Hello...I'm new to the forum and I'm hoping someone can help/guide me on some trouble codes I had pulled. With my wife and I currently injured we need to keep a tight budget so I’m hoping I can do this all myself or at least get some guidance so that I don't get ripped off. I recently had a mobile mechanic come to change the plugs on my Expedition while I was at work and he never changed them and charged us and took the plugs and wires knowing that my wife was unable to move that day...real nice taking advantage of a woman with a broken back and neurological damage from a car accident..right? And he know I had recently had three surgeries leaving me unable to do the job. Anyway...this is why I seek your assistance. So any help will be greatly appreciated.

To the issue at hand...

I am getting the following codes on a 2003 Chevy Monte Carlo LS with an auto trans; the car has ~102K on it. The car is shifting hard into most gears. Worse when warmed up. I was able to change the fluid and filter myself - not easy/fun in my current condition. It seemed to get a little better and we were able to take the car on a drive to NJ from VA for a funeral with no issues. Recently though; about 1000 miles or so after the fluid change the car seems to be getting worse; meaning it actually feels like it is shifting harder and harder each day..so now we don't drive the car.

I was able to have the following codes pulled at AAMACO (free):

Transmission related:
po720 Torque converter or Output Speed Sensor Circuit Malfunction
po1811 Long Shift This is a a GM code to the best of my knowledge.


Also the following codes were pulled and they look like a coolant sensor to me:

po128 coolant issue - Thermostat?
po420 Cat Conv - could be coolant issue though as it states The engine coolant temperature sensor may not be working properly.

AAMACO is telling me they think the transmission may need to be rebuilt. The cost $1,500 to $2,500. He stated it would be about $1,800 if he had to guess. I have seen the following TSB on this car and am hoping this would be the Pressure Control Solenoid Valve Assembly they refer too:

TSB #08-07-30-002 -- INFORMATION ON 4T65-E MN7, M15 AND M76 FRONT WHEEL DRIVE AUTOMATIC TRANSMISSION VALVE BODY RECONDITIONING, DTCS P0741, P0742, P0757, P842, HARSH SHIFTS OR SLIPS. *PE (NHTSA ID #10025561, JANUARY 01 2008)

Has anyone else had this combination of codes?

What would it typically cost to rebuild a transmission? Is AAMACO on the mark or should I seek out a smaller shop? I prefer to help out the smaller businesses especially in this economy.

Any thoughts on the hard shifting or the other two codes would be greatly appreciated.


PS I saw another 1811 code issue on here but that was in Jan and there was no resolution. I really need to save as much $ as I can (I'm sure there are many of us out there in this economy who understand this). Thanks Again!!!

 

AAmco is the LAST place I would take a car. They are paid to rebuild transmissions. That's what they do. It's like going to a barber to get a haircut. I'd take it to a reputable garage and get another opinion. And the P0420 is a catalytic convertor innefeciency code. My guess is you need a new catalytic convertor, and that is messing with everything. On the other hand, I'm also guessing you have the 4T60 tranny, and not the 4T65E, but I may be wrong here. The 4T60 tran's are crap compared to the 4T65E. I had 3 go out in 3 cars, all '01's.

Take it somewhere and get another opinion.

After reading your post again, I'm sticking with my opinion that the cat' is clogged.

 

Thanks for the reply Wayne. I have a few calls out to a few mechanics and I'm waiting for a reply from them. I believe it is the 4T60E transmission; at least that's what I saw on line. A woman my wife knows has a son who is a mechanic (I'm not sure if he does transmissions or not) who I know can help me out with the Cat. I already bought the O2 sensor (bank 1) but have not had the opportunity to put the sensor in (well I really need to buy the socket as it's too tight to get in with a wrench). Maybe I'll contact him and have him do the sensor and the Cat. It does have 102K on it...so it's probably due anyway.

I had heard of the Cats putting some Chevy's into "limp-along" mode; where you can't get the car to accelerate. It's probably the lesser of two evils anyway. I'll definately skip over AAMCO and look into another mechanic or two.

Can a Cat really cause the transmssion to shift hard like that?

What's your opinion on the highflow Cats? Would it make the car run any better? More HP? Or would it only be beneficial with a catback exhaust too (which I can't find for the LS)?

