suspect sensor.Verify that the repair eliminates the problem.
STOP
- Not OK – The voltage is greater than 7.0 VDC.
Repair: Inspect the signal wire for a short circuit to a voltage source.Repair the signal wire or replace the signal wire.Verify that the repair eliminates the problem.
STOP
Test Step 4. Determine the Condition that is Present
- Turn the keyswitch to the ON position.
- Access the active diagnostic code screen on Cat ET.
Expected Result:
262-03 or 262-04 is active.
Results:
- 262-03 – Proceed to Test Step 5.
- 262-04 – Proceed to Test Step 7.
Test Step 5. Measure the 5 Volt Supply to the Sensor
- Turn the keyswitch to the ON position.
Note: All of the pressure sensors should be disconnected.
- Measure the voltage between terminal A (+5V) and chassis ground for each pressure sensor.
Expected Result:
The voltage is 5.0 ± 0.16 VDC.
Results:
- OK – The 5 volt supply is within the range. Proceed to Test Step 6.
- Not OK – The voltage is greater than 5.16 volts.
Repair: Check the 5 volt supply wire for a short to a higher voltage source.Repair the 5 volt supply wire or replace the 5 volt supply wire.Verify that the repair eliminates the problem.
STOP
Test Step 6. Check the Common Wire
- Turn the keyswitch to the ON position.
- Measure the voltage between terminal A (+5V) and terminal B (Common) on all of the pressure sensors.
- While the voltage is monitored, perform a 45 N (10 lb) pull test on the common wires for the 5 volt supply.
- P2:3 (Common)
- P1:3 (Common)
Expected Result:
The voltage is 5.0 ± 0.16 VDC.
Results:
- OK – The voltage is within the range.
Repair: If the problem is intermittent, refer to Troubleshooting, “Electrical Connectors – Inspect”.
STOP
- Not OK – The voltage is not within the range.
Repair: Inspect the common wire for an open circuit.Repair the common wire or replace the common wire.Verify that the repair eliminates the problem.
STOP
Test Step 7. Check the Resistance of the Harness
- Turn the keyswitch to the OFF position.
- Verify that all of the sensors are disconnected.
- Measure the resistance between terminal A (+5V) and terminal B (Common) of each pressure sensor connector.
Expected Result:
The resistance is greater than 20,000 Ohms, or “OL” is displayed on the multimeter.
Results:
- OK – The 5 volt supply and the pressure sensor common are not shorted.
Repair: Check the 5 volt supply for a short to ground.Repair the 5 volt supply wire or replace the 5 volt supply wire.Verify that the repair eliminates the problem.
STOP
- Not OK – There is a short between the 5 volt supply and the pressure sensor common.
Repair: Locate the short between the 5 volt supply and the pressure sensor common.Repair the wiring or replace the wiring.Verify that the repair eliminates the problem.
STOP