0777172 JOHNSON Primer

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 duty cycle on the throttle signal. The duty cycle is less than 40 percent or the duty cycle is greater than 61 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 pedal assembly that allows the operator to control the speed of the engine. The geometry of the pedal assembly 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 Pulse Width Modulated PWM signal that varies with the position of the throttle pedal. The throttle position sensor produces a minimum duty cycle in the released position and a maximum duty cycle in the fully depressed position. When the pedal is released, the ECM translates the sensor's output signal to a throttle position of 0 percent. When the pedal is fully depressed, the ECM translates the output signal to a throttle position of 100 percent.The throttle position sensor is powered by 8.0 0.4 VDC that is provided by the ECM. A digital return for the sensor is also provided by the ECM.The ECM uses an automatic calibration function that allows the ECM to minimize the deadband of the sensor. The automatic calibration function assumes a range of PWM duty cycle at powerup. If the duty cycle of the sensor exceeds this initial range, the automatic calibration function adjusts the limits of the duty cycle in order to adjust for the new range.
Illustration 1 g01395896
Schematic for the throttle position sensorTest Step 1. Inspect the Electrical Connectors and the Wiring
Remove electrical power from the ECM.
Illustration 2 g01139425
ECM (1) J1/P1 connectors (2) J2/P2 connectors
Thoroughly inspect the J1/P1 ECM connector and the J2/P2 ECM connector. Inspect all of the connectors that are associated with the circuit.Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 3 g01824035
P1 ECM connector (P1-35) + 8 V digital supply (P1-29) Digital return
Illustration 4 g01891575
P2 ECM connector (P2-24) Throttle position
Illustration 5 g01159881
Connector for the throttle position sensor (A) +8 V 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 from each ECM connector 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. Inspect the Throttle Pedal Assembly
Inspect the throttle pedal assembly for components that are loose, bent, missing, or worn.
Slowly depress the pedal and release the pedal.Expected Result:The throttle pedal assembly operates smoothly without excessive drag. The pedal springs back smoothly to the low idle position without assistance.Results:
OK - The throttle pedal assembly functions properly. Proceed to Test Step 3.
Not OK - The throttle pedal assembly is in poor repair.Repair: Repair the throttle pedal assembly or replace the throttle pedal assembly, as required.STOPTest Step 3. Check the Status for "Throttle Position"
Connect Caterpillar Electronic Technician (ET) to the service tool connector.
Restore electrical power to the ECM.
Observe the status for "Throttle Position" on Cat ET while you operate the throttle pedal through the entire range of travel.Expected Result:The status is zero percent when the throttle pedal is released. The status progressively increases to 100 percent when the throttle pedal is fully depressed.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 - The throttle position that is displayed on Cat ET does not correspond to the movement of the throttle pedal. Proceed to Test Step 4.Test Step 4. Check the Supply Voltage at the Sensor
Remove electrical power from the ECM.
Disconnect the connector for the throttle position sensor.
Restore electrical power to the ECM.
Measure the voltage across terminal A (+8 V supply) and terminal B (digital return) on the harness side of the connector.
Remove electrical power from the ECM.Expected Result:The supply voltage measures 8.0 0.4 VDC at the sensor connector.Results:
OK - The correct voltage is measured at the sensor connector. The sensor is receiving the correct supply voltage. Proceed to Test Step 5.
Not OK - The voltage is not correct at the sensor connector. The sensor is not receiving the correct supply voltage. Proceed to Test Step 7.Test Step 5. Check the Duty Cycle at the Sensor
Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the connector for the throttle position sensor.
Remove the signal wire from terminal C of the connector for the throttle position sensor. Remove the wire from the harness side of the connector.
Restore electrical power to the ECM.
Measure the duty cycle