819946A 3 Force PISTON KIT (15)

Table 1
Diagnostic Trouble Codes    
CDL Code     Code Description     Comments    
91-2     Throttle Position Sensor : Erratic, Intermittent, or Incorrect     There is an invalid combination of positions for the multi-position switches.
The code is logged. The Electronic Control Module (ECM) uses a default value of zero percent. The engine speed is limited to low idle.    The throttle switch provides the operator with the ability to select the engine speed to low idle or high idle. The throttle switch also allows the engine speed to be set at a maximum operating speed.The throttle switch is connected to the four throttle inputs of the ECM. Each position generates a specific on/off pattern on the throttle inputs. A diagnostic code is generated if a pattern that does not correspond with any of the switch positions is detected.Once a diagnostic code is generated, the ECM ignores the throttle input signals and the desired engine speed defaults to a predetermined speed. Although, if the actual engine speed is below the predetermined speed, the desired engine speed is set to the current engine speed. The desired engine speed is set to low idle if the engine is not running.The electronic service tool can be used to view the status of the inputs for the throttle switch.
Illustration 1 g02174337
Schematic for the throttle switch
Illustration 2 g02168540
P1 ECM connector (5) Throttle return (56) Throttle switch (high idle parity) (47) Throttle switch (high idle) (23) Throttle switch (low idle parity) (22) Throttle switch (low idle)
Illustration 3 g01250541
Terminal locations at the throttle switch (Terminal 1) Throttle switch (low idle) (Terminal 2) Throttle return (Terminal 3) Throttle switch (high idle parity) (Terminal 4) Throttle switch (low idle parity) (Terminal 5) Throttle return (Terminal 6) Throttle switch (high idle)Test Step 1. Check the Status of the Throttle Inputs
Turn the keyswitch to the OFF position.
Establish communication between Caterpillar Electronic Technician (ET) and the ECM. Refer to Troubleshooting, "Electronic Service Tools", if necessary.
Turn the keyswitch to the ON position.
Observe the status of the throttle switch and the throttle inputs on Cat ET while you operate the throttle switch in each position.Results:
The throttle switch is functioning correctly at this time. - Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the fault is intermittent.STOP
The throttle switch is not functioning correctly at this time. Record the suspect input. - Proceed to Test Step 2.Test Step 2. Jumper the Switch Input at the Throttle Switch Connector
Turn the keyswitch to the OFF position.
Disconnect the throttle switch connector.
Turn the keyswitch to the ON position.
Observe the status of the suspect throttle input on Cat ET.
Use a suitable jumper wire to short the terminal for the suspect throttle input at the throttle switch connector to engine ground.
Observe the status of the suspect throttle input on Cat ET.
Remove the jumper wire.Results:
The status of the suspect throttle input is OFF when the throttle switch connector is disconnected. The status is ON when the jumper wire is installed. - The status is correct. The harness and the ECM are OK.Repair: Replace the throttle switch.Use Cat ET to clear all logged diagnostic codes and then verify that the repair eliminates the fault.STOP
The status of the suspect throttle input is not OFF when the throttle switch connector is disconnected. The status is not ON when the jumper wire is installed. - The status is not correct. Verify that the return circuit for the throttle switch is continuous to engine ground. Ensure that the return circuit has a good connection to engine ground. Proceed to Test Step 3.Test Step 3. Check the Harness and the ECM
Turn the keyswitch to the OFF position.
Disconnect the J1/P1 ECM connector and remove the wire for the suspect throttle input.
Reconnect the connectors.
Turn the keyswitch to the ON position.
Observe the status of the suspect throttle input on Cat ET.
Use a jumper wire to short the terminal for the suspect throttle input to engine ground.
Observe the status of the suspect throttle input on Cat ET.
Turn the keyswitch to the OFF position.
Remove the jumper wire from the J1/P1 ECM connector and reconnect all wires and connectors.Results:
The status of the suspect throttle input is OFF when the throttle input is open. The status is ON when the jumper wire is installed. - The status is correct. There is a fault in the harness between the ECM and the throttle switch.Repair: Repair the circuit.Use Cat ET to clear all logged diagnostic codes and then verify that the repair eliminates the fault.STOP
The status of the suspect throttle input is not OFF when the throttle input is open. The status is not ON when the jumper wire is installed. - The status is not correct. The switch signal appears at the ECM. The ECM is not reading the switch correctly.Repair: The ECM is not responding to the switch inputs. There is a problem with the ECM. Refer to Troubleshooting, "ECM - Replace" before you replace the ECM.STOP