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Cummins ISB4.5 CM2150 Fault Code: 1239 PID: SPN: 2623 FMI: 3 Accelerator Pedal or Lever Position Sensor 2 Circuit – Voltage Above Normal or Shorted to High Source.

Circuit Description
The accelerator position sensor is a Hall effect sensor attached to the accelerator pedal. The accelerator position sensor varies the signal voltage to the engine control module (ECM) as the accelerator pedal is depressed and released. Low signal voltage is received by the ECM when the accelerator pedal is at 0 percent. A high signal voltage is received by the ECM when the accelerator pedal is at 100 percent. The accelerator pedal position circuit contains an accelerator pedal position 5-volt supply, accelerator pedal position return, and accelerator pedal position signal.

The accelerator pedal contains two position sensors. These position sensors are used to measure the throttle position. Both position sensors receive a 5-volt supply from the ECM. A corresponding signal voltage based on the position of the accelerator pedal is then received from the ECM. The signal voltage for accelerator position 1 is twice as much as the signal voltage from the accelerator position 2.

When the ECM senses a signal voltage lower than the normal operating range of the sensor, this fault code is set.

Component Location
The accelerator pedal position sensor is located on the accelerator pedal. Refer to the original equipment manufacturer (OEM) troubleshooting and repair manual.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the keyswitch is in the ON position.

Conditions for Setting the Fault Codes
The ECM detects that the throttle pedal signal voltage is greater than a calibratible value for more than 1 second.

Action Taken When the Fault Code is Active
-The ECM illuminates the amber CHECK ENGINE light and/or the malfunction indicator lamp (MIL) immediately when the diagnostic runs and fails.

Conditions for Clearing the Fault Code
-To validate the repair, start the engine and let it idle for 1 minute.
-The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.
-The ECM will turn off the malfunction indicator lamp (MIL) after three consecutive ignition cycles that the diagnostic runs and passes.
-This fault code and malfunction indicator lamp (MIL) can also be cleared with INSITE™ electronic service tool.

Shop Talk
Newer engines use two throttle position sensors to determine the throttle position. Older throttle pedals used a single throttle position sensor and an idle validation switch. If Fault Codes 132 and 1241 are active when the accelerator pedal is in the idle position and Fault Code 132 goes inactive and Fault Code 1239 goes active when the throttle is depressed, the incorrect throttle pedal has been installed in the vehicle. A throttle pedal with two acceleration position sensors must be installed.

If troubleshooting an intermittent accelerator problem, the accelerator pedal position sensor 2 signal voltage can be monitored with INSITE™ electronic service tool, while flexing the harness to locate the intermittent connection.

Possible Causes
-Accelerator pedal position 2 signal circuit shorted to battery or 5-VDC supply
-Open accelerator pedal return circuit in the harness or connections
-Accelerator supply shorted to battery
-Damaged accelerator pedal position sensor.

*The three wires in the accelerator position sensor circuit must be twisted together.