P18BD GMC - Internal Mode Switch 'P' Circuit Stuck Off Invalid Voltage Range

Repair Importance Level: 3/3
Repair Difficulty Level: 3/3   
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Possible causes

  • Faulty Internal Mode Switch
  • Internal Mode Switch harness is open or shorted
  • Internal Mode Switch circuit poor electrical connection

Possible symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)

P18bd Gmc Description

The internal mode switch indicates to the Transmission Control Module (TCM) which gear position the vehicle operator has selected. The internal mode switch consists of 5 separate hall effect switches. Each hall effect switch is supplied a 9 V reference circuit and a signal circuit from the TCM. Each signal circuit for each gear selector position will have either a voltage reading of 0.70-0.96 V indicting On or 1.68-2.38 V indicating Off. The voltage values on each internal mode switch circuit will change and are dependent on the position of the gear selector. The state of each internal mode switch A/B/C/P/S signal circuit is displayed on the scan tool.
OBDII Code P18bd Gmc - Internal Mode Switch 'P' Circuit Stuck Off Invalid Voltage Range - AutoCodes.com

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P18BD GMC Comments

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