0343188 JOHNSON PLATE, Frame, front

Table 1
Diagnostic Codes Table    
Code    Conditions which Generate this Code    System Response    
91-8 Throttle Position Sensor abnormal frequency, pulse width, or period     The Electronic Control Module (ECM) detects an incorrect duty cycle on the throttle signal. The duty cycle is less than 5 percent or the duty cycle is greater than 95 percent.
or
The throttle signal is greater than 1.228 kHz 150 Hz or less than 1.228 kHz 150 Hz.     The code is logged. The ECM flags the throttle position as invalid data. The desired engine speed is set to the last valid speed signal that was recognized by the ECM.    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 and four outputs. The throttle switch is connected to four inputs on the engine and hydraulic pump controller. The engine and hydraulic pump controller interprets the signals from the throttle switch as a throttle command. The engine and hydraulic pump controller then outputs a throttle signal to the engine's ECM. The throttle signal is referred to as a duty cycle or as a PWM signal. The throttle signal is valid when the following conditions exist:
The duty cycle is between 5 percent and 95 percent.
The PWM signal is 1.228 kHz 150 Hz.If the ECM detects an abnormal throttle signal, the ECM will generate a diagnostic code. If a diagnostic code is active for the throttle signal, the ECM ignores the throttle signal and the desired engine speed is set to the last valid speed that was recognized by the ECM. 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 140 rpm per second. If the throttle backup switch is held in the DECEL position, the engine speed will decrease 140 rpm per second.
Illustration 1 g01455543
Typical schematicTable 2 shows continuity between the contacts of the throttle position switch in each position.
Table 2
Throttle Position Switch    
Position     Contacts    
1     COM, S1    
2     COM, S1, S2    
3     COM, S2    
4     COM, S2, S3    
5     COM, S1, S2, S3    
6     COM, S1, S3    
7     COM, S3    
8     COM, S3, S4    
9     COM, S1, S3, S4    
10     COM, S1, S2, S3, S4    
Illustration 2 g01455539
P1 ECM connector (P1-15) Throttle backup switch (Accel) (P1-24) Throttle backup switch (Decel) (P1-29) Sensor common (P1-37) Throttle commandTest Step 1. Inspect Electrical Connectors and Wiring
Turn the keyswitch to the OFF position.
Illustration 3 g01139425
ECM (1) J1/P1 connectors (2) J2/P2 connectors
Thoroughly inspect the J1/P1 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 Troubleshooting, "Electrical Connectors - Inspect" for details.
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.STOPTest Step 2. Check for Active Diagnostic Codes
Connect Caterpillar Electronic Technician (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 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 through the full range of switch positions and observe the status of "Throttle" on Cat ET.
Turn the keyswitch to the OFF position.Expected Result:The throttle varies from 0 to 100 percent.Results:
OK - The throttle varies from 0 to 100 percent. The throttle and circuitry are operating correctly.Repair: If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".STOP
Not OK - The throttle signal did not vary from 0 to 100 percent. Proceed to Test Step 4.Test Step 4. Check the Throttle Command at the Engine and Hydraulic Pump Controller
Remove the wire C912-GN from terminal 30 of the engine and hydraulic pump controller.
Turn the keyswitch to the ON position.
Use a multimeter to monitor the percent duty cycle of the throttle command at terminal 30 of the engine and hydraulic pump controller. Adjust the throttle switch through the full range of switch positions.
Turn the keyswitch to the OFF position.
Return 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. Proceed to Test Step 5.
Not OK - The throttle command is not correct. There may be a problem with the throttle switch or the engine and hydraulic pump controller.Repair: If a problem is suspected with the throttle position switch, refer to Table 2 for information on continuity between the switch contacts when the switch is in each