Shop changed transmission fluid, and I started having problems 1k miles later. What should I do?

I think it is possible to remove and clean a catalytic converter, and in fact I am going to need to try it on one of my vehicles, which has had the CEL on for a while with the same code. Sure, I could pay $350 plus tax and shipping to buy a new aftermarket cat online, but if I can clean it up with carburetor cleaner and get the CEL to stay off long enough to pass emissions, that’s $400 or so that I can put toward something else.

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People do it all the time.

But they run the risk of having tranny problems shortly thereafter like the OP.

I don’t think wrong fluid was added.


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The OP already told us the following:

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I don’t think a 100,000 mile transmission fluid and filter interval is excessive. Or maybe I have just been very lucky. I have changed the transmission fluid and filter in the following vehicles and approximate mileages, and none were really bad:

  1. 2004 Toyota Corolla, owned since new, changed at around 90,000 miles. No debris found in the pan, just minimal shavings on the magnet.

  2. 1995 Dodge Caravan, bought used with about 125,000 miles, changed at around 125,000 miles. No debris found in the pan, just minimal shavings on the magnet.

  3. 2002 Daewoo Lanos, bought used with about 80,000 miles, changed at around 90,000 miles. No debris found in the pan, just minimal shavings on the magnet.

  4. 2000 Chevrolet Silverado, bought used with about 210,000 miles, changed at around 210,000 miles. No debris found in the pan, but the magnet was full of shavings. Knocking on wood that the transmission continues to work well for a long time.

  5. 1998 Plymouth Voyager, changed the transmission fluid and filter for a friend, had about 210,000 miles at the time. Lots of fingernail-clipping size shavings found in the pan, but amazingly after putting a new filter and new licensed ATF+4, the transmission did not give any problems, and this person is still driving the van now, almost 5 years later.

I doubt the transmission service damaged the transmission. If the transmission is damaged, it was already damaged or worn enough to need repair before the transmission service.

It’s possible if the transmission service was done solely using a flush machine, rather than removing the pan, cleaning the gunk from the bottom of the pan, and replacing the trans filter, if pan wasn’t removed & it was only a flush job, that could possibly cause a problem that was soon to show anyway, but show up very soon after the flush.

So what should you do? Ask your shop to make sure the engine isn’t the culprit, and in fact the problem is the transmission. If it is in fact a problem w/ the transmission, at that point I’d be inclined just to ask my shop to do the whole transmission service job again, making sure they remove & clean the pan and replace the filter as part of the job. If problem remains, time for a visit to a transmission shop for another transmission or rebuild of this one.

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That question was addressed.

Just trying to be thorough here (and making sure we aren’t missing something here), so if while driving when the RPMs are high, if you give it more gas then the RPMs get higher but the vehicle stays at the same speed right?? Meaning giving it more gas only makes the engine rev up more while the vehicle moves at the same speed with NO acceleration…

And next question, why did you at 100K miles suddenly decide to change the ATF, was the vehicle doing anything strange or different then normal and you were trying to solve an issue??

Check the fault codes again, in addition to the catalyst fault you may have a failing ignition coil.

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No, it isn’t

For a 2005 Camry, the correct fluid is T-IV

Okay, so we know you have P0420 . . . thanks for the information

You want to see just how much it’s affecting drivability?

Perform a backpressure test and report the results

Do you live in a state with emissions testing?


Why? Do you even know if your problem is transmission related? What you’re describing could easily be an ignition related misfire?

What kind of reputable professional shop installs fluids that customers bring in?

The car is on its second catalyst at 100K miles. That alone is cause for concern. What’s killing the catalysts?

Even if the problem is found to be transmission related, changing the fluid certainly didn’t cause the problem. It was lurking in the background anyway. It’s not like the transmission was going to last another 100K but putting new fluid in it ruined it.

This is all speculation because we don’t even know what is happening with the car.


The RPMs would mostly stay around 2000 because I stayed at a safe slow speed. I did notice one time today that the RPMs rose to 3000 after pressing harder on the accelerator, and at that point the car didn’t move faster. The car remained at the same speed. I didn’t really experiment with this much though because I was concerned that my car would break down in the middle of traffic. I can’t really say with certainty what the situation with the RPMs is.

I decided to get my fluid changed at 100k mainly because I got a torque converter code. I procrastinated for a long time on getting the fluid changed. I hoped that the fluid change would get rid of the code and prolong the life of the transmission.

