P18B9 BUICK - Internal Mode Switch 'S' Circuit Shorted
- Faulty Internal Mode Switch
- Internal Mode Switch harness is open or shorted
- Internal Mode Switch circuit poor electrical connection
- Engine Light ON (or Service Engine Soon Warning Light)
P18b9 Buick DescriptionThe 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.
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