PLATE 4Z9070 - Caterpillar

Illustration 1 g02025091
Ambient Air Temperature sensor circuit schematic
This diagnostic code is for the Ambient Air Temperature sensor. An FMI 03 diagnostic code means the machine ECM has determined the sensor output signal voltage is above the normal limit. Possible causes of this diagnostic code are:
Failed sensor power supply.
Failed sensor.
Open sensor circuit wire.
Sensor signal output wire shorted to +battery.
Failed machine ECM, but most unlikely.Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes now, but clear those codes after the original diagnostic code has been corrected. Note: Poor connections are often the cause of a problem in electrical circuits. Before performing this procedure, inspect all of the harness connectors involved in the circuit. Verify that all of the connections in the circuit are clean, secure, and in good condition. If a problem is found with any of the connections: correct the problem and verify that diagnostic code CID 0171 FMI 03 is still active, before performing the following procedures. System Response:This failure may cause ambient air temperature to indicate the maximum temperature. The failure may also cause hydraulic oil temperature to indicate the maximum temperature, intermittently. Test Step 1. VERIFY THE +8 DCVSUPPLY.
Turn the disconnect switch and the key start switch to the "ON" position.
Do not disconnect any of the machine harness connectors at this time.
In the machine harness connector for the Ambient Air Temperature sensor, measure the voltage between the contact for terminal A (wire A760-GY(Grey)) and the contact for terminal B (wire 235-BK(Black)) in the sensor connector. Expected Result:The voltage is 8.0 0.5 DCV. Results:
YES - The voltage is 8.0 0.5 DCV. The power supply is not the problem. Go