Loosing 5v reference signal to map and tps, cycle key a few times fixes

I have an 03 accord 2.4 coupe that recently started having some issues, at first it threw a code for tps and map so naturally instead of investigating I just put new parts on it, then after awhile the problem started getting worse, here’s what the car does ONLY after sitting more than 4 hours. You start the car and within 5 seconds it dies and looses 5v to the map and tps maybe more but the map and tps is all I’ve checked. Weird thing is when it is acting up and dies the left turn signal comes on briefly. You cycle the key 2-4 times and the car will run great for the rest of the day, any input would be appreciated as I don’t know where to start now

I forgot to mention I also have a code for a bad rear 02 sensor, I was really thinking the map or tps was grounding out

What are the weather conditions when this is happening? Is it really cold/hot?

Due to when it’s acting up, I would suspect a sensor shorting out pulling down the ref voltage. Unplugging sensors is the way to go here. Does the voltage slowly climb back up or jump to 5 instantly?

It’s pretty chilly, 30-50 degree mornings, 5v will instantly come back, on first start after sitting I’ll have the 5v for about 3-5 seconds then drops to nothing, start it 2-3 times and it’ll come back. The thing that really throws me off if the left turn signal lighting up whenever it messes up.

If the unplug it test isn’t fruitful, you may be having a power problem (think relay failing). I pulled a diagram on my laptop saved ready to upload here whenever I finish up here at this dealership but got a couple other cars to deal with. In the meantime, when it acts up and stalls don’t touch the key and just leave the key in the same position you try tapping on the relay that powers the PCM. If you don’t get 5v ref back use a test light at the relay and see if you have what you need there to make the relay work.

Do you have a scan tool that can read enhanced data? Does it become a no com, when it stalls out? (I would assume it’s a no com) Monitor the ignition switch if possible. I’ll be able to help better once I can dig in and upload the diagram (seems like a fairly simple circuit)

My theory is maybe it's a bad contact in the ignition switch after reading that you fix it by cycling the key over and over.

While the 5V is missing (critical), key on, can you do some checks like see if the Windshield Wiper Motor works and if Fuse 19 remains hot at key on?

If I don’t shut it off it will never regain 5v, one thing I have noticed is that it makes a odd noise near the relays when it messes up, almost like a whine and will come and go with the turn signal. My scan tool continues providing data during the outage so I didn’t figure it was the relay to the pcm.

Everything continues to work during the outage, it’ll light up left turn signal for a second and other than that it’s the only thing that changes, I don’t really think it’s in the ignition, I still have power to everything else, fuel pump runs, wipers work, turn signals, everything that isn’t powered at key off works

Can you get to the pcm and locate the 5 volt reference wire and next time it acts up just cut the wire where you can fix it easy. If it restores the 5 volts issue is under hood sensor or wiring if it doesn’t you can eliminate all of that in one test

I’m not sure which wire goes to map/tps or I would

There’s got to be more than the map and tps on the reference wire. I think another member posted the wiring diagram

Ok I have an update, right before the car starts running bad on startup I hear a relay by the hood release click

Turn signal must has something in common with ECM, and it can be + or -!?

Suselman92 wrote: I’m not sure which wire goes to map/tps or I would

Here's wiring diagram

Exterior lamps:

I would assume I’m loosing 5v to other sensors as well, changed pcm relay, srill does same thing, car starts, idles for a few seconds, relay clicks and car dies, when I say car dies it doesn’t die from lack of fuel or spark, it will stay running if I give it gas, it just dies from loosing tps signal. Honestly the car will probably end up going to the junkyard in a few days

If it was in fact the ignition switch wouldn’t it not run at all? The thing that really stumps me is that the car never did this prior to the throttle body replacement, it shifted bad,idled high and the shift interlock release wouldn’t work, but it never ran bad or lost 5v

John Curtis wrote:

If the unplug it test isn’t fruitful, you may be having a power problem (think relay failing). I pulled a diagram on my laptop saved ready to upload here whenever I finish up here at this dealership but got a couple other cars to deal with. In the meantime, when it acts up and stalls don’t touch the key and just leave the key in the same position you try tapping on the relay that powers the PCM. If you don’t get 5v ref back use a test light at the relay and see if you have what you need there to make the relay work.

Do you have a scan tool that can read enhanced data? Does it become a no com, when it stalls out? (I would assume it’s a no com) Monitor the ignition switch if possible. I’ll be able to help better once I can dig in and upload the diagram (seems like a fairly simple circuit)

Just want to thank you! It's funny how someone from almost 5 years ago could finally help me fix my months and months long problem! 

Bought a car on January. Come february it showed a P2138 code and for 2 months all I had to do was cycle the key and it would be fixed until it didn't. from then on until october, I would lose 5v on APS1 and have P2122 with P2138 sometimes, go into limp mode and engine cuts off at 2,500 RPM where it stutters until you upshift. getting to 6th gear I can just run it at 2,500 rpm max and 70mph max. so, I replaced the TB and the Accelerator Pedal because the sensors were built it. Nothing changed! Went to 6 shops and the dealership in the span of a few months. They checked mechanically and electrically and said that everything was how it should be. Until today while coming home I came across this post and tried to check the relays and fuse box. Turns out a plug was loose but was still making a connection somehow (and maybe the 2 sensor fuse as well) so I just pushed those down hard and viola! The plug went down significantly so I think that was it? problem fixed! almost sold my car at a significant discount! Thank you!!

2013 Hyundai Genesis Coupe 2.0T with P2122 P2138 Throttle/pedal Position Sensor/switch "D" Circuit Low