Problem With Transmission or Electrical Issue With Codes P0785 P1810 and P1860

[Tiffany N Angel]

Hello! I got what I though was a good deal on a used 2002 Chevy Trailblazer from someone who said it needed a transmission solenoid and would cost under $300 to fix. So I bought the vehicle and took it to a garage and they told me it needed a whole new transmission and would cost me $3,000. I decided to get a second opinion, this time taking it to a transmission shop, and he told me the transmission was fine and he thought it was an electrical problem. Since I’ve had the vehicle it seems to shift fine, has power, and doesn’t slip. The previous owner said it had problems with acceleration but I don’t feel that. The first garage said it wasn’t going into 3rd gear but the transmission shop said that’s not true. The codes that are coming up are P0785, P1810, and P1860. The transmission shop replaced the ignition switch thinking that would correct the problem but after I left his shop, the check engine light came right back on and when I scanned it the same three codes were present. I’ve looked online and saw that it could be an electrical issue if there were 5 specific codes present but I don’t have all 5 of those codes. So I’m wondering what direction to go in? People are telling me to replace the solenoid and another part under the transmission to SEE if that fixes the issue but I don’t want to keep guessing. I am a female and don’t work on cars unfortunately. I am trying to find out what to do or where to go for help. I am in Wilkes Barre, PA. Can anyone help me? Thank you!

 

[Mooseman]

Welcome to the Nation. Sounds like a wiring issue too me. Check the connector for the transmission for any corrosion, the wiring for any chafing of damage. Download the manuals (link in my signature) and check the wiring schematics for anything common to all three that would affect them. Next, the pan should be dropped and the internal wiring checked. For all three to go at the same time is doubtful they are all actually defective.

 

[Tiffany N Angel]

Thank you so much for your reply! I was about 90% sure that it as going to be a wiring issue. Do I need a machine to also check the wiring besides doing a visual inspection? Sorry if that’s a stupid question but I’m not really sure what I’m doing. Haha

 

[Mooseman]

Not a machine but a multi-meter would work. You'd check continuity from the connector to the PCM connector. But for multiple failures, I'd first check the grounds first as that is common to most components.

 

[Tiffany N Angel]

Thank you! I made a post regarding my situation on Facebook and the garage who looked at my vehicle first responded to me and still insists that it needs a new transmission. Have you ever seen cases where people have this issue and it was in fact due to the entire transmission needing replacing? I just bought the vehicle at a good price but I don’t want to be sucked into a money pit and invest more money into in than I originally planned. The person I got it from said that all it needed was a transmission solenoid and me, being the trusting person I am, believed them so jumped on it. Now I think I’m regretting my purchase.

This is what the original mechanic sent me via Facebook after seeing me asking for help:

“Hello Tiffany and Angel I was scrolling thru Facebook and saw your post concerning your vehicle. I just figured I would offer you some information regarding your vehicle and hopefully help you in deciding what to do for a repair. Regardless weather or not you use us I just want to make sure you get the best possible repair at the best price.

P0785 is the shift solenoid that controls the 2-3 shift. This is a circuit code

P1810 Transmission Fluid Pressure Valve Position Switch Circuit

P1860 is a torque converter clutch code


The condition of the fluid, the codes you listed, the other three that were stored in history data in the pcm (engines computer) and the transmission data all points to failure of the transmission control module or TCM for short. The TCM is internal on the transmission and is part of the valve body. In this vehicle there is a small possibility that just changing out the TCM would repair this issue but, with the known issues with the transmissions and the cost to replace the TCM being well over $1,000.00 using dealer parts, fluids and programming we recommended a replacement unit. The TCM would come with a 90 day warranty the transmission is a 3yr 100k miles wtty I have replaced a couple TCM’s in these and have not had good luck with it working. The one or two we did get to work came back shortly after with problems slipping and or shifting.


I know that 2800.00 is a lot of money to spend but to charge you for what we call “bandaid repairs” I can’t do in clear conscience. I’d hate to charge you for a TCM/valve body and then still have to possibly replace transmission 3-6 months later.


I hope I don’t seem rude I just would hate to see you waste money so I tried to explain as best I can for you so whatever the course you decide you can make an informed decision.


I also saw that another shop replaced the ignition switch, there was an old history code for low voltage but we attributed that to a previous dead battery.


If there is anything we can do to help you make a decision towards a repair, or anything automotive related I’d be glad to help you in any way possible.


