Car Fails to start! Parking sensor??

[steve99]

Originally Posted by RZNT4R

Guys, really, holy shit, stop saying nonsense.

P0700 is a generic transmission fault code, think of it as being the transmission's way of turning on the check engine light.

P0851 is a PNP CIRCUIT LOW fault.

The transmission jerks hard in when put in gear because it's in fail-safe mode, as it feels it's TRS/PNP switch is unreliable.

The car doesn't have a clutch switch! JFC!

OP, unfortunately, throwing parts at something is a shitty way to do things. Go here, navigate to your year's repair manual, then Engine/Hybrid System -> FA20 Engine Control -> SFI System -> P0851 Park / Neutral Switch Input Circuit Low.

Step by step on how to find what's wrong, but the gist of it is, check for battery voltage across terminal 4 and 5 of the pnp connector with key on. Test light go bling = the problem is the pnp switch, or thereabouts. KEEP IN MIND! you threw a switch at it, is it correctly aligned? What caused the original no-crank condition? ASK YOURSELF! has the shift lever ever been hard to move at all? it is frequent for cars of a certain age to have shifter cables and linkages that start to bind. A linkage may bind at both ends of it's travel range, at one end of that range is the Park contact inside the switch, giving the shift lever a good slap is usually a good test of this, or just moving the lever to neutral to see if it starts there! It's called a park/neutral switch because the car can be started in either park or neutral!

Would a simpler test be


If car starts\cranks in park and neutral only but not other gears then the park neutral safety switch is likely



If it starts in all gears its faulty


If it doesnt start\crank in any gear its possibly faulty.


How does the ecu work out thte PN switch is faulty ?? Does is look for vehicle moving and still getting park neutral indication ?

[RZNT4R]

No, no no. Absolutely not. You've understood this backwards, upside down and on fire, and did so on every. single. point.

Cranking in park and neutral but not other gears is NORMAL OPERATION.

If it starts in all gears you likely have a short to ground on the ECM's switch sensing circuit, and that'll trigger other fault codes (like a circuit low fault) and a fail-safe operation.

If it doesn't start in any gear it could be any piece of wire or component in any circuit related to starting the car.

The ECU never said the switch was faulty! it said "There's a transmission problem!" (P0700)
and "I see ground on my switch sensing circuit when there shouldn't be! (P0851). The detection logic is explained at the top of the diagnostic chart.

The only sure fire quick test that rules out everything but the switch or linkage is cranking in neutral but not in park.

[Relogical]

Oops, didn't get a notification for the responses.

- The car does not start unless it's in park I believe, but I can always test out the other gears.

Thank you for the additional information!!

[Relogical]

Problem solved: Documenting the end results incase someone comes in the future with this.

- The parking/Neutral switch had to be replaced. The old one was fried. I bought a used one of a part out. New one is $200.

- My running lights in the tails were not working.

- The problem was fixed after noticing a harness that leads to the rear had tears in the wire. After soldering them back on, the gear selector light turned on and the running lights turned back on.

- In addition, you need two people to align the switch correctly. One holding on to the shifter and other aligning the switch.