Weird Check Engine Light Issue

[invader166]

So this afternoon I got my first check engine light with my '09 Yaris AT.

It came up just as I was getting ready to go to work. I didn't want to be late, so I kind of ignored it. (it's not a long trip, but the area is inaccessible without a car)

The car started fine, drove fine and when I arrived, checked all the fluids. (I had just done an oil change not long ago) All were fine.
The only problem I can see is the gear indication above the odometer no longer displaying which gear I'm in (L, 2, 3, D, etc...) except for parking.

I wonder if it's not just a simple computer glitch and I should try to reset the ECU. (disconnect negative battery terminal)

Any ideas or suggestions?

[CTScott]

Usually losing the gear position indicates a failure of the switch on the tranny that feeds that info to the ECM.

[invader166]

Lovely! Too bad I don't have an ODB II reader to find out more. (been meaning to get one for a while)

Looks like it's a trip to the service department for me...

[JHSmith]

-invader166, I have this same issue right now on my '07 Yaris AT. I have a service appointment for this Saturday, please let me know of your progress and I'll do the same. BTW, is it very cold where you live? I live in Maine where it's been pretty cold, and at times like this I've noticed some funky electrical issues (could be a complete coincidence).

-CTScott, would a failure of that tranny switch lead to the check engine light illumination?

Thanks,

[CTScott]

-invader166, I have this same issue right now on my '07 Yaris AT. I have a service appointment for this Saturday, please let me know of your progress and I'll do the same. BTW, is it very cold where you live? I live in Maine where it's been pretty cold, and at times like this I've noticed some funky electrical issues (could be a complete coincidence).

-CTScott, would a failure of that tranny switch lead to the check engine light illumination?

Thanks,

Yes. The MIL should light with a P0705 code being stored.

[JHSmith]

-CTScott: Just tested it at AutoZone, it was in fact a P0705. Oddly enough though, the MIL was not illuminated at all today (but fortunately the code still registered). Since the light is off, do you think I'm safe at this point to not worry about it unless the MIL light returns? The vehicle starts and shifts just fine, even when the MIL was on.

[CTScott]

-CTScott: Just tested it at AutoZone, it was in fact a P0705. Oddly enough though, the MIL was not illuminated at all today (but fortunately the code still registered). Since the light is off, do you think I'm safe at this point to not worry about it unless the MIL light returns? The vehicle starts and shifts just fine, even when the MIL was on.

I would at least pull and clean the connector on the tranny (the large grey one by where the shifter cable connects).

[invader166]

@JHSmith It's actually pretty warm where I live, about 10 degrees C (50 degrees F).

I plan on going to see a technician about the issue on Friday, but something interesting happened today. I wasn't able to connect a reader and check codes yet, but this afternoon, I accidentally slammed the passenger driver side a bit harder than usual, and all of a sudden, the gear indication in the dash returned. MIL is still active though, but the car runs and shifts pretty smooth.

I'm almost thinking this could have happened because of a loose connection, but I wanna check the codes and also have a look at the tranny connector CTScott mentioned. It's not the first time I've had problems with faulty connectors on this car.

[invader166]

Update: So now the MIL is off without me having to reset anything. Problem solved?:iono:

[sheekeebut]

Well, if it turns off on its own, I believe it's trying to tell you that lately it hasn't had any park/neutral position switch circuit problems. The worst I could conclude from this is an "intermittent" problem, to be fixed only if the light comes back on and off enough to annoy you. Hoping it doesn't come back!

[JHSmith]

@invader166: I had toyota clear the code and the MIL is now gone... they said if the code returns that I should replace that (range sensor?), which is over $300. The non-illumination of the gear position continues to be a problem, although only intermittently, but the MIL has not returned.

@CTScott: I read that a non-start could result from this transmission sensor becoming faulty... about a month ago i remember while trying to start the car the engine would turn over, but not start. Then on the second try it fired right up like usual. Do you think this was related to that transmission sensor? Or if the sensor was faulty, would the engine not turn over at all?

[CTScott]

I would think it would not start at all, as the ECU would believe the car was in gear.

[invader166]

Interesting. I have had a couple of occasions in the past where the starter was cranking for a longer time than normal, but the engine would start. (could be a completely unrelated problem)
A few days ago though, I experienced the same thing as you JHSmith, engine would turn over, but would not start. Started on the second try just fine though.
So far, over 2 weeks and still no MIL or loss of indication of gear...