ENGINE AR- 20R1808 - Caterpillar

Illustration 1 g01066105
Schematic for Magnetic Switches for the Start RelaysThis diagnostic code is recorded when the power train electronic control module (ECM) indicates that the current is below normal for the start relays (open circuit).Note: Ensure that the diagnostic code for the start relays is active. Before performing this procedure, refer to table 1 in order to determine the connector contact number and the wire number that corresponds to the failed circuit.
Table 1
Information for Starter Relays    
Fault    Connector Contact Number    Wire Number    
Starter Relays     J1-8 (1)     306-GN    
( 1 ) This is the connector contact number of the power train ECM.Note: All return lines for the start relays are joined. All return lines connect to contacts J1-7 and J2-3 (wire 975-WH) of the power train ECM.Note: The approximate coil resistance of each start relay is 15 to 65 Ohms.Possible causes of this diagnostic code are listed:
There is a harness fault.
A solenoid is disconnected or there is an open circuit.System Response:The machine response is listed:
The engine will not start.Test Step 1. CHECK THE RESISTANCE OF THE START RELAYS.
Turn the key start switch and the disconnect switch to the OFF position.
Disconnect the machine harness from both start relays at connectors M-C17 and M-C18.
Choose one start relay. Measure the resistance between the two contacts of the connector of the start relay. Measure the resistance between the two contacts of the connector of the second start relay.Expected Result:The resistance for each start relay should be between 15 - 65 ohms.Results:
YES - The resistance of each start relay is correct. The signal wire for a start relay or the return wire for a start relay (wire 975-WH) is open in the harness. Reconnect the start relays. Proceed to Test Step 2.
NO - This start relay is failed.Repair: Replace the start relay. Stop.Test Step 2. CHECK THE CIRCUIT FOR THE START RELAYS FOR AN OPEN.
The key start switch and the disconnect switch remain in the OFF position.
Disconnect the machine harness connectors J1 and J2 from the power train ECM.
Connect one start relay to the machine harness. The second start relay remains disconnected.
At machine harness connector J1 or J2, measure the resistance from the signal contact for the start relay J1-8 to J2-3 (return) or J1-7 (return). Refer to table 1.
Disconnect the first start relay. Connect the second start relay to the machine harness.
At machine harness connector J1 or J2, again measure the resistance from the signal contact for the start relay J1-8 to J2-3 (return) or J1-7 (return). Refer to table 1. Expected Result:Each resistance should be between 15 - 65 ohms.Results:
YES - The circuit resistances for the machine harness are correct. Suspect an intermittent fault. Proceed to Test Step 3.
NO - Resistance is not correct. The open is in the signal wire for a start relay or in wire 975-WH of the machine harness. Check continuity on each of the circuits.Repair: Repair the machine harness or replace the machine harness. Stop.Test Step 3. CHECK IF THE FAULT