Hi, I am a "do it myselfer" and I am frustrated by this vehicle. I acquired it a year ago and the check engine light would go on and off at will. Then it stayed on a few months ago, then the battery light came on and upon looking I see that the alternator tensioner is coming apart. So, I replace it, the battery and the alternator. The light goes off right after the repair and now a couple weeks later, the light comes on again!! UGH. So, i am going to take it to Auto Zone and find out what the codes read and go from there i guess. I need to get my emissions next month and I really don't want to have to spend alot of $$ if its something like the gas cap, will the codes come close to pinpointing the issue?

Yes, but don't listen to the advice that AutoZone gives you, they don't want to help you, they want your money. After you get the codes come back and post them, then we will help you solve your problem.

Autozone will read the codes for free. Bring them back and post on this forum. Be sure to get the actual code number (ex. P0175).


Hi, I am a "do it myselfer" and I am frustrated by this vehicle. I acquired it a year ago and the check engine light would go on and off at will. Then it stayed on a few months ago, then the battery light came on and upon looking I see that the alternator tensioner is coming apart. So, I replace it, the battery and the alternator. The light goes off right after the repair and now a couple weeks later, the light comes on again!! UGH. So, i am going to take it to Auto Zone and find out what the codes read and go from there i guess. I need to get my emissions next month and I really don't want to have to spend alot of $$ if its something like the gas cap, will the codes come close to pinpointing the issue?

Autozone will read the codes for free. Bring them back and post on this forum. Be sure to get the actual code number (ex. P0175).
Thanks guys, I appreciate that greatly :)

Thanks guys, I appreciate that greatly :)

Ok, so I take the truck to Autozone yesterday and had a very nice gentleman who is very knowledgable check it. It came up P1870 twice "Manufacturers transmission......" So, he asked me some questions and checked my fluid level and noticed it was WAY over filled. The history is that the transmission was fixed a little bit before I aquired the vehicle and it was done by a do it yourselfer. I dont know what was done and i dont know if the check engine light was on then either. So, I am wondering if this person didnt have the know how to shut it off and if there is a way to bleed fluid out. It sounds like a task, because it is a closed system and that most of the fluid is hard to access. So, now I am thinking maybe AAMCO would be trustful? I did notice that the tranny jumps into 2nd gear after i have gone at high speeds for awhile on a warm day, I dont know if thats a fluid thing or a mechanical thing.

Ok, so I take the truck to Autozone yesterday and had a very nice gentleman who is very knowledgable check it. It came up P1870 twice "Manufacturers transmission......" So, he asked me some questions and checked my fluid level and noticed it was WAY over filled. The history is that the transmission was fixed a little bit before I aquired the vehicle and it was done by a do it yourselfer. I dont know what was done and i dont know if the check engine light was on then either. So, I am wondering if this person didnt have the know how to shut it off and if there is a way to bleed fluid out. It sounds like a task, because it is a closed system and that most of the fluid is hard to access. So, now I am thinking maybe AAMCO would be trustful? I did notice that the tranny jumps into 2nd gear after i have gone at high speeds for awhile on a warm day, I dont know if thats a fluid thing or a mechanical thing.

Go and get the transmission filter changed and they will remove the excess fluid when they do that.

You need to change the filter anyways.

thanks for the info. Ironically I was reading some other posts regarding tranny issues and found I had the same symptoms and that it was a common problem (even AAMCO said what the problem may be and it corresponded with what i read here) so I am taking it this afternoon and they will run a diagnostic and if it is indeed the valve then they will fix it and correct the levels :) Keeping my fingers crossed!!

thanks for the info. Ironically I was reading some other posts regarding tranny issues and found I had the same symptoms and that it was a common problem (even AAMCO said what the problem may be and it corresponded with what i read here) so I am taking it this afternoon and they will run a diagnostic and if it is indeed the valve then they will fix it and correct the levels :) Keeping my fingers crossed!!

Please come back and let us know what they find.

will do, this is definitely a learning experience!!

good morning. Well, the news is not good. AAMCO checked and told me the code was a mechanical code not an electrical one so that eliminated the valve right away. The fluid shift which is supposed to be between 1-20 is at 100+ which indicates the clutch assembly or something like that is going out hence the warning with the hard shifts into second gear after traveling at high speeds. So, they suggest a rebuild for a lot of $$, I thanked them and went on my way, I have a friend who is experienced who will put a rebuilt one in for a LOT less and he has the equipment. I just need to find one for a decent price and figure out what voltage it is, 17 or below. I am also wondering if the same tranny was used in multiple years of the Blazer. This is too much fun :(

I doubt that it needs a complete rebuild. P1870 means it has detected that a transmission componet is slipping. When the code is set, the fluid is automatically boosted to maximum pressure, this is what is causing the hard shifts. The most common cause of P1870 is the valve body, these transmissions are known for having sticky valves in the valve body. I have a service bulletin about it that I can email to you if you want it.

Thats interesting. I hate going to those places who are not completely honest with me because I am a woman :( please send me whatever info you have and I will pass it along :)

They just LOVE to rebuild everything at those shops.

So, i am learning. I am getting second and third opinions tonite and tomorrow from more trusted (i hope) sources because I am told it could be as simple as a clog in the valve or something like that which just involves dropping the pan, etc. So I am holding off on purchasing a tranny. Gotta keep on truckin' :)

Thats interesting. I hate going to those places who are not completely honest with me because I am a woman :( please send me whatever info you have and I will pass it along :)
I need your email address to send it to you. You can send it to me in a PM if you don't want to post it here. The TSB covers what the code means and some of the common causes.

Thanks, Blazee, I read it over and went and talked to a tranny guy last night who explained what is probably going on and that AAMCO was a bit hasty without looking at the pan and filter and fluid inside because the fluid on the dipstick looked good and didnt smell burnt. So, I dropped it off with another trusted mechanic who will look at EVERYTHING and then let me know if its the valve body or if its gone beyond that.

Hi, all, letting you know that the tranny is BAD. There is metal all over the place and there is too many components needing replacement, soooooooo rebuilding would be a waste of $$ So i am getting a brand new one for less PLUS my transfer case was on its last leg (the chain) and the owner was nice enough to put a new one in at know charge, reseal and re fluid. and I am paying much less than what woulda happened at AAMCO i know, although its not cheap now but manageable. I figure, at this point it coulda been a whole lot worse!! It's a super smooth ride now :) Thanks to everyone for talking me through this!!