CAP 0812963 - Caterpillar

Note: The following conditions must exist before any of the above codes will become active:
The ECM has been powered for at least 2 seconds.
There are no active 168-X diagnostic codes.The ECM will log the diagnostic code. If equipped, the warning light will come on.The following background information is related to this procedure:The troubleshooting procedures for the diagnostic codes of each temperature sensor are identical. The temperature sensors have two terminals. The signal line is connected to each sensor connector terminal 1. Terminal 2 is the return line. The signal voltage from terminal 1 of each sensor is supplied to the appropriate terminal in the P2/J2 connector or the P1/J1 connector.Pull-up VoltageThe ECM continuously outputs a pull-up voltage on the circuit for the sensor signal wire. The ECM uses this pull-up voltage in order to detect an open in the signal circuit. When the ECM detects a voltage above a threshold on the signal circuit, an open circuit diagnostic code (XXX-3) is generated for the sensor.If the sensor is disconnected, pull-up voltage at the connector indicates that the wires are not open or shorted to ground. If the sensor is disconnected, the absence of pull-up voltage indicates an open in the signal wire or a short to ground. If the sensor is disconnected and the voltage is different from pull-up voltage, the signal wire is shorted to another wire in the harness.
Illustration 1 g03374886
Schematic for passive engine temperature sensors on the P2 connector
Note: For information regarding sensors that are connected to the P1 connector, refer to the Electrical Schematic for the application.
Illustration 2 g03374910
P2 pin locations for the temperature sensors
(37) Sensor ground
(42) Intake manifold air temperature sensor signal
(43) Coolant temperature sensor signal
Illustration 3 g01170313
Typical view of an engine temperature sensor
(1) Signal
(2) Ground
Table 2
Troubleshooting Test Steps Values Results
1. Check for Diagnostic Trouble Codes
A. Connect to the electronic service tool.
B. Turn the keyswitch to the ON position.
C. Access the "Active Diagnostic Code" screen on the electronic service tool.
Wait at least 30 seconds in order for the diagnostic codes to become active.
D. Look for one of the diagnostic codes that are listed in Table 1.
Codes
Result: A -3 diagnostic code is active.
Proceed to Test Step 2.
Result: