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PTO Throttle Signal Invalid (Diagnostic Code: SPN 644 - FMI 8)

SPN644 FMI8
0030-08 PTO Throttle Signal Invalid (29)

Figure 1.1 - SPN 644 FMI 8 (Murphy PowerView)


PID 0030 FMI 08

Conditions Which Generate This Code:
The Engine Control Module (ECM) detects the following conditions:
  • The "PTO Configuration" is programmed to "Remote Throttle".
  • The ECM is not receiving a valid signal from the PTO throttle.
  • The ECM has been powered for at least three seconds.
Note: If the "PTO Configuration" is programmed to "Remote Throttle", the ECM must receive a proper signal from the remote throttle at all times. The remote throttle signal must be present even when the PTO ON/OFF switch is in the OFF position.

System Response:
The ECM returns the engine to low idle when the problem is detected. "DIAG" will be displayed next to the status for "Throttle Position" on Caterpillar Electronic Technician (ET).

Possible Performance Effect:
The engine will remain at low idle while the diagnostic code is active.

Troubleshooting:
Perform the following diagnostic procedure:
"Remote PTO Accelerator Position Sensor Circuit - Test"
Use this procedure if any of the following diagnostic codes are indicated:
  • 30-08 PTO Throttle signal invalid (29)
  • 30-13 PTO Throttle out of calibration (29)
Also, use this procedure if the remote accelerator position sensor is suspected of improper operation.

Remote Accelerator Position Sensor
A remote accelerator position sensor may be used for PTO purposes. The remote accelerator position sensor should be connected to terminal J1/P1-68 of the Engine Control Module (ECM). Before the ECM will respond to the remote accelerator position sensor, the ECM "PTO Configuration" must be programmed to "Remote Throttle", and the "PTO On/Off Switch" must be in the ON position.

Read More:
PTO Configurations for On-Highway Truck (Caterpillar Engines)

The remote accelerator position sensor must be powered from the vehicle battery (+12 V). A +12 V version of the accelerator position sensor must be used for the remote accelerator position sensor, and the +8 V version for the accelerator pedal position sensor must be used in the cab.

The ECM will not respond to the remote accelerator position sensor while 253-02 diagnostic code is active.

The remote accelerator position sensor provides a throttle position signal to the ECM. The output of the remote accelerator position sensor is a constant frequency signal with a pulse width that varies with the position of the sensor. This output signal is referred to as either a duty cycle or a pulse width modulated signal (PWM).

The output signal of the remote accelerator position sensor is expressed as a percentage between 3 and 100 percent. The accelerator position sensor will produce a duty cycle of 10 to 22 percent at low idle and 75 to 90 percent when the sensor is fully actuated. The percent of duty cycle is translated in the ECM into a throttle position of 3 to 100 percent.

If the vehicle is using the ECM dedicated PTO functions, the accelerator position sensor will be ignored while the engine is in "PTO Mode" and the "PTO Configuration" is programmed to the "Remote Throttle" option.

The ECM is in "PTO Mode" while the PTO on/off switch is on. This can be checked through the status screen on Caterpillar Electronic Technician (ET).

The ECM will not respond to the remote accelerator position sensor when both of the following conditions are met:
  • The PTO on/off circuit is switched from the OFF position to the ON position.
  • The ECM reads the remote accelerator position sensor above low idle.
This prevents the engine from experiencing unexpected acceleration or sudden acceleration when the PTO on/off circuit is turned on. The remote accelerator position sensor must return to low idle before the ECM will respond. The ECM must also see a transition from the OFF position to the ON position in the PTO on/off switch in order to allow the other PTO speed control functions to operate. If the engine is started with the PTO on/off switch in the ON position, the accelerator will respond. The response will occur only if the accelerator pedal is first returned to the low idle position. The other engine speed controls will not respond.
Typical schematic for remote accelerator pedal position sensor
Pin locations on ECM connector: J1/P1
(P1-3) Input sensor common #2
(P1-5) AP sensor/switch sensor common
(P1-68) Input #8 (remote accelerator position sensor)

Test Step 1. Inspect the Electrical Connectors and the Wiring
A. Connect Cat ET to the data link connector. Turn the ignition key switch to the ON position. Verify that the parameter for the PTO configuration is programmed to the "Remote Throttle".
Figure 1.2 - PTO Configuration
B. Turn the ignition key switch to the OFF position.
C. Thoroughly inspect ECM vehicle harness connector J1/P1, the firewall bulkhead connector and the connector for the remote accelerator position sensor.
D. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the remote accelerator position sensor.
E. Check the allen head screw on each ECM connector for the proper torque.
F. Check the harness and wiring for abrasion and pinch points from the remote accelerator position sensor to the ECM.
Expected Result: All connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion or of pinch points.
If Not OK: 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.

Test Step 2. Check for Active Diagnostic Codes
A. Ensure that Cat ET is connected to the data link connector.
B. Turn the ignition key switch to the ON position.
C. Monitor the active diagnostic code screen on Cat ET. Check and record active diagnostic codes.
Read More: How to Connecting Caterpillar ET Software to the ECM.
Result: There are no active diagnostic codes that are related to the remote accelerator position sensor at this time, but a problem is suspected (intermittent).
Figure 1.3 - Logged Diagnostic Codes

Test Step 3. Check the Supply Voltage for the Remote Accelerator Position Sensor
A. Verify that the ignition key switch is in the ON position.
B. Measure the voltage between terminal "A" (+12 V) and terminal "B" (sensor common) at J406 remote accelerator position sensor connector.
Expected Result: The measured voltage is between 11.0 VDC and 13.5 VDC.
If Not OK: Not OK - The vehicle wiring or the battery is causing the problem. Repair the wiring or the battery. Replace the wiring or the battery. Perform the repair that is necessary. Verify that the repair has fixed the problem.

Test Step 4. Check the Duty Cycle of the Remote Accelerator Pedal Position Sensor
A. Verify that the ignition key switch is in the ON position.
B. Monitor the duty cycle of the PTO throttle sensor on Cat ET. Access the following display screen in order:
"Service" - "Calibrations" - "Monitor Throttle Position Sensor"
Expected Result: The duty cycle is between 10 and 22 percent with the accelerator pedal assembly in the low idle position, and the duty cycle is between 75 and 90 percent with the accelerator pedal assembly in the high idle position.
If Not OK: The remote accelerator position sensor is not operating correctly. Proceed to Test Step 5.

Test Step 5. Check the Duty Cycle of the Remote Accelerator Position Sensor at the Sensor
A. Turn the ignition key switch to the OFF position.
B. Remove terminal J406-C (throttle position signal) from the connector for the remote accelerator position sensor.
C. Connect the multimeter probes to terminal "C" (throttle position signal) and terminal "B" (sensor common)
D. Turn the ignition key switch to the ON position.
E. While the duty cycle is being monitored on the multimeter, actuate the remote accelerator position sensor.
Expected Result: The duty cycle is between 10 and 22 percent with the remote accelerator position sensor in the low idle position, and the duty cycle is between 75 and 90 percent with the remote accelerator position sensor in the high idle position.
If Not OK: The sensor or the accelerator control is faulty. Replace with CAT P/N: 134-0670


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