8M0000712 Mercury SEAL

Table 1
Diagnostic Codes Table    
Description    Conditions which Generate this Code    System Response    
91-08 Throttle Position Sensor : Abnormal Frequency, Pulse Width, or Period     The Electronic Control Module (ECM) has detected an invalid frequency.     The code is logged.
If equipped, the warning light will come on.
Engine RPM defaults to a predetermined safe speed.
The engine will remain at low idle.    The throttle switch provides the operator with the ability to select the desired engine speed. The throttle switch is a rotary switch with ten positions. The throttle switch is connected to the four switch inputs of the machine control module. A throttle command is sent to the engine's ECM from the machine control module. The throttle command is referred to as a duty cycle or as a Pulse Width Modulated (PWM) signal. The throttle command is valid when the following conditions exist:
The duty cycle is between 10 percent and 90 percent.
The PWM signal is 1.2 kHz 150 Hz.If the frequency of the throttle command is not correct or the duty cycle is not correct, a diagnostic code will be generated.When a diagnostic code is generated, the ECM ignores the throttle command and the desired engine speed is set to equal the current engine speed. When a problem is detected with the throttle signal, the throttle backup switch is enabled. The operator can use the throttle backup switch to set the desired engine speed. If the throttle backup switch is held in the ACCEL position, the desired engine speed will increase 200 rpm per second. If the throttle backup switch is held in the DECEL position, the engine speed will decrease 200 rpm per second.
Illustration 1 g01321814
Schematic for the throttle switch
Illustration 2 g01321820
A typical view of the P1 connector (wire side) pin locations. (P1-35) Digital return (P1-44) Throttle backup switch (P1-45) Throttle backup switch (P1-53) Throttle command
Illustration 3 g01345674
A typical view of the P2 connector (ECM side) pin locations.Test Step 1. Inspect the Electrical Connectors and the Wiring
Turn the keyswitch to the OFF position.
Illustration 4 g01325579
Typical engine ECM (1) J2 ECM connector (2) J1 ECM connector
Thoroughly inspect the J1/P1 ECM connector and the J2/P2 ECM connector. Inspect all of the connectors that are associated with the circuit.
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that is associated with the active diagnostic code.
Check the ECM connector (allen head screw) for the proper torque. Refer to the service Troubleshooting, "Electrical Connectors - Inspect".
Check the harness and wiring for abrasions and for pinch points from the sensors back to the ECM.Expected Result:All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.Results:
OK - The harness and wiring are OK. Proceed to Test Step 2.
Not OK - There is a problem in the connectors and/or wiring.Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.If applicable, use Caterpillar Electronic Technician (ET) to perform a wiggle test.STOPTest Step 2. Check for Active Diagnostic Codes
Connect Cat ET to the service tool connector.
Turn the keyswitch to the ON position.
Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.Note: Wait at least 30 seconds in order for the diagnostic codes to become active.Expected Result:No diagnostic codes are active.Results:
OK - No diagnostic codes are active.Repair: The problem may have been related to a faulty connection in the harness. Carefully reinspect the connectors and wiring. Refer to the service Troubleshooting, "Electrical Connectors - Inspect".STOP
Not OK - A 91-8 diagnostic code is active at this time. Proceed to Test Step 3.Test Step 3. Check the Throttle Signal on Cat ET
Turn the keyswitch to the ON position.
Observe the status of "Throttle" on Cat ET.
Turn the throttle switch and observe the status of "Throttle" and the switch inputs on Cat ET.
Turn the keyswitch to the OFF position.Expected Result:The status of the throttle switch changes, as the switch is operated.Results:
OK - The status of the throttle switch changes, as the switch is operated. The throttle and circuitry are operating correctly.Repair: If the problem is intermittent, refer to the service Troubleshooting, "Electrical Connectors - Inspect".STOP
Not OK - The status of the throttle switch does not change as the switch is operated. Proceed to Test Step 4.Test Step 4. Check the Throttle Command at the Machine Control Module
Turn the keyswitch to the ON position.
Use a multimeter to monitor the percent duty cycle of the throttle command at the machine control module. Adjust the throttle switch from the low idle position to the high idle position.
Turn the keyswitch to the OFF position.Expected Result:At low idle, the duty cycle is between 5 percent and 10 percent. At high idle, the duty cycle is between 90 percent and 95 percent.Results:
OK - The throttle command is correct. Proceed to Test Step 5.
Not OK - The throttle command is not correct. There may be a problem with the throttle switch or the machine control module.Repair: Refer to the System Operation Manual and the Testing and Adjusting Manual for the machine.STOPTest Step 5. Check the Throttle Command at the ECM
Turn the keyswitch to the OFF position.
Disconnect the J1/P1 ECM connector.
Remove the wire from ECM connector P1-53.
Reconnect the ECM connectors.
Turn the keyswitch to the ON position.
Use a multimeter to monitor the percent duty cycle of the throttle command between P1-53 (throttle command) and engine ground. Adjust the throttle switch from the low idle position to the high idle position.
Turn the keyswitch to the OFF position.
Replace all wires to the original configuration.Expected Result:At low idle, the duty cycle is between 5 percent and 10 percent. At high idle, the duty cycle is between 90 percent and 95 percent.Results:
OK - The throttle command is correct. The ECM is not processing the command properly. Verify that the ECM is receiving the correct battery voltage. If the ECM is receiving the