Engine won?t turn off

I was backing out of my driveway when I suddenly got an ABS failure and airbag warning. So I pulled back into my garage and turned the key, but the engine wouldn�t shut off. It just kept running. And then the weirdest part, when I turned the headlights off, it killed the engine. got a replacement ignition switch coming. If anyone can think of anything else or has experienced this before I am all ears.

Went back to the car. Turned it on and no issue. Backed it out of the garage again and the same thing happened. I even replicated the issue with the headlights. When the engine is running, turning the ignition off will not kill the engine. Turning the headlights off with the ignition turned on will not kill the engine, BUT turning the ignition off AND turning the headlights off kills the engine, and is the only way to do so without dropping the clutch/stalling. After clearing codes with durametric, the problem is gone. But does come back intermittently. The second time I tried it I was able to drive and no warnings came up on the dash. Only drove around for a minute and then parked it. The engine is running perfectly. These are the fault codes I get when it does happen. I will report if the ignition switch solves the problem, for anyone who may find this in the future. I was not able to find any threads about this on this forum. But maybe I'm blind.

This may not be the ignition switch at all. My theory is that you have a short in the harness causing power from the headlights to bleed back to the ignition circuit. You can diagnose with a circuit diagram and a multi-meter. Disconnect headlight switch, and ignition switch, and see if you have continuity between the headlight circuit and the ignition 'on' circuit. Testing at the fuse for each circuit would probably be the easiest way to start. If you have a short, then remove the fuse, and then test again at each end to see if the short is before the fuse, or after it. Others may have other better ideas, but that is my gut reaction.

My money would be on a bad brake pedal sensor , headlight switch and ignition switch that just happen to coincide. Good news all 3 parts aren’t horribly expensive to replace. It would be worth taking a look at headlamp connections. I had a marker bulb in the light unit burn out and when I went to replace it, the wiring was brittle and the insulation had crumbled. I cleaned the wires as best as possible and preventatively used liquid electric tape to insulate it. If after those are replaced and basic headlamp wiring checks out , and it still persists, I would go down the wire by wire route suggested above. As a note, when I had Weird instrument cluster and lighting issues, I replaced the headlight switch and it solved it. The thing sounded like a box of chiclets when you shook it. Exterior looked fine but the inside was crunchy and brittle and near dust. Hope that helps- scrh1

This sounds like a microswitch issue to me as well. They're all over the place but the error log indicates brake pedal so do some stretches and crawl into the foot well and check out the switch. Perhaps spray some DeoxIT on it.

Maybe a ground connection.

Thank you all for having a look. Guess I have some digging to do. Started the car today and it didn't have the problem at all. So it is quite intermittent. No time today but looks like I now have plans for this weekend.

I'm at a loss now, because I cannot get the issue to replicate since the first night when it did it three times. Am I correct in assuming that to diagnose a short/bad switch, it would need to be actively occurring? Seems my possible courses of action are: 1) do nothing until it happens again 2) replace ignition switch, see if happens again 3) replace all 3 microswitches mentioned before pre-emptively 4) ? what would ya'll do?

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Depending on the cost, probably do them all. They will all eventually go. Why not. One less thing to replace over the next 20 years.

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I would do #2.

How old is your car�s battery? A weak one can cause wonky behavior.

Lets not over think this guys. Its the ignition switch. Its what controls the ability of the car to turn on the switched power. It turns in a heck of a lot more then just the big relay on the back shelf so if the car was running normally when he pulled the key out it has to be the switch not killing the power. They r know to go bad and do random things. Just swap it.

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thanks. I replaced the ignition switch with a new one today. Although a cleaning may have sufficed it was filthy.. Not sure. Here are some pictures of the old part: hopefully this will solve the problem. If not I will be back to try some of your other ideas. thanks again you all.

after a while of no problems, it happened again. Same codes, same weird behavior where the headlight switch acts like the ignition. So It wasn't the ignition switch after all. Probably going to do the headlight switch and the brake pedal sensor, i guess.

Which brand of ignition switch did you replace it with? Just curious.

My bet is a short in your connectors or maybe wire harness. As there is not any way for the lights to turn on from the ign switch unless the light switch is already on, (or you have auto on lights in a 996 ?) Just as there is no way for the light switch to feed back to the ign switch to keep engine on, unless both switches were shorted simultaneously. B ut it would take both switches to be bad at the same time, and you already changed out the ign switch and have the same problem again... And with the plethora of unrelated fault codes it indicates a intermittent short, imo.... The way that switch looks, looks like it was water damaged, looks like it has rust coming out of it. And the back side of it is nasty like it maybe got real hot. That switch needed to be changed out for sure, you did the right thing changing it. Was your car in a flood, or left out in rain with top down...?

That looks more like dielectric grease on the non-terminal end. The terminals just look like normal 20 year old copper.