I drove the car today to drop it off at the auto shop and have some new info:

I drove my car to the shop today. When I stopped at a red light and was ready to drive again, the car wouldn’t move with my foot on the gas pedal. I had to turn off the engine, and restart it to get it moving again.

I have a P0420 code and a P2423 code. These are both codes I’ve seen frequently. I first seen the P2423 code when I put a spacer on the o2 sensor to get passed emissions inspections. I thought the 2423 code went away when I removed the spacer.

I’m wondering now if the P2423 code is related to the problem I’m having now.

When I explained the symptoms to the auto shop, they said it could be a clogged cat. I’m not sure if he is saying that because its what he legitimately believes or if he doesn’t want to take the blame for the transmission work he did.

I guess I have to wait for what he says tomorrow.

That sounds like flair up (slipping)…

Now we are getting somewhere, any idea what that code(s) was??

IF (cause you didn’t say) the engine revved up and the vehicle didn’t move then most likely your transmission fluid is very low or you have wasted the transmission…

IF I am understanding you on this, you have multiple issues on top of a transmission failure…
Here are some common issues with your transmission, sounds like a few fit yours from the info you have given…

Shuttle shifts, bind-up or flare on 2-3 shift, slips with throttle in 3rd and or 4th, TCC slip codes as well as solenoid performance codes.

BTW, before you spend a lot of money on a new catalytic converter, you need to make sure you are willing to spend the money on a transmission rebuild or used one just incase and vice versa…


Hang on a minute…you took an 18 year old car in a questionable state of repair that also had a transmission fault code to a shop who did what you asked them to do, and you’re blaming them for a possible transmission failure that was coming anyway?

I would laugh you out the door.


P2423 is for the rear catalytic converter on a Partial Zero Emission Vehicle.

Engine burns 1 quart of oil each week. Front and rear catalytic converters failing. Torque converter clutch slipping. New transmission fluid.

I don’t see a long future for this car.

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Before I had the work done I specifically asked the mechanic if he was sure it wasn’t too late to change the fluid. I told him the fluid had a light brown color, it hadn’t been changed for 100k miles, and I’m worried that changing the fluid can damage the transmission. He said everything would be okay.

That’s why I would blame him.

Welllllll, couple of things, he was right, changing the fluid will not damage the transmission, but he was wrong saying everything would be OK without test driving the vehicle and or checking for any codes to make sure nothing was off with the transmission, and the worst mistake he made was trusting a DIYers self diagnostic of a transmission issue, unless you failed to mention that part of it to him… So you are both to blame there…

And it is hard to blame the (any) mechanic for your neglect of your own vehicle…

Not trying to be disrespectful, but it just irritates me when someone blames the mechanic for a failure due to the neglect of their own vehicle… It’s always someone else fault… :man_facepalming:


Changing fluid does not damage a transmission. That’s a simple fact. If the only thing holding a transmission together is the burnt gritty fluid then failure is just around the corner anyway, new fluid or not.

Your transmission was already failing, you had some sort of torque converter fault code. That could be related to the torque converter, the valve body inside the trans, or an electrical issue. Without proper diagnosis and inspection, a fluid change was just a dart throw in the dark.

There is no blame for the shop to accept. Your car is old, it’s broken, and more than one system needs to be fixed according to what you say. You have now been advised by a handful of very qualified and very experienced automotive professionals. Bear that in mind before you try blaming a shop for something.


Isn’t the mechanic the expert though? He should know whether or not it was safe to change the transmission fluid.

If he didn’t change it, I likely could’ve had many more miles left on the vehicle.

Whatever though. At this point, I’ll just focus on taking the right course of action.



The mechanic who changed the fluid looked at the car today and just got back to me. He said the problem is definitely a clogged catalytic converter.

He said this is the case because he disconnected the oxygen sensor and then was able to smoothly drive to 60mph with no problems.

He said disconnecting the oxygen sensor allows the exhaust to not go through the catalytic converter. It goes through a different hole and makes a loud noise. Police would stop a person if they drove around like this, but it allowed him to identify the cause of the problem.

Does this make sense to you guys?

One more question: I had a P2423 code after putting a spacer on the oxygen sensor to pass emissions. I took the spacer off, and the code went away for a while. Do you think this code could have damaged the catalytic converter further due to improper readings from the sensor?