Hi There, I'm Clay a certified master automobile technician with 30 years of automotive repair and diagnostic experience.
From your description most likely the Park/Neutral position switch is at fault. The Park/Neutral position switch detects the gearshift position and sends the shifter position signal to the ECM. For safety, the Park/Neutral position switch detects the gearshift position so that the engine can be started only when the vehicle is in P or N gear position.
The ECM will also determine there is a malfunction if it detects that the Park/Neutral position switch sent either P or N position P or N position signal to the ECM while the vehicle is in motion. Usually a Diagnostic Trouble Code (DTC) will set. Related DTC's for the Park/Neutral position switch are as follows:
P1780 Park/Neutral position switch/Verify switch input
P0705 Park/Neutral position switch/Verify switch input
P0850 Park/Neutral position switch/Verify switch cycling
The easiest way to verify the Park/Neutral position switch is grounding the starter relay is to monitor the ground on terminal #2 of the starter relay as marked in the link below. If there is no ground at terminal #2 of the starter relay during cranking the starter will not engage.
Starter Relay Location Pin 2
I hope this information is helpful. If you have any questions or run into any problems let me know.
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