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Home >> Mitsubishi >> 2003 >> Montero XLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P2121: Accelerator Pedal Position Sensor (Main) Circuit Range/Performance Problem >> Diagnostic Procedure
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Diagnostic Procedure

CAUTION: To prevent damage to scan tool (MB991502), always turn the ignition off before connecting or disconnecting it.
  1. Check connector D-138 at accelerator pedal position sensor and accelerator pedal position switch for damage. If the connector is in good condition, go to the next step, otherwise, repair or replace it. Then go to step  11.
  2. Check the accelerator pedal position sensor. Disconnect the accelerator pedal position sensor connector D-138. Measure resistance between terminal No. 1 and No. 2 and between terminal No. 7 and No. 8. Standard value: 3.5 - 6.5 kiloohms Measure resistance between terminal No. 2 and No. 3 and between terminal No. 6 and No. 8. Move the accelerator pedal from the idle position to the full-open position. Resistance value changes in accordance with the accelerator pedal depression smoothly. If the resistance is normal, go to the next step, otherwise, replace the accelerator pedal position sensor. Then go to step  11.
  3. Check the continuity at accelerator pedal position sensor harness side connector D-138. Disconnect the connector D-138 and measure at the harness side. Measure the continuity between terminal No. 1 and ground. Should be less than 2 ohms. If the continuity is normal, go to step  7, otherwise, go to the next step.
  4. Check connector D-135 at PCM for damage. If the connector is in good condition, go to the next step, otherwise, repair or replace it. Then go to step  11.
  5. Check for harness damage between accelerator pedal position sensor connector D-138 (terminal No. 1) and PCM connector D-135 (terminal No. 91). If the harness wire is in good condition, go to the next step, otherwise, repair it. Then go to step  11.
  6. Using scan tool (MB991502), read the diagnostic trouble code (DTC). Connect scan tool (MB991502) to the data link connector. Turn the ignition switch to the "ON" position. After the DTC has been deleted, read the DTC again. Turn the ignition switch to the "LOCK" (OFF) position. If DTC P2121 sets, replace the PCM. Then go to step  11, otherwise, it can be assumed that this malfunction is intermittent. Refer to INTERMITTENT DIAGNOSTIC TROUBLE CODES .
  7. Check the accelerator pedal position switch. Disconnect the accelerator pedal position switch connector D-138. Check the continuity between accelerator pedal position switch side connector terminal No. 4 and No. 5. Standard value: Continuity (foot released from accelerator pedal) Non-continuity (accelerator pedal depressed) If the switch is operating properly, go to the next step, otherwise, replace the accelerator pedal position sensor. Then go to step  11.
  8. Check connector D-133 at PCM for damage. If the connector is in good condition, go to the next step, otherwise, repair or replace it. Then go to step  11.
  9. Check for short circuit to ground between accelerator pedal position switch connector D-138 (terminal No. 4) and PCM connector D-133 (terminal No. 38). If the harness wire is in good condition, go to the next step, otherwise, repair it. Then go to step  11.
  10. Using scan tool (MB991502), read the diagnostic trouble code (DTC). Connect scan tool (MB991502) to the data link connector. Turn the ignition switch to the "ON" position. After the DTC has been deleted, read the DTC again. Turn the ignition switch to the "LOCK" (OFF) position. If DTC P2121 sets, replace the PCM. Then go to the next step, otherwise, it can be assumed that this malfunction is intermittent. Refer to INTERMITTENT DIAGNOSTIC TROUBLE CODES .
  11. Using scan tool (MB991502), read the diagnostic trouble code (DTC). Connect scan tool (MB991502) to the data link connector. Turn the ignition switch to the "ON" position. After the DTC has been deleted, read the DTC again. Turn the ignition switch to the "LOCK" (OFF) position. If DTC P2121 sets, retry the troubleshooting, otherwise, the inspection is complete.
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