PISTON 3G9883 - Caterpillar

Illustration 1 g00648821
Schematic Of The Inlet Air Temperature SenderNote: Ensure that the desired diagnostic code (CID FMI) is on hold. Ensure that the "SERV CODE" indicator is ON. Use the electrical system schematic for the engine that is being serviced to find the connector contact on the Main Display Module which corresponds to the CID that is currently shown.This diagnostic code is recorded when the Main Display Module reads the voltage of the signal as being too low. The following examples are possible causes.
The inlet air temperature sender unit has a problem.
The signal circuit for the inlet air temperature sender unit in the engine harness is shorted to ground.
The Main Display Module has a problem.Note: The Main Display Module is unable to determine when a sender or sender signal harness is open or the resistance is too high.
Measure the Resistance of the Sender.
Turn the "ECS" to the OFF/RESET position.
Disconnect the engine harness from the inlet air temperature sender unit.
Measure the resistance that is between the two contacts of the sender connector. The following table illustrates the correct approximate resistance at various temperatures.
Table 1
Approximate Resistances For The Sender Connector Contacts    
Temperature     Resistance    
25 2°C (77 3.6°F)     1000 Ohms    
100 2°C (212 3.6°F)     103.7 Ohms    
Check the Display Area and the Harness.
Turn the "ECS" switch to the OFF/RESET position.
Check for loose connections or for corroded connections to the inlet air temperature sender.
Replace the corroded contacts and tighten the loose connections.
Turn the "ECS" to the COOLDOWN/STOP position. The "SERV CODE" indicator should be ON for the diagnostic code CID 172 FMI 04.
Disconnect the engine harness from the inlet air temperature sender unit. Observe the "SERV CODE" indicator.Expected Result: The "SERV CODE" indicator should turn OFF.Results:
OK - The "SERV CODE" indicator turns OFF. The inlet air temperature sender unit has a problem. Replace the inlet air temperature sender unit.
Not OK - The SERV CODE indicator stays ON. The harness wiring or the Main Display Module has a problem. Proceed to Step 3.
Check the Sender Wire for a Short to Ground.
Turn the "ECS" to the OFF/RESET position.
Disconnect the engine harness from the inlet air temperature sender unit.
Disconnect the harness from the main display module.
At the harness connector for the main display module, measure the resistance from contact 28 to contact 2 and frame ground.Expected Result: The resistance should be greater than 5000 Ohms.Results:
OK - The resistance is greater than 5000 Ohms. The wiring is correct. It is unlikely tht the main display module is the problem. Exit this procedure and begin this procedure again at Step 1. If the cause of the diagnostic fault is not found, replace the Main Display Module.
Not OK - The resistance is less than 5000 Ohms. The harness wiring has a problem. There is a short to ground in the inlet air temperature sender wire. Repair the harness or replace the harness. STOP.