Lastly I’m so confident in our diagnosis that If it did not fix your issue I will not charge you for the repair.


I hope that some of this information helps

Thank you,


Please know that I am in know way trying to push you into a repair with us. I figured a little more information on the issue would possibly clarify things.”

Thoughts?

 

[Mooseman]

Right off the bat I can tell you he is full of BS! The TCM (transmission control module) is NOT in the transmission. On this transmission, they are external and on this platform, in the PCM itself. The PCM tells the transmission how and when to shift by controlling the solenoids inside the transmission, including the one for the torque converter clutch.

Go to another shop. These guys are shiftier than their transmissions.

 

[Tiffany N Angel]

Wow! I’m shocked to hear this because everyone around my area says nothing but great things about this mechanic and his shop. I did think it was strange that he was the only one who said I needed a whole new transmission though. I am going to try another transmission shop tomorrow so im hoping for the best. Would a transmission shop be the best place to go or should I try a garage that specializes in electrical issues?

 

[Mooseman]

A transmission shop because it may be an internal electrical issue, not just a wiring issue outside the tranny.

And to prove he's an idiot, here are actual links to what those codes mean:
https://www.engine-codes.com/p0785_chevrolet.html
https://www.engine-codes.com/p1810_chevrolet.html
https://www.engine-codes.com/p1860_chevrolet.html

You'll notice that none of these say that it is a mechanical failure of the transmission as a possible cause. They do say it could be an issue with the fluid (low or dirty) but all say that it could be a faulty solenoid or electrical connection issue for each of those.

BTW, what is the mileage on this truck?

 

[Tiffany N Angel]

It has 114,000 miles. The fluid is quite dirty but the 2nd place I went to (the transmission shop) said not to flush it because sometimes that does more harm than good. But I should still be able to drain it, change the transmission filter, and refill it and see if that helps, right?

 

[Mooseman]

Failures at that mileage are rare although not unheard of.

We never recommend a machine flush because they can do more harm than good however we highly recommend a complete fluid exchange, as per this thread:
Transmission Fluid Exchange (Flush)
Lots of good info and videos.

But, because you are having issues which could be internal (solenoids or wiring), you might want to check the internals prior to doing a fluid exchange to avoid wasting fluid. I remember somebody having similar issues and it was pinched or chafed wiring inside the tranny. Replacing the internal wiring harness fixed it in that case. It is unusual for three solenoids to quit at the same time except with a wiring issue.

My '02 (RIP) had brown fluid when I got it in 2011 and it lasted 5 years/100k after I exchanged the fluid. The tranny did eventually die of an actual mechanical failure and it was very evident.

 

[Reprise]

The 2nd shop has been doing a lot better for you than shop #1. If you want to be polite, you can thank shop #1 for his time, but as Mooseman said - do not let that guy near your truck, or any other vehicle you have. He's looked at it personally, and for him to tell you what he told you, in polite terms...he is either dishonest, or inept as a mechanic.

Lastly I’m so confident in our diagnosis that If it did not fix your issue I will not charge you for the repair.

For $1000 (which is way too much to replace either a TCM or PCM, and you don't even have a separate TCM in an '02) - you can put a *lot* of new stuff in a trans (and since he supposedly knows how transmissions work, he could probably completely rebuild it to factory spec for that cost). If he replaced the trans outright (for $2800), then of course it's going to 'work' when he's done. So take that with a grain of salt. Also, as I write this, I think that he sees you're not good with the $2800 for a new trans, so he's trying to reel you in with the $1000 repair, saying that he'll at least get it back on the road for you for that price.

The bad thing for you is that you're not experienced with automotive repair. And for what it would cost in tools & learning time (unless you're interested in learning, which counts for a lot) - you're better off either finding a good, honest mechanic, or enlisting someone you know (friend, significant other, etc.) to help you with this (and it's only fair to compensate them in some fashion.
Stuff like normal 'maintenance' (changing fluids, filters, etc.) is easy enough that you can learn that quickly, with minimum $ investment in tools, etc. And you'll learn more about how your vehicle works (and others that you may have in the future.)

As for (most) of the members here...I'll admit that many of us work on our vehicles because we think dealership costs are insane (and sometimes they don't fix the vehicles properly), and some of us even have the mindset that the only way we'll 'know' our vehicles are fixed - is to do the work ourselves. Generally, we'll save a lot of cash by doing it ourselves, too (and in some cases, the owner can't afford to pay a 'pro' to do it, but they have some mechanical knowledge, time, and money enough to purchase the parts.)

