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SPN 91 - FMI 2 (Fault Code 1242)

SPN91 FMI2 (Accelerator Pedal or Lever Position Sensor 1 and 2 - Data Erratic, Intermittent, or Incorrect)
Fault Code 1242
ISB, ISC, and ISL with CM2150 - Accelerator Pedal Sensor

CODES:
Fault Code: 1242
PID(P), SID(S): P091
SPN: 91
FMI: 2/2
Lamp: RED
SRT:

REASON: Accelerator Pedal or Lever Position Sensor 1 and 2 - Data Erratic, Intermittent, or Incorrect. Accelerator position sensor number 1 and number 2 are reading different values.

EFFECT: The engine will only idle.

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 electronic 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 accelerator position 2.

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 readings between accelerator position sensor 1 and accelerator position sensor 2 differ by more than 2 percent.

Action Taken When the Fault Code is Active:
• The ECM illuminates the red STOP ENGINE light immediately when the diagnostic runs and fails.

Conditions for Clearing the Fault Code:
The ECM will turn off the red STOP ENGINE light immediately after the diagnostic runs and passes.

Shop Talk:
Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

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 should be installed.

This fault code becomes active when the accelerator position sensor number 1 and accelerator position sensor number 2 are not reading the same value.

Possible causes of the fault include:
• Damaged accelerator pedal position sensor number 1 or damaged accelerator pedal position sensor number 2.
• Damaged accelerator pedal position sensor number 1 and damaged accelerator pedal position sensor number 2 signal wires are shorted together.


Read More:
SPN 2623 - FMI 4 (Fault Code 1241)
SPN 2623 - FMI 3 (Fault Code 1239)









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