28656 Mercury NUT

Illustration 1 g00666827
Schematic
Table 1
Correlation Between Throttle Switch Position and Status of the Throttle Inputs    
Throttle Switch Position    Desired Engine Speed    Status on ET    
"Throttle Input #1" "Throttle Input #2"    "Throttle Input #3"    "Throttle Input #4"    
1     700     On     Off     Off     Off    
2     840     On     On     Off     Off    
3     980     Off     On     Off     Off    
4     1120     Off     On     On     Off    
5     1260     On     On     On     Off    
6     1400     On     Off     On     Off    
7     1540     Off     Off     On     Off    
8     1680     Off     Off     On     On    
9     1800     On     Off     On     On    
10     1880     On     On     On     On    Test Step 1. Inspect Electrical Connectors and Wiring
Turn the keyswitch to the OFF/RESET position.
Thoroughly inspect ECM connector J1/P1, machine connector J3/P3, and throttle switch connector J118/P118. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Check the harness and wiring for corrosion, abrasion, and pinch points from the throttle switch to the ECM.Expected Result:All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, of abrasions, and of pinch points.Results:
OK - Proceed to Test Step 2.
Not OK - Repair: Repair the circuit.Verify that the repair eliminates the problem. Stop.Test Step 2. Check "Throttle Cab Switch Position" on the Caterpillar Electronic Technician (Cat ET)
Connect Cat ET to the data link connector.
Turn the keyswitch to the ON position.
Observe the status of the throttle switch and the throttle inputs on Cat ET while you operate the throttle switch in each position.Expected Result:The status screen on Cat ET corresponds with the information in Table 1.Results:
OK - The throttle switch is functioning properly at this time.Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent. Stop.
Not OK - Record the suspect input. Proceed to Test Step 3.Test Step 3. Jumper the Switch Input at the Throttle Switch Connector
Disconnect J118/P118Throttle Switch connector.
Observe the status of the suspect throttle input on Cat ET.
Use a suitable piece of wire to short P118:1 (Digital Return) to the terminal for the suspect throttle input at P118Throttle Switch connector.
Observe the status of the suspect throttle input on Cat ET.
Remove the wire short.Expected Result:The status of the suspect throttle input is "Off" when J118/P118Throttle Switch connector is disconnected. The status is "On" when the wire short is installed.Results:
OK - The harness and the ECM are OK.Repair: Replace the throttle switch.Verify that the repair eliminates the problem. Stop.
Not OK - Proceed to Test Step 4.Test Step 4. Check for Shorts in the Harness
Turn the keyswitch to the OFF/RESET position.
Disconnect ECM connector J1/P1 and J118/P118Throttle Switch connector.
Measure the resistance between engine ground and the terminal for the suspect throttle input at P118 Throttle Switch connector.
Measure the resistance between the terminal for the suspect throttle input at P118 Throttle Switch connector and the remaining terminals at the connector.Expected Result:Resistance is greater than 20,000 for each reading.Results:
OK - Proceed to Test Step 5.
Not OK - There is a short in the harness between the ECM and the throttle switch.Repair: Repair the circuit.Verify that the repair eliminates the problem. Stop.Test Step 5. Check Resistance through the Harness
Illustration 2 g00666871
ECM connector P1 (ECM side)
Use a suitable piece of wire to short P118:1 (Digital Return) to the terminal of the suspect throttle input at P118throttle switch connector.
Measure the resistance between P1:29 (Digital Return) and the terminal for the suspect throttle input at ECM connector P1.Expected Result:Resistance is less than 10 Ohms.Results:
OK -