CEL persists following EGR Cooler/Valve/Intake Manifold Cleaning

2011 Prius with ~189K

My background: Just started learning basic maintenance on cars since 2017 and learned everything through reading forums and watching some Youtube videos.

This weekend I did:
-cleaning of EGR circuit from EGR cooler through to the intake manifold including the small passageways in the intake manifold. This was 2nd time; 1st time was at 125K no issues then.
-cleaning the following for the 1st time, as I didn't even know these components needed to be cleaned until this year:
- throttle body with throttle body cleaner,
- cleaned MAF sensor with MAF cleaner

Now with CEL while driving back and forth from work today (30 miles each way).


Thinking back to the work I did, 2 things I KNOW I goofed on (I figured out #2 but was too tired by the end to address #1)
1> Dropped the BOTTOM E8 TORX stud for the REAR of the EGR cooler (not the stud that connects to the side of the engine midway along the EGR cooler) somewhere down into the engine - not to be found again. I got the TOP TORX STUD in with the gasket. I opened up the plastic panel from under the car and the torx stud was nowhere to be found despite banging all over the plastic piece and feeling up into crevices around the engine. SINCE I COULDN'T FIND IT, I CHOSE TO OMIT this REAR BOTTOM TORX STUD AND THE ACCOMPANYING 10MM NUT. (I WONDER IF THIS IS THE SOURCE OF THE CEL? If so, why?)
2> Forgot to plug the black vent/vacuum hose into the front of the throttle body before starting up the engine - this caused a "CHECK HYBRID SYSTEM" light to turn on after the initial start - engine died after 25-30 seconds. I realized I had missed reconnecting this hose at the throttle body. After tracing back and reconnecting, the car started fine yesterday evening with a check engine light I prayed may be a residual of the hose disconnected.

I drove 60 mile round trip to work today with somewhat better MPG compared to pre-cleaning per the Prius MPG readout (from what I've read I am aware it's not accurate for real world MPG). But the car behaved differently...no stalling or hesitations.

The car seems to REV more than before the cleaning even on the way back home on neighborhood streets. REVs while stopped at the traffic light sometimes (not all the time) and at least a couple times while coasting at a slight downward slope in my neighborhood at the end of my drive home. Continued to REV once parked and at home until I turned the engine off with the power button earlier this evening.

I know how to pull OBD1 codes on pre-96 cars, and my 2005 Civic but, I have no clue how to pull the code for the check engine light on a Prius. I don't have a windows laptop for Toyota techstream. I DO have an OBD2 BAFX code reader(used for my 2005 Civic) and an Android phone - is Dr Prius sufficient to pull hybrid specific OBD2 CEL codes?

I scoured the forums all weekend with the hopes that I would try and do everything right...and yet here I am writing without a clear direction for the problem I caused while doing maintenance *BIG SIGH*. I'm just tired now physically and mentally...and can't figure it out.

Hopefully enough background to my additional questions below:
1> Engine REVVING at stop lights and coasting related to
- EGR cleaning?
-from my 12V battery (Optima Yellowtop) getting weak, which was last replaced in 2015 (~100K miles ago) getting weak? Interior lights and all electical/adio inside car is working fine without engine "ON" Lights are bright inside.
-a sign of HV battery going out? => Dr Prius app?

2> Check Engine Light
- related to the BOTTOM READ EGR COOLER TORX that I lost causing a leak in system?
- related to the REVVING? Seems like they are connected but can't figure it out.
- residual of leaving the vacuum hose off after the EGR/manifold/throttle body cleaning?
- Shall I disconnect the battery in the morning to reset ECU and CEL?

What next oh wise PC members?! FYI - I'm still planning to drive the car every day and I don't have time on weekdays to work on the car. 12 hour workdays and I'm tired by the time I get home.

 

I interrogated the code using both Dr Prius as well as torque and found the following codes:

P0441
P0455

P3191

While I'm trying to figure out how to post an image, the above codes showed up with the first two repeating consecutively followed by the third code only once.

For those that know the torque application, the first two codes were listed under historical and pending codes. With the third code, showing up under "logged faults"

 

Torque Historic fault codes by Illiterati posted Sep 27, 2022 at 8:29 AM

Screenshot_20220927-072116 by Illiterati posted Sep 27, 2022 at 8:28 AM

Screenshot_20220927-072414 by Illiterati posted Sep 27, 2022 at 8:27 AM

 

Finally figured out the albums and how to upload images. Hope the screenshots help.

BTW, this was what the fluctuating bars on Dr Prius looked like. Will need to see how to interpret all the values - appreciate insights about the battery screen.

Battery Home Screen Dr Prius 9/27/22 by Illiterati posted Sep 27, 2022 at 8:37 AM

 

Thanks for the information Mendel! To be clear, do you think that the REAR lower stud I dropped at the EGR cooler to exhaust manifold connection is causing an issue with the CEL?

Is this the stud you also kept off or just the painful one at the BOTTOM of the cooler? I guess I now have 2 of 4 torx studs missing from my EGR cooler. The TOP REAR and long FRONT

Seems it's common to see both P0441 and
P0455 together related to gas cap. My CEL was temporally related to work on the car as it was not there before working on the car.

P3191 perhaps when I left the front vacuum hose off near throttle body when I first had the engine start after doing the work?

 

Appreciate any other thoughts about the codes from what I've detailed above.

I plan to reset the code and buy a new 12v battery if voltmeter check tomorrow am(cool down overnight) is below 12.4v - in case it's causing the revving unless others have a different thought for why it's revving based on my screenshot of Dr Prius app.

Optima Yellow from 2015 has lasted til now; not as inclined to buy OEM Toyota with 4 year life span.

 

It was the original OEM battery that lasted 4 years. TBH, it's my wife's car and we take the kids everywhere. I wonder if it had a few cabin lights left on over those years. I have since replaced all interior lights with LED.

Good to hear 7 years is about the right time for replacement. Do you see symptoms with the battery revving engine before the interior lights start to dim? That seems to be my situation.

 

I was thinking similarly about a leak from the lack of both rear studs but was hoping you would say otherwise....oh well. Somewhere I'll find another few hours to take things apart again.

Mendel, I am kicking myself about not realizing the rear stud is the same as the side stud! I wish I would have thought about that side stud when I was frantically looking for it. I still don't know where the Lost torx stud went if not into the undertray. By now, it's somewhere on the side of a road around Northern California.

 

So, I looked under the hood again this morning and found I left a vent/vacuum hose? Off the front end of the tubing coming off the EGR valve.

Reset the codes using OBD2 - driven 120 miles today and no more CEL on Dr Prius, Torque, or dashboard. Plan to interrogate it again in a week.

@Mendel - I won't be replacing the REAR LOWER EGR cooler TORX that I lost connecting EGR cooler and exhaust manifold....N of 1 will see how this goes.

@ASRDogman - thanks for the info. 7 years too late.

I plan to replace my current Yellow Optima Top if voltmeter is less than 12.4...

MPG are mid 40s from 39-40 and relatively quicker acceleration. Purrs smoothly now!

Keeping fingers crossed

 

@ASRDogman - Oh my, I didn't mean to come off as being ungrateful or sarcastic. my apologies if it came out that way. I was stating matter of factly.

The OEM battery was replaced 7 years ago, so I wish I had known about the OEM battery warranty back then in 2015. Shame on me for not reading all the new owner materials back then...

I am grateful for all the input from the forum members. Hope you'll accept my apology.