Worried

I daily an up to this point super well cared for and maintained Mitsubishi Montero. It's had all of its maintenance prior to my buying it with documentation and is up to date on things like timing belts etc. Its also super clean. I just had two oxygen sensors done. Now one time this happened before I had the sensors done and now it just happened again. The car just randomly rebooted/shutoff I was driving with AC on normal conditions had the radio playing streaming music from my phone this is my normal commute and have not had any issues.

Bam, reboot almost like a circuit breaker flipping engine immediately shuts off etc. The first time it happened I put it in park shut it off, turned it on nothing, turned it off, turned it on again it started right up all fine and dandy and no issues. The second time just now I actually got out and popped the hood to look because even the hazards would not go on. But maybe 1-2 minutes later I hear the car has power again turn the key and sure enough it starts right up everything fine.

No codes thrown when scanning the car with a obd scanner. I am trying googlefu for things but cant even begin to figure out what I should be checking? Battery/alternator tests? It's so sudden?

The most catastrophic and unanticipated car failures are usually the easiest to fix.

You've got a loose connection somewhere.

Start carrying a test light so you can diagnose while you rage out on the side of the road.

Sounds like an intermittent connection. Probably fuse/fusiblelink or MFI relay. You didnt actually state the year of your vehicle. I looked up the wiring diagrams for an 02 Monty XLS 3.5 and got some ideas just for funsies but i won't attempt to offer anything specific until i at least know what vehicle you actually drive.

I second the loose connection somewhere, but the hazards not working has me thinking it's not going to be an ignition switch as those should work regardless of ignition switch position.

Have you checked the connections at the battery? What about the ground connection from the battery to the vehicle? From the positive terminal to the starter and wherever else it may go? (In my Toyota's case the positive has a thick wire to the starter and a smaller wire going to a relay box)

What year Montero? Maybe there's wiring diagrams online we can pour over.

Definitely seems like it could be something loose. Whatever it is kills everything however even like I mentioned AC/Radio/Lights. I wondered if something could cause a short then the car actually kills itself to try and protect systems?

2003 Montero (not the sport the big one) 20th anniv 3.8 litre motor. I have a haynes manual for it. I checked the battery cables at the battery end and everything looked snug.

To be more specific. AC on driving slowly uphill both times once on freeway in traffic once at a light. Radio on, headlights on etc. Almost a popping like sound like when you suddenly unplug almost anything engine dies radio off etc at this point car still has power because the dash is lit up with the typical your engine just died lights/isnt started etc.

Shut off key, turn it back on and that's when nothing was on. The first time I just did that again and everything was fine. The first time I also was able to turn the hazards on while I was doing this just fine.

A dirty/loose battery connection can do that.

Start there. Clean both battery connections at the battery, inspect the cables and follow them to their terminus and check the connections there.

Next is ensuring the various connections, especially the grounds, in the engine bay are clean, right and protected from corrosion.

My uneducated guess is a loose ground wire on the exhaust side of the engine bay.

Under some extra load going uphill with the a/c on. Extra heat being generated causing slight expansion, motor/transmission possibly moving ever so slightly to the rear during the climb, could be enough to break a weak ground connection.

My guess would be to see if there is a fuze that is tripping and resetting. Could be a loose ground cable or somthing shorting under load tripping it. It cooles down and resets.

Going to follow the wires and check out the grounds tomorrow morning see if I can spot anything.

I just went through a similar problem on a friend's Jeep Cherokee. It would die, idle eratically, run badly. Turning on the blower motor would sometimes make the engine quit. Turned out to be dirty battery terminal connections and dirty grounds.

I would start with the ground side first. that's usually the problem with a large scale failure like you're experiencing.

Hungary Bill wrote: I second the loose connection somewhere, but the hazards not working has me thinking it's not going to be an ignition switch as those should work regardless of ignition switch position. Have you checked the connections at the battery? What about the ground connection from the battery to the vehicle? From the positive terminal to the starter and wherever else it may go? (In my Toyota's case the positive has a thick wire to the starter and a smaller wire going to a relay box) What year Montero? Maybe there's wiring diagrams online we can pour over.

I had a "similar" intermittent problem (as in zero power ANYWHERE… interior, dash lights, flashers …nothing) with a beater Suby that turned out to be a VERY hidden loose connection in the "bundle of snakes" wiring at the pos terminal off the battery … once found and fixed .. all problems went away

First rule of electrikery is that when it starts to behave like the star of the EXORCIST, you have a bad ground.

NOHOME wrote: First rule of electrikery is that when it starts to behave like the star of the EXORCIST, you have a bad ground.

I'm keeping that one

The only thing I could find was the negative battery cable was a little loose, loose enough to be turned easily and pulled off. I tightened it up. I tried following the wires under the car to find the firewall ground but was not able to follow it very far before it got hidden inside a cable management plastic tube. That tube went down to the o2 sensors etc under the car

What oxygen sensors did you use? I've had similar issues after replacing O2s with Bosch O2s. The crazy thing is that others experienced the same thing.

It's because you're looking for a replacement commuter car and its becoming self-aware.

flatlander937 wrote: It's because you're looking for a replacement commuter car and its becoming self-aware.

You are probably right, when you want to get rid of a car it starts throwing tantrums.

In terms of the oxygen sensor brand I am not sure what we went with they were not cheap however. And the first time this happened was pre the new sensors