BIT 2681115 - Caterpillar

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Typical schematic
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P1 ECM connector (P1-4) 8 V supply (P1-5) Digital return (P1-11) Left exhaust temperature (P1-12) Right exhaust temperature
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Sensor connector (Pin A) Sensor supply (Pin B) Sensor return (Pin C) Signal
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Left side view (1) Left exhaust temperature sensor
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Right side view (2) Right exhaust temperature sensorTest Step 1. Check for an "Active" Diagnostic Code
Connect Caterpillar Electronic Technician (ET) to the service tool connector.
Turn the breaker for the ECM to the ON position.
Turn the switch that provides power to the keyswitch input for the ECM to the ON position.
Monitor the diagnostic codes on Cat ET. Check and record any diagnostic codes.Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
Determine if a diagnostic code has occurred several times.Note: A diagnostic code that is logged several times is an indication of an intermittent problem. Most intermittent problems are the result of a bad connection between a socket and a pin in a connector or a bad connection between a wire and a terminal.
Determine if a -8 diagnostic code is active for one of the exhaust temperature sensors.Expected Result:No diagnostic code is active for the exhaust temperature sensors.Results:
OK - No diagnostic codes are active.Repair: If the problem is intermittent, refer to Troubleshooting, "Inspecting Electrical Connectors" for the correct procedures for inspecting electrical connectors.STOP
Not OK - A -8 diagnostic code is active or the diagnostic code is logged several times. Proceed to Test Step 2.Test Step 2. Check the Digital Supply Voltage at the Sensor Connector
Disconnect the suspect sensor(s) at the sensor connector:
Measure the voltage on the ECM side of the sensor connector between pin A and pin B for the suspect sensor(s).Expected Result:The supply voltage is 8.0 0.4 VDC.Results:
OK - The supply voltage is 8.0 0.4 VDC. Proceed to Test Step 4.
Not OK - The supply voltage is not 8.0 0.4 VDC. Proceed to Test Step 3.Test Step 3. Check the Digital Supply Voltage at the ECM
Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
Turn the breaker for the ECM to the OFF position.
Remove the supply wire from P1-4. Install a wire jumper into the socket for P1-4.
Turn the breaker for the ECM to the ON position.
Turn the switch that provides power to the keyswitch input for the ECM to the ON position.
Measure the voltage between the wire jumper in terminal P1-4 and engine ground.
Turn the breaker for the ECM to the OFF position.
Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
Remove the wire jumper and reconnect all wires. Reconnect ECM connector J1/P1.Expected Result:The supply voltage is 8.0 0.4 VDC.Results:
OK - The supply voltage is 8.0 0.4 VDC. The supply voltage at the ECM is correct. There is a problem in the wiring between the ECM and the sensor connector. Repair the connectors or wiring and/or replace the connectors or wiring.Repair: Repair the connectors or wiring and/or replace the connectors or