THERMOSTAT AS 3773044 - Caterpillar

Illustration 1 g06103636
Schematic for Engine Starting System
The ECM activates the intermediate start relay when the key switch is in the START position and the direction switch is in the NEUTRAL position. If a 168 code is present, the diagnostic code must be corrected before performing the following procedure "Check the key switch". See Troubleshooting, "Diagnostic Code List".After the Transmission ECM detects the system voltage at the START input, the ECM will activate the intermediate starter relay. All the following conditions need to be true for the software to energize the start relay:
Ignition Key in Start position
Starter Disconnect Switch is in the ON
The transmission in NEUTRAL position
Battery voltage is between 18 VDC and 32 VDC before the Start Relay is energized
Battery voltage is less than 32 VDC when the Start Relay is energized
Engine Speed is less than 400 RPMThe starter relays have system battery voltage on one side of the relay contacts. When the starter relays are energized by the intermediate start relay, system battery voltage is directed through the closed relay contacts. Next, the starter solenoids for the starter will energize. The starter solenoid contacts will close and +battery voltage will be applied to the starter to crank the engine for starting.Perform the following procedure if the engine will not crank with the key switch in the START position.Note: Refer to the engine service manual for your machine if the engine cranks but the engine is not starting.Verify that there are no active diagnostic codes for the intermediate starter relay. If a diagnostic code for the relay is active, troubleshoot the diagnostic code before attempting to start the engine.
Table 1
Troubleshooting Test Steps Values Results
1. Verify That The Machine Conditions Are Correct
A. Verify that the disconnect switch is in the ON position.
B. Verify that the parking brake is engaged.
C. Verify that the transmission is in NEUTRAL.
One or more of the listed machine conditions was not correct. YES: One or more of the listed machine conditions was not correct.
REPAIR: Ensure that all the listed machine conditions are correct. Then attempt to start the engine again.
STOP.
NO: All the listed machine conditions are correct. The engine will not crank and there are not any diagnostic codes for the intermediate starter relay.
Proceed to Test Step 2.
2. Check The Relays
A. The key switch is in the OFF position.
B. Obtain the aid of another technician. The other technician can place the key switch in the START position. Observe the starter relay. The relay should create an audible "click" when the key switch is first moved to the START position.
The relay is being energized. OK: The relay is being energized.
Proceed to Test Step 3.
NOT OK: The relay is not being energized.
REPAIR: There is a problem in the circuit for the starter relay. Refer to the Troubleshooting section of this manual. Find the problem in the relay circuit and repair the circuit.
3. Check The Condition Of The Batteries
A. The key switch is in the OFF position.
B. At the starter relays, measure the battery voltage from the contact that