Thanks again for the reply.
Bob

 

P0420 is your cat. Been there, done that. They tried to tell me it was an o2 sensor, it wasn't, it was the cat. There are codes specifically related to the o2 sensors but I don't know what they are off the top of my head.
Don't know about the others.

 

I have had the usual battle with the cat as most. One important thing, what does your temp gauge read when the car is warmed up? I have the 3.8 but when I bought the car the temp gauge would only reach a quarter of the way. I think that because the car never got fully warmed up, the fuel system ran rich and then the cat crapped out. I ended up replacing the t-stat, temp sensor on the t-stat housing, and the cat. I did the 02 sensor while I was in there too for good measure.
A bad cat does have quite the effect on these cars but I'm not totally convinced that the cat is causing the crummy shifts because you said that after a fluid change it shifted better. If I had to start somewhere it would be the cat though. I'm not sure about the high flow cats. I have heard that some people needed 02 emulators after installing one though.

 

I have a Magnaflow hi-flow cat, and it throws P0420 codes, that I had turned off with a HP Tuner. That can be an issue, but for your '03 I'd get an O2 emeulator. You won't be able to run a hi-flow cat without dealing with it one of those 2 ways, and the later years are harder, because they have heat sensors in them, also, which eliminates the use of an emulator.

For the price of a stock cat, you can put in a hi-flow cat, and downpipe, and eliminate the U-bend pipe. Return the O2 sensor if it hasn't been used, and get an O2 emulator. When you're done, you'll have picked up a few HP and saved a few $$$ while at it!

And yes, the cat WILL mess with the tranny. Been there, done that. BUT! You MIGHT have tranny problems also. My opinion of the tranny is if it ain't TOTALLY broke, don't fix it. Shifting problems are not necessarily tranny problems. It is computer controlled, and something is messin' with the computer.

Have a garage do a pressure test on the cat BEFORE you do ANYTHING else!

 

Gentlemen, Thank you for the input. I'll get the Cat checked out (I'll have the change the O2 sensor anyway as it looks pretty crudy).

To answer the tempature question...the car does run very cool. Like 160 degrees when warm. Maybe 170. It's about 1/4 of the way up the guage - and the guage goes from 240 to 260. The thermostat is cheap enough like $10 to $12. This I know I can do myself.

It looks like the Magnaflow (not high flow) is about $177 or so at Autozone. Not as bad I a thought it was going to be. I'll have to see if this is something I can do or if I need someone to install it for me (due to the surgeries I have had).

So in short...I guess I''ll look at fixing the temperture and the clogged Cat (after getting it tested) to see if this fixes the tranny issue.

Do any of you know if they make acat back system for the LS? I've seen them for the Monte Carlo but they all say there for the SS. Can you use the SS cat back on an LS? I like the look of the dual exhaust and the sound I had on the Firebird we had nd the sound of the SS Monte Carlos with the Cat back systems. Maybe I just need to take it to an exhaust shop and get them to custom bend some pipes?

Thanks again. The Wife and I appreciate your help in this matter.

Bob

 

But I have a high-flow cat and I don't throw any codes

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You can put the SS exhaust on your LS you would just need to have a shop weld on a hanger on the left side.

I got myself a ZZP downpipe, it had a high-flo cat already installed, and got rid of the u-bend delete on my car. $260 for the best quality they had. + multiple problems solved.

 

I'm with everyone else on this....get the cat fixed before doing anything else...And like Wayne said, DO NOT got to AAMCO. They will hit you up for a totally new transmission, or fully rebuilt one, when in fact maybe you only need something fixed inside your tranny....

 

I contacted a local mechanic. He said the same thing about AAMOCO. In fact he laughed pretty hard. He said he knew they would want to rebuild it. He also mentioned that over 50% of the ones he has worked on do not need to be rebuilt.

I'm gonna take it to him to see what he thinks. He's about 20 miles from me though. So I may get a car dolly at U-haul to get it there...just to be on the safe side.

He been working on cars for over 30 years and has alot of certifications...so hopefully I'm in good hands. I'll let you know what he says.

Thaks for the advice on the SS vs. LS exhaust. I'll look into that further as lonag as I don't lose my shirt on this CAT/tranny deal.