I discovered my car “will start” in Rev, Drive, Etc. (all positions). I’ve had the car about six years and I’m not sure I’ve ever checked the switch function before, so it has possibly been this way all the time I’ve had the car.

So I took the console apart this weekend to see what was wrong with the neutral lock-out switch. The first thing is saw was the wiring harness connector “was not” plugged into the switch. So I think, OK, this is a no brainer just plug-in the harness and I’ll be good to go.

Well, it wasn’t all that easy. After I plugged the harness into the switch, it still didn’t fix the problem, the car still starts in all positions??? Next, I replace the switch with a new GM replacement, same problem (starts in all positions). I also tried adjusting the switch position and that didn’t help.

Another issue that puzzles me about the switch being unplugged is that interlock circuits “by design” must “complete” a circuit to operate. So, theoretically with the switch unplugged, the car should not start at all??? I checked it again with the switch unplugged and it starts every time.

Here’s one possibility, I’m the second owner on the car. So possibly when the lock-out switch came unplugged (with the 1st owner) and the car wouldn’t run. They didn’t find the actual cause (lock-out switch unplugged), so someone bypassed the neutral lock-out function somewhere in the system (but no idea where). However, I can’t see anything obvious in the console or under the dash in the wiring harness.

Maybe I’m missing something here on what's going on. Also, I think the switch provides some logic inputs to the PCM. Possibly there were some drive-train codes generated when the switch became unplugged and it’s in a fault mode now. And requires the codes to be reset for everything to work correctly again???

I’m definitely looking for some ideas with this problem.

WD

 

Looking at this wiring diagram of the neutral switch, I don't see how the car could possibly start without the switch plugged into the wiring harness and the switch working correctly???

WD

 

Where did you get that pic? It's definitely not for an F-body, the wire colors are wrong on the connector. There are 6 wires on the A4 shifter connector: 12 guage brown, 16 guage brown (smaller), yellow, orange, green, and black.

The car will run with all but 2 wires disconnected, the 12 guage brown and yellow wires. Brown is from the ignition switch and goes straight into the shifter connector, traveling through connector C200B (between kick panel and steering column). Then, when the shifter is in park or neutral, it completes the circuit through yellow, going into the theft deterrent relay, and from there to the BCM, giving the start enable command to the PCM.

So if your car starts with the connector unplugged, the previous owner probably shorted this circuit to bypass the connector. Of course with the connector unplugged, your reverse lights and hatch release button should not be working, unless those were shorted as well. There is no telling where that short is. You might need to get a set of the factory manuals and try tracking it down the entire circuit. Good luck.

 

The wiring diagram came from shoeboxe's website for a 96 F-Body. While the wire color coding is not the same, I believe it is electrically correct.

Here's a possibility looking at the starter and charging wiring diagram. If the contacts are stuck closed in the Theft Deterrent Relay, that could possibly cause this problem.

This is based on the park/neutral switch circuit applies a voltage to the coil windings to energize the Theft Deterrent Relay and apply the starter solenoid volatge. Again, if the Theft Deterrent Relay stayed energized, that would eliminate the park/neutral switch function.

WD

 

I found the problem and fixed it! Apparently with the first owner, when the park/neutral switch came unplugged initially and the car wouldn't run. Someone (obviously “not” a top-end technician) figured-out the Theft Deterrent Relay in the starter solenoid circuit “was not” energizing, so he bypassed the relay by striping and soldering the relay harness wires together.

That allowed the car to start and run, however, doing that removed the functionality of the park/neutral switch. The person who bypassed the relay wasn’t smart enough to find and fix the root-cause of the problem (unplugged park/neutral switch), so he just treated the symptom of the problem by bypassing the relay.

Basically, whoever did this work just screwed everything up. Now everything is working correctly again ("won't" start in Rev, D and "will" start in parK/neutral). I guess I paid some more LTX dues today, here are some photos.

WD


The tape on the relay harness looked suspicious.


I removed the tape and found the wires soldered together.


I cut and spliced the harness with butt connectors.


Relay reinstalled and wiring harness wrapped with electrical tape.


Park/neutral switch with wiring harness plugged in.

 

Say, Im doing an M6 to A4 Swap, and was wondering if you could tell me where the wires that come out of the NSS on the shifter go to?- and possibly pictuers of them going to wherever?

Thanks!

 

You may want to first look at a wiring diagram on Shoebox's site (different for the one I have posted). The Theft Deterrent Relay in the starter solenoid circuit adds to the complexity of the wiring. Also, it may be easiest to cut-out part of this harness from an A4 car.

WD

 

LOL- I tore out the WHOLE MOTHER F-er...