0321239 JOHNSON PISTON,Letdown control

Illustration 1 g01852233
Schematic
Illustration 2 g00886096
P1 ECM ConnectorTest Step 1. Inspect Electrical Connectors and Wiring
Turn the keyswitch to the OFF/RESET position.
Thoroughly inspect ECM connector J1/P1, customer connector J3/P3, and all other connectors in the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Verify that all wires that are associated with the analog sensors are connected in the correct location.Expected Result:All connectors, pins, and sockets should be completely inserted and coupled. The harness and wiring should be free of corrosion, abrasion, and pinch points. All connections and grounds should be tight and free of corrosion.Results:
OK - Proceed to Test Step 2.
Not OK - Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 2. Check Power Supply to the ECM
Connect the Caterpillar Electronic Technician (Cat ET) to the service tool connector.
Turn the keyswitch to the ON position.
Monitor "Battery Voltage" on the status screen of Cat ET.Expected Result:The ECM is receiving the correct voltage from the battery.Results:
OK - The ECM is receiving the correct voltage from the battery. Proceed to Test Step 3.
Not OK - The ECM is not receiving the correct voltage from the battery.Repair: Troubleshoot the ECM power supply before continuing with this test.STOPTest Step 3. Check the Analog Sensors for Internal Shorts
Turn the keyswitch to the OFF/RESET position and install a 7X-1715 Adapter Cable (40-Pin Breakout T) at the J1/P1 ECM connector.
Turn the keyswitch to the ON position.
Measure the voltage across terminal 36 (Analog Sensor +5V) and terminal 30 (Sensor Return) of the breakout T.
Monitor the voltage while you disconnect each analog sensor.Expected Result:The analog sensor supply voltage will increase to 5 0.5 VDC when the bad sensor is disconnected.Results:
OK - One of the sensors appear to be internally shorted.Repair: Temporarily connect a new sensor.Verify that the replacement sensor solves the problem before you permanently install the new sensor.STOP
Not OK - None of the analog sensors are internally shorted. Leave the sensors disconnected. Proceed to Test Step 4.Test Step 4. Check the Analog Sensor Supply Voltage at the Sensor Connectors
Turn the keyswitch to the OFF/RESET position.
Reconnect the J1/P1 ECM connector.
Turn the keyswitch to the ON position.
Measure the voltage across terminal A (+5V Analog) and terminal B (Sensor Return) on the harness side of each sensor connector.Expected Result:The analog sensor supply voltage should be 5.0 0.5 VDC at each sensor connector.Results:
OK - The supply voltage is reaching the sensors. The circuit appears to be working correctly at this time.Repair: If the problem is intermittent refer to Troubleshooting, "Electrical Connectors - Inspect".STOP
Not OK - The supply voltage is not reaching the sensors. Leave the sensors disconnected. Proceed to Test Step 5.Test Step 5. Check for Shorts in the Harness
Turn the keyswitch to the OFF/RESET position.
Disconnect the J1/P1 ECM connector and all of the analog sensors.
Measure the resistance between P1:36 (Analog Sensor +5V) and P1:30 (Analog Sensor Return).
Measure the resistance between P1:36 (Analog Sensor +5V) and engine ground.Expected Result:The resistance should be greater than 20,000 Ohms.Results:
OK - Proceed to Test Step 6.
Not OK - There is a short between the ECM and the analog sensors.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 6. Check the Analog Sensor Supply Voltage at the ECM
Turn the keyswitch to the OFF/RESET position.
Remove the wires from P1:36 (Analog Sensor +5V) and P1:30 (Sensor Return).
Turn the keyswitch to the ON position.
Measure the voltage across P1:36 (Analog Sensor +5V) and P1:30 (Sensor Return) at the P1 ECM connector.Expected Result:The supply voltage should be 5.0 0.5 VDC.Results:
OK - The ECM is supplying the correct voltage, but there is an open in the harness between the ECM and the analog sensors.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOP
Not OK - The ECM is not supplying the correct voltage.Repair: Verify your results.Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.Verify that the repair eliminates the problem.STOP