PUSH ARM AS 4T6734 - Caterpillar

System OperationUse this procedure to troubleshoot any suspect problems with the following sensors:
Left exhaust temperature sensor
Right exhaust temperature sensorThe PWM sensors provide a signal to the engine's ECM for certain engine operating conditions. The sensors receive a 8.0 0.4 VDC regulated voltage from the ECM.The sensor's wires are routed from the ECM to the sensor connectors. The following list gives the terminal locations for the sensor connector.
Terminal A 8 V supply
Terminal B sensor return
Terminal C sensor signalThe ECM performs an automatic calibration of these sensors whenever the ECM is powered and the engine has been off for at least five seconds.The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.
Illustration 1 g01242175
Typical schematic
Illustration 2 g01242178
P1 ECM connector
(P1-4) 8 V supply
(P1-5) Digital return
(P1-11) Left exhaust temperature
(P1-12) Right exhaust temperature
Illustration 3 g01242179
P2 ECM connector
(P2-56) 8 V supply
(P2-66) Digital return
Illustration 4 g01234146
Location of ECM connectors
Illustration 5 g01243506
Sensor connector
(Pin A) Sensor supply
(Pin B) Sensor return
(Pin C) Signal
Illustration 6 g01242181
Rear view
(1) Left exhaust temperature sensor
(2) Right exhaust temperature sensor Test Step 1. Check for an "Active" Diagnostic Code
Connect Caterpillar Electronic Technician (ET) to the service tool connector.
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
Remove electrical power from the ECM.
Remove the supply wire from P1-4 or from P2-56. Install a wire jumper into the socket for the supply wire.
Restore electrical power to the ECM.
Measure the voltage between the wire jumper and engine ground.
Remove electrical power from the ECM.
Remove the wire jumper. 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