Not shifting properly

Tiny
SHADOWWARRIOR58
  • MEMBER
  • 2001 CHEVROLET BLAZER
  • 1.3L
  • V6
  • 4WD
  • AUTOMATIC
  • 185,000 MILES
Vehicle has been worked on for about two years now. I got it without knowing all that was wrong with it. It drove, I didn't see anything wrong under the hood, but apparently it was junk when I got it. That being said, it's drivable now, but was told there are still a couple of codes. One indicates the throttle sensor as included with the vacuum code. I can tell sometimes, it doesn't want to shift. I know it's not the transmission, and the engine is great. Could it just be a vacuum issue and not the throttle? The reason I'm wondering is because sometimes, the acceleration gets to above 4RPMs, and then shifts. Or, I have to let off the gas in order for it to shift. It couldn't also be the timing belt could it? I'm thinking it could also be a spark plug issue, but no codes come up for that. The vacuum code encompasses a myriad of issues that could be causing this delay in shifting, I'm asking if I should replace the throttle sensor to get started on fixing the issue. Thanks so much for all your help!
Tuesday, November 30th, 2021 AT 6:58 PM

11 Replies

Tiny
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Let's start with what the actual codes are, and we can determine possible causes from there.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

In short, you are correct that the code could be causing the shifting issue and that a vacuum leak could be causing the code.

However, without knowing what the code is, we are guessing.

I am going to attach the guides that will help with checking for a vacuum leak because we should check this just to be sure but if you can send the codes then that will help.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

However, we also need to check the transmission fluid and make sure it is full and in good condition.

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

If not, then we need to change that out.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Let's start with all this info and go from there.

Thanks
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Wednesday, December 1st, 2021 AT 6:33 PM
Tiny
SHADOWWARRIOR58
  • MEMBER
  • 6 POSTS
There are three codes recently. PO122, 300, 449. 449 is the EVAP Vent Valve, and the 300 is the misfire. However, I just gassed up the truck today and the shifting had absolutely no issue. So maybe I need a new gas cap? I also checked the transmission fluid a couple months ago. It was drowning so had the guy drain it to proper level. I get the fluids checked regularly, almost every week. Mom's boyfriend says that I need to replace the entire exhaust system, catalytic converter included. I don't think I need all of that. The last time I listened to him, I got my other Blazer taken away even though I bought it from the family he knows.
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Friday, December 3rd, 2021 AT 7:36 PM
Tiny
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Okay. That is good news. It is unlikely that the gas cap is causing a misfire but let's stay with the shifting issue on this post and then we can get another one started if any of the codes come back.

I am interested to hear more on the transmission being overfilled. Can you check it again today and see if it is still overfilled or has become overfilled again?

If so, you have a leak between the transmission and transfer case and more than likely the transfer case fluid is coming into the transmission. It normally goes the other way and fills the transfer case, but it is odd that you would get an over filled transmission unless you or someone previous to you getting this vehicle over filled it.

However, an overfilled transmission will cause all sorts of shifting issues so if you have not checked the fluid in a little while, let's do that and see where it stands today. If the vehicle is not acting up, then that is great and let's just see how it goes until it starts doing it again. We can't fix something that is not broken.

Thanks
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Friday, December 3rd, 2021 AT 7:58 PM
Tiny
SHADOWWARRIOR58
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  • 6 POSTS
The reason the transmission was drowning was because mom's boyfriend overfilled it when he was fixing it to be drivable. I had it drained some when I was able to drive it again. I can recheck it tomorrow on my way to work though to check that off the list of possible issues.
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Friday, December 3rd, 2021 AT 9:29 PM
Tiny
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Perfect. That makes sense and helps with one less possible cause of the transfer case.

Let us know about the fluid and then let us know if this happens again. If it does then we need to try and notice how you are driving and what type of terrain you are on as that may have an effect. Thanks
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Saturday, December 4th, 2021 AT 5:58 AM
Tiny
SHADOWWARRIOR58
  • MEMBER
  • 6 POSTS
I checked the trans fluid today and it's great. Nothing wrong there. I did wind up needing a quart of oil though. I have noticed the shifting seems to get worse the lower it is in gas. It's a weird connection, but that's what I've observed. Regarding terrain, I drive on flattop every day to and from work. Some of it is highway, but most is having to go through the city, which is nothing but stop signs and stop lights. And traffic. Not bad traffic though. BTW, it's not a 1.3L, it's a 4.3L, which, I should have known that. Silly me. When I accelerate, I know it wants to, but it's like it hasn't reached that point where it should. I don't like driving automatics; I miss driving a stick shift. Because of my experience with a stick shift, I think all automatics are screwed up in shifting. That's just me though.
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Saturday, December 4th, 2021 AT 6:34 PM
Tiny
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Okay. That is all positive news. So, let's address the throttle position sensor code first because that can cause shifting issues. The throttle input is used for shifting so that needs to be accurate.

I am attaching the testing below as this could just be a sensor issue but if we have a greater 5-volt reference issue then that may be causing all your issues.

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what questions you have. Thanks
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Sunday, December 5th, 2021 AT 5:59 AM
Tiny
SHADOWWARRIOR58
  • MEMBER
  • 6 POSTS
Oh, my goodness! Thanks so much for the info! Sorry I haven't replied in a bit, busy with work and schooling. Yay for higher education! I will take a look at this wiring harness to see what's up. Thank you again.
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Wednesday, December 8th, 2021 AT 2:39 PM
Tiny
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Haha. No worries. Thanks for updating us and we are here whenever you get back to us so no rush or pressure from us.

Thanks, and higher education is great when you are finished with it. :)
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Wednesday, December 8th, 2021 AT 3:37 PM
Tiny
SHADOWWARRIOR58
  • MEMBER
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Hi again. Life got busy. Anyway, I wanted to update you on the truck's condition. The shifting seems worse now. And I have noticed that there is leaking toward the middle of the underside, and I think it's on the left side too? I'm not entirely sure of the exact location, but I'm thinking it is indeed the cat converter. I can show you a picture, but I'm not sure it is a good way to tell. Let me know if you would like to see the picture. Thanks again.
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Monday, December 20th, 2021 AT 1:01 PM
Tiny
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Does the shifting seem to be all the time now or still when it is low on fuel?

The fact that you have a leak tells me we most likely have had the unit run low on fluid and it may not be low now, but I suspect there was damage done and we are just dealing with the aftermath.

So, I would suggest dropping the pan and seeing how much metal is in the pan.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

If you have more metal than what is coating the magnetic then we most likely are going to have to rebuild or replace the transmission.

Is there a reason you are thinking it needs a converter? I'm not sure how that relates to a transmission leak, but I may be missing it.
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Monday, December 20th, 2021 AT 5:12 PM

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