CM850 Electronic Control System – FAULT CODE 1242

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Overview

Accelerator Pedal Sensor SMALL | MEDIUM | LARGE

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 number 1 is twice as much as the signal voltage from accelerator position number 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.

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 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:

• Failed accelerator pedal position sensor 1 or failed accelerator pedal position sensor number 2.
• Accelerator pedal position sensor number 1 and accelerator pedal position sensor number 2 signal wires are shorted.

Refer to Troubleshooting Fault Code t05-1242