How you benefit from that is to see what we post here collectively...you can see what 'works', and what doesn't...alternatives to save time / effort / money when possible, etc. And as the old saying goes...it's cheaper to keep a good running vehicle, than it is to purchase a new one (although new ones are nice, have a warranty, latest safety features, more fuel efficient, etc.)

To answer your question about changing out fluid & filter... of course, you can do that, and it's probably time for it. And while I don't think it will 'likely' fix your issue...you won't be doing any harm, and might do it some help. Since the trans operates normally now, by performing a fluid / filter change, you'll be extending its life. Actually, assuming the issue is electrical, you won't be 'wasting' time / money on changing the fluid, either - even if it has to be drained to perform the 'real' fix. I won't lie - it's a fairly messy job, especially if there's no drain plug in the pan. But it is something that you could even do yourself, if you don't mind dealing with the mess.

 

[seanpooh]

So... I have a few documents which may or may not help. I'm trying to help, but the first step is make sure to have correct fluid level. Also, everything else in the documents afterwards is electrical diagnosis. Don't know if the trans shop you talked to has a guy who specializes it electrical, but they have access to all data or some other reference place to help fix your issue.

 

[Tiffany N Angel]

Hello everyone! Thank you all for all of the input! So it is at another shop and they told me that when they took down the transmission pan to check the wiring there and the solenoids that the transmission fluid was almost black and had the consistency of paint! I know why the first garage especially the transmission shop didn't mention this to me unless they never really looked. The first shop did say that there was a lot of metal in the transmission fluid BUT this shop said that's not true. The fluid is bad but there's no metal in it. He said whoever had this vehicle before me didn't take care of it. So he is draining the fluid and replacing that and the transmission filter. I have questions. 1, can fluid this bad be the cause for all of these codes to appear at the same time? 2, should i be having him flush all of the transmission out of the entire system or would just replacing the filter and filling up the vehicle with the recommended 5 quart replacement be enough? 3, is is possible to clean the solenoids or am I going to have to replace them? My friend told me that I got the codes because the solenoids were covered in gunk and weren't working properly and that I might be able to clean them? Thank you all!!!

 

[Mooseman]

Anything is possible but this shop is taking the right approach by replacing the fluid first and see what happens. The new fluid will have fresh detergents in it that should be able to clean things out. The solenoids may be permanently damaged and that will be determined afterwards. I still believe it's an electrical issue.

As for a flush (or rather a complete fluid exchange), the shop should do that given the very poor condition of the fluid.

The fact that he found no metal is very good news and the tranny is likely repairable without a rebuild.

 

[Tiffany N Angel]

Hi everyone! It took me long to get back to everyone because I’ve been out of town but I do have an update. So the Trailblazer is a yet another menchnic (this is now the 5th one I’ve taken it to) and I believe that he found the problem.... The radiator. He said that something inside the radiator broke and was spilling transmission fluid into the radiator and coolant into the transmission. He suggested that I get a new radiator and then flush the coolant and the transmission and hope that fixes the issue. But I’ve been reading online and everyone I saw with the same problem said that this had ruined the transmission and they had to either have theirs rebuilt or replaced. So I have a couple questions:

1. Could this have really been what was throwing all of those codes the whole time?

2. Is it true that my transmission is probably toast or is there a chance it can be saved?

3. If it may be saved, should I change all those solenoids or should I just flush everything’s and drive it to see if the codes pop back up?

Any other suggestions that you may have for me to relay to this mechanic to hopefully save my transmission I’d really appreciate it!

I’m perplexed that out of all the mechanics I’ve taken this to not one of them saw this issue before this one!!!

 

[Mooseman]

Maybe. He might have found something but never heard of a leaking radiator causing an electrical issue inside the transmission. I'm still adamant that it's an electrical issue, either outside or inside the transmission.

Just thought of something, there is a fuse for the transmission. All Should be checked.

 

[Reprise]

I feel bad for the OP...five different places have given her (?) five different causes.

If mech #5 is right (that the ATF and coolant have cross-contaminated each other due to the two compartments in the radiator being compromised), that is pretty bad. It *could* be the reason why the ATF was 'thick as paint' and 'black' (but that is just a guess, from the info we have).