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Maybe, but I've never seen brown rusty colored dielectric grease. Most switches I've worked on have a white or clear grease. As for the terminal end, ya it does look like a 20 year old switch that was in the engine compartment not under the dash. To me it looks like some of that grease leaked out when switch got real hot. Regardless of ign switch looks, still think there is a intermittent short. I'd start by taking apart all connectors in that circuit and cleaning lubing them and reassembling them correctly, while looking for chafed wires.... jmo

That brown stuff is the assembly grease. They are all like that. The headlight switch absolutely can backfeed the ignition circuits. It has both unswitched power and switched ignition power.

I think the testing suggestion from @Icelia - Post #3 is a good place to fall back.

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URO parts. I actually had two in the garage so I tried them both and the problem persists. Maybe I should try an OEM part just to be 100% sure, but I've had decent luck with URO. I am suspecting the headlight switch because of the very odd behavior. It is like, once the car is running, the headlight switch becomes the primary ignition. I can remove the car key, and the car will stay running, but when I turn the headlight switch to off, the car turns off normally. Subsequently when I turn the headlight switch back to on, the car regains accessory power, even without the key in the ignition. I ordered the headlight switch and the brake pedal sensor from pelican yesterday because I'm comfortable with the price and replacing them, should be here tomorrow. If the problem persists after that I will have to start looking for a short in the harness but that doesn't sound like a lot of fun! Again, thanks for all the thoughts and replies! edit: no water or flood damage

I find �ro to be of decent quality also. I replaced my headlight switch with a �ro when I thought mine was a problem. My windows kept rolling down and then freaking out when I turned on my headlights. Turned out to not be the headlight switch. I had a short in the wiring to the driver side window switch. That was an easy fix and now I can drive in comfort in hot or cold weather with my headlights on. I gave my old factory headlight switch to a famous Youtuber (named after either a picnic basket stealing bear or a famous baseball player) and bought a spare �ro in case I ever need it.

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He's not your average youtuber.

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Looked at wiring diagram, You're correct, there is unswitched power at headlight switch. Didn't know that, thanks for setting me straight. So yes, shorted out headlight switch could back feed ign switch.... Yup, change out the headlight switch for sure....

I was an sticky mess but it wasn't my problem. Replaced the headlight switch and brake pedal sensor. And my problem persists. So, for those of you that called a short in the wiring harness early on, looks like you were right and I wasted $100 throwing parts at it. Now, how will I go about diagnosing this short. A few things are consistent: 1) Everything functions normally if the headlights are off. 2) If the car is stationary, and I turn on the headlights, nothing happens. 3) If the car is running, and the headlights are on, and then I start driving, I get "ABS Failure" "PSM Failure" "Drive to Workshop" 4) If I remove the key from the ignition the car stays running. If I turn the headlights to off, it kills the engine. I do have a multimeter and what I would consider beginners electrical knowledge. I checked fuses related to ABS and Traction Control as a first step, and they look okay. " Disconnect headlight switch, and ignition switch, and see if you have continuity between the headlight circuit and the ignition 'on' circuit." I will try this next, I guess I am just confused which hole in the ignition harness to stick the probe, and likewise on the headlight harness, but I suppose I could trial and error. "Maybe a ground connection." This I don't understand, not that you're incorrect. I just don't understand how to test this. Thanks in advance for any replies. I'm kind of stuck for now so any suggestions welcome.

For some electrical trouble shooting tips ,check out Ivan “pine hollow auto diagnostics” on YouTube.

another thing I noticed is my cruise control seems to turn itself on randomly and the clutch pedal doesn't turn it off. So I figured I'll throw another $20 at the problem by way of a clutch pedal switch. At least when I eventually take it to the shop i'll be able to tell them I already replaced all the switches.

Pull all the fuses related to the lights and retest. I believe all the top row fuses are for lighting; best check your manual to make sure.

Have you checked any relays? Maybe a relay is sticking in the �on� position. From what I�ve figured doing my motor swap all relays stay on for approximately 10 seconds after key is in the off position. Whatever is happening is keeping your ecu circuit alive regardless of the key position.

all the fuses are good. I haven't tested relays. Looking at a map now which ones do you suppose I should test? Ignition sensor? MFI? Fuel pump? Would that explain the behavior of the headlight switch?

By "pull all the lighting fuses" I mean to remove the fuses from the fusebox and leave them out. Then try your test again with starting the car, turning on the light switch and so on. I have not got the wiring diagrams for the .2 NA cars, so assuming the Turbo is the same as the .2 NA car then all the top row of fuses (the "A row) is dedicated to the lighting. Pull them all out. This will help isolate the problem to a specific part of the circuits.

Did you ever get to the bottom of this, @pulpo ?

I'm re-reading this thread and a bit puzzled by my post #25 because the issue did stop after I replaced the microswitches. I did replace the ignition switch, headlight switch, brake pedal switch, and clutch pedal switch. the ignition switch, brake pedal switch, and clutch pedal switch are all like $20 each so start with those and if that doesn't fix it try the headlight switch too. It did stop after I replaced all 4.