3176C, 3406E and 3456 Industrial Engines Troubleshooting – Speed Control – Test

System Operation Description:

Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle position sensor or if the diagnostic code in Table 1 is active or easily repeated.

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 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 g01429530
Schematic for the throttle position sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

 

  1. Remove electrical power from the ECM.


Illustration 2 g01139425
ECM

(1) J1/P1 connectors

(2) J2/P2 connectors

Thoroughly inspect the J1/P1 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 g01429547
P1 ECM connector

(P1-6) +Battery

(P1-37) Throttle position


Illustration 4 g01159881
Connector for the throttle position sensor

(A) +Battery

(B) Return

(C) Throttle position

  1. Perform a 45 N (10 lb) pull test on each of the wires in the circuit.

 

  1. Check the allen head screw from each ECM connector for the proper torque. Refer to Troubleshooting, “Electrical Connectors – Inspect” for the correct torque value.

 

  1. 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.

    STOP

Test Step 2. Check the Status for “Throttle Position”

 

  1. Connect Caterpillar Electronic Technician (ET) to the service tool connector.

 

  1. Restore electrical power to the ECM.

 

  1. Observe the status for “Throttle Position” on Cat ET while you operate the throttle control through the entire range of travel.

Expected Result:

The status is zero percent when the throttle control is fully deactivated. The status progressively increases to 100 percent when the throttle control 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 – The throttle control that is displayed on Cat ET does not correspond to the movement of the throttle control. Proceed to Test Step 3.

Test Step 3. Check the Supply Voltage at the Sensor

 

  1. Remove electrical power from the ECM.

 

  1. Disconnect the connector for the throttle position sensor.

 

  1. Restore electrical power to the ECM.

 

  1. Measure the voltage across terminal A (+Battery) and terminal B (Return) on the harness side of the connector.

 

  1. Remove electrical power from the ECM.

Expected Result:

The supply voltage is at least 11 VDC for a 12 volt system. The supply voltage is at least 22 VDC for a 24 volt system.

Results:

 

  • OK – The correct voltage is measured at the sensor connector. The sensor is receiving the correct supply voltage. Proceed to Test Step 4. 
  • Not OK – The voltage is not correct at the sensor connector. The sensor is not receiving the correct supply voltage. Proceed to Test Step 6.

Test Step 4. Check the Duty Cycle at the Sensor

 

  1. Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the connector for the throttle position sensor.

 

  1. 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.

 

  1. Restore electrical power to the ECM.

 

  1. Measure the duty cycle between terminal B (digital return) and terminal C (throttle position) at the 7X-6370 Adapter Cable As (3-PIN BREAKOUT) while you operate the throttle control .

 

  1. Remove electrical power from the ECM.

 

  1. Remove the breakout harness. Restore the wires to the original configuration.

Expected Result:

The duty cycle is between 5 and 95 percent.

Results:

 

  • OK – The duty cycle is within specifications for the entire range of the throttle control. The sensor is producing a valid signal. Proceed to Test Step 5. 
  • Not OK – The duty cycle is not within specifications.Repair: The sensor is not producing a valid signal. Replace the throttle position sensor. Verify that the repair eliminates the problem.

    STOP

Test Step 5. Check the Duty Cycle at the ECM

 

  1. Remove the throttle signal wire from ECM connector P1-37.

 

  1. Restore electrical power to the ECM.

 

  1. Measure the duty cycle of the sensor. Measure the duty cycle between wire P1-37 and -Battery while you operate the throttle control .

 

  1. Remove electrical power from the ECM.

Expected Result:

The duty cycle is between 5 and 95 percent.

Results:

 

  • OK – The duty cycle is within specifications for the entire range of the throttle control .Repair: A valid signal appears at the ECM, but the ECM is not reading the signal properly. Replace the ECM. Refer to Troubleshooting, “ECM – Replace” for complete instructions. Verify that the repair eliminates the problem.

    STOP

     

  • Not OK – The frequency and the duty cycle are not within specifications.Repair: There is not a valid signal at the ECM connector. Repair the signal wire in the harness. Verify that the repair eliminates the problem.

    STOP

Test Step 6. Check the Supply Voltage at the ECM

 

  1. Disconnect the J1/P1 ECM connector.

 

  1. Remove the supply wire from terminal P1-6. Install a jumper wire into the terminal location for the supply wire.

 

  1. Reconnect the J1/P1 ECM connector.

 

  1. Restore electrical power to the ECM.

 

  1. Measure the voltage between the wire jumper in terminal P1-6 and -Battery .

 

  1. Remove electrical power from the ECM.

Expected Result:

The supply voltage is at least 11 VDC for a 12 volt system. The supply voltage is at least 22 VDC for a 24 volt system.

Results:

 

  • OK – The correct voltage is measured at the ECM.Repair: There is a problem in the harness between the ECM and the sensor. Repair the harness or replace the harness. Verify that the repair eliminates the problem.

    STOP

     

  • Not OK – The voltage is not correct at the ECM.Repair: The ECM does not appear to be producing the correct supply voltage. Replace the ECM. Refer to Troubleshooting, “ECM – Replace” for complete instructions. Verify that the repair eliminates the problem.

    STOP

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