0387239 JOHNSON SPARK PLUG, Ch qul-77v, 140

Table 1
Diagnostic Codes Table
Code and Description 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 frequency on the throttle signal or an incorrect duty cycle on the throttle signal. The frequency is below 150 Hz or the frequency in above 1000 Hz. The duty cycle is less than 5 percent or the duty cycle is greater than 95 percent. The code is logged. The ECM flags the throttle position as invalid data and a default value of zero percent is used. The engine speed is limited to low idle. The throttle position sensor provides the throttle signal to the ECM. The throttle position sensor is mounted to a mechanism that allows the operator to control the speed of the engine. The geometry of the mechanism controls both the travel of the sensor and the range of the output signal. The throttle position sensor cannot be adjusted.The output from the throttle position sensor is a PWM signal that varies with the position of the mechanism. The throttle position sensor produces a minimum duty cycle in the deactivated position and a maximum duty cycle in the fully activated position. When the throttle is deactivated, the ECM translates the sensor's output signal to a throttle position of 0 percent. When the throttle is fully activated, the ECM translates the output signal to a throttle position of 100 percent.
Illustration 1 g01421694
Schematic for the throttle position sensor
The connection of any electrical equipment and the disconnection of any electrical equipment may cause an explosion hazard which may result in injury or death. Do not connect any electrical equipment or disconnect any electrical equipment in an explosive atmosphere.
Test Step 1. Inspect the Electrical Connectors and the Wiring
Remove the electrical power from the ECM.
Illustration 2 g01388291
Locations of the connectors for the speed control (left side engine view)
(1) J1/P1 ECM connectors
Illustration 3 g01123466
Electronic throttle mechanism
Illustration 4 g01122049
Throttle lever mechanism
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Throttle knob mechanism
Thoroughly inspect connector (1). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 6 g01382651
P1 ECM connector
(P1-5) Digital return
(P1-66) Throttle position
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Terminals at the customer connector that are associated with the throttle position sensor circuit
(9) Digital return
(10) Throttle position
Illustration 8 g01159881
Terminal locations at the connector for the throttle position sensor
(A) Supply
(B) Digital return
(C) Throttle position
Perform a 45 N (10 lb) pull test on each of the wires in the circuit.
Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value.
Check the harness and the wiring for abrasion and for pinch points. Expected Result:All of the connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion and of pinch points.Results:
OK - The harness and connectors appear to be OK. Proceed to Test Step 2.
Not OK - The connectors and/or wiring are not OK.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 the Status for "Throttle Position"
Connect Caterpillar Electronic Technician (ET) to the service tool connector.
Restore the electrical power to the ECM.
Observe the status for "Throttle Position" on Cat ET while you operate the throttle mechanism through the entire range of travel. Expected Result:The status is zero percent when the throttle mechanism is fully deactivated. The status progressively increases to 100 percent when the throttle mechanism is fully activated.Results:
OK - The throttle position sensor is working properly.Repair: There may be an intermittent electrical problem with the harness or the connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.STOP
Not OK -