If they've intermingled enough, what's in the coolant reservoir (white plastic tank with a black cap on the top with 'DexCool only' printed on top) will look similar to a strawberry milkshake. If you see that - the two have definitely intermingled (the auto trans fluid is routed through a separate compartment at the bottom of the radiator to provide cooling for the ATF.) If you don't see it in the reservoir, you may be able to detect it in the radiator, but it will be harder to detect there, unless you get something to extract a sample of the fluid (e.g.; turkey baster, etc.), and transfer it to a container where you can view it & examine the consistency (which should be similar to water, if all is well...and the color will be orange, as well). Note: Do NOT open the radiator cap after running the engine / driving the vehicle. You want to check this when the engine is 'overnight cold', so that you don't burn yourself.

Besides the radiator replacement, the cooling system will need to be completely flushed, and new DexCool (GM's name for their brand of antifreeze) installed. As long as the source of the leak is repaired, the engine should be OK afterward.

Now for the really bad news (again, if the coolant got into the transmission)...

Coolant / water inside of a transmission will damage it in short order (by swelling the seals & clutch material). There are two ways to 'fix' it.

The first is to replace all of the fluid in the transmission & the filter - and hope for the best. Unfortunately, some coolant tends to stay behind, especially in the torque converter, and that 're-contaminates' the transmission again (in truth, it was never properly 'de-contaminated). It's a roll of the dice as to if / when you'll start having issues with the trans (which may be as 'little' as fluid leaks developing, due to swelling of the seals - but the transmission otherwise continuing to operate 'fairly normally'... OR...an actual failure of the transmission, due to internal parts being compromised).

The 'correct' way to fix it (per GM)...is to remove & rebuild (or replace) the trans. At a minimum, you need to replace the following:
All of the rubber type seals
All of the composition-faced clutch plate assemblies including the band.
All of the nylon parts.
The torque converter.

Then thoroughly clean and rebuild the transmission, using new gaskets and oil filter.

Obviously, that looks like a lot of $ - and you'd be right to think that. It's probably cheaper to replace the transmission (either with a used one, like from a junkyard, or with a new / rebuilt one).

Now...with all of that said...and again, *if* the contamination issue is 'true'...
- You've stated the trans seems to work 'normally', currently (except for the codes, of course)
- You don't know *how long* the coolant has been in the trans (or how much), since you just got the vehicle.

- Given the above, it it were 'me'... I'd take the cheaper solution first (let's call it 'flush & pray'.) It may work for a day, a month, a year - or for as long as you have the truck. It will definitely be cheaper / less downtime than rebuilding or replacing the trans now.

Also, and I'll add this, based on the info you've provided us so far...
- "prior owner didn't maintain the vehicle"... in order to be more sure on this, you'd want to (have someone) inspect the entire vehicle, to gather evidence of same.

- Radiator failing at your mileage... it can happen, and the most likely cause would be if the original coolant had been left in it waaayyyy too long (or an accident of some type in the past compromising it, but then you'd likely *see* a leak)
The factory fill is rated to last the longer of: 100,000 miles *or* 5 years from new. What happens is that the coolant loses it's protective qualities and turns acidic - and you can figure out the rest. I can't see as I write this response how 'old' your truck is...but I seem to remember it wasn't too far over 100K miles.

Right now, except for the price you paid for the truck, you don't have a lot invested into it (time, parts, etc.) Depending on how much you paid for it, you may decide to just sell it for what you can get (if you sell it privately, it's best to tell the potential buyer what you know about the condition of the truck).

Finally, to answer one of your questions directly...

>>>1. Could this have really been what was throwing all of those codes the whole time?
Possible, especially if the trans has significant coolant contamination, and it has been going on for awhile. However, if that turns out to be the case, I think you'd be having more / other issues than that.

(I've kinda addressed question #s 2 and 3 above, so no need to rehash those)

The next step for you is to figure out which mechanic(s) are steering you correctly, and go with the one you trust (or can show the most positive feedback from other customers...and that's not #1, in our opinion).

Sorry to be the bearer of bad news. I wish it could be better.

 

[Mooseman]

@Reprise , very thorough answer and agree with the "flush and pray". I would flush more than usual to get as much of the coolant out. If it is really contaminated with a lot of coolant/water, it could be shorting the solenoids.

If the tranny winds up working well after the flush, I would do another mini-flush after a month or so just to try and get as much of that coolant out.

Hope it goes your way.