Limp Mode? With no codes?!!

[pbody]

I just recently purchased a 2010 Aveo LT with 103k miles that I was told needed a head gasket... I concluded after purchasing the car that the headgasket appears to be ok. I get 220-250 compression in each cylinder, no smoke, etc.

Fixing the newly purchased Aveo:

I immediately found what the car actually needed was an alternator since it would not stay running without being attached to another cars battery. While replacing the alternator I also replaced the oil cooler, which was leaking and showing signs of oil in the reservoir (what the PO thought was the headgasket), and I replaced the thermostat for good measure.

After getting the car to run, at first, it threw a misfire p0300 code and was only running on 3 cylinders. I then replaced the plugs and noticed the coil was cracked (same cylinder it was misfiring on), so I replaced that too. Now the car starts up and idles smooth with NO more P0300!!

Excitedly I tried to drive it, but it did not come out of 2nd or 3rd gear. It has no power and the RPMs stick (the needle comes down very slow). It only goes about 1-3mph. I was able to get it back to my driveway after driving it about 10 blocks. When it sits and idles it sounds fine. Idles around 650-800. No hiccups. It sounds good.

The RPMs returning to idle slow may be some sort of indicator, or maybe just limp mode? The last time I had a slow RPM like this was on a motorcycle and it had to do with the air/ fuel ration being off. Though on the Aveo there are not codes... No lean or rich, sensor bad, etc. Nothing!

I am baffled that NO codes are being shown at all while it is limping home. How is this even possible? What could cause something so serious that the car needs to go into limp mode and not show a single codes? It must detect that everything thats detectable (sensors, MAf, etc) is ok? Would a stretched timing belt cause this? I'm not sure if that has ever been replaced.

I'm obviously confused here with a ton of questions. I do not trust the dealer to pull hidden codes for me and for what they would charge me, I can ween issues out myself and resell parts to get some of my money back if needed.

Has anyone else dealt with such a mysterious issue on this car? What was the outcome?

[avguy]

How is the transmission fluid level and quality? Second gen Aveos (mainIly reported for the '09) have a history of transmission fluid and coolant mixing, which ultimately causes transmission failure. It might be best to drain the transmission fluid into a completely clean, clear container, in order to see if it's contaminated with coolant.

[pbody]

How is the transmission fluid level and quality? Second gen Aveos (mainIly reported for the '09) have a history of transmission fluid and coolant mixing, which ultimately causes transmission failure. It might be best to drain the transmission fluid into a completely clean, clear container, in order to see if it's contaminated with coolant.

The fluid looks normal. Especially for 103k. It looks like it was changed once or twice.

One thing I just noticed is that the fluid was overfilled. Probably from the PO. I emptied a quart out and it is now just above the high cold mark after sitting overnight.

I just drove it around the block two times after removing the quart of fluid. The first time it went into limp mode after 1 block. Second time I just drove in a four block circle and it did not go into limp mode this time but it was revving kind of high. At times it sounds like a bearing is bad (growling or grinding sound), but then the sound goes away and it shift fine for a half a block. So Im not sure that it actually is a bearing or mechanical issue despite how it sounds at times.

The shifting is slightly hard or not at all. It will rev high and make a sort of grinding noise like it wants to shift.

It seems like it could be a TCM issue. Is there a proper way to recalibrate things after a battery change? The computer has been wiped clean. The car sat for 8 months in the guys driveway...



On another note: Personally, I would rather not have limp mode. Just let the part destroy itself. The amount of time spent figure out what is wrong or money spent towing it and paying GM specialist to figure things out, could be spent on a working used engine and tranny. Is there a way to completely disable limp mode?

[avguy]

...One thing I just noticed is that the fluid was overfilled. Probably from the PO. I emptied a quart out and it is now just above the high cold mark after sitting overnight.

Just making sure you're checking it correctly. Startup, shift back and forth through the selections, and immediately check the fluid level while running, using the cold marks. If you checked it correctly, and the fluid was overfilled by a quart, that will typically cause air bubbles, and is definitely not a good thing.

Just confirming that in P or N the engine will consistently idle, rev high, and then come back to idle normally. If that's correct, and it's only able to do 1-3 MPH, then that's not limp mode (which would be up to 20-30 mph). 'Growling and grinding' is definitely not good and sounds much more like gears. You can confirm that by removing the tranny fluid pan, where you're likely to find metal fragments. If so, that's definitely a new transmission. No idea about the engine, but a compression/leak down test is probably a good thing to do at this point.

[pbody]

I checked it with the engine running. I did not shift through the gears. Either way, it is the correct level and I am still having the issue.

I did some more test driving and discovered that it does it in neutral/ park as well. The engine hesitates around 2-3k and stays there when I rev it. Or hiccups a bit and then goes to 4k, and then will jump down to 1500k... etc. So it is looking now like this is an engine issue.

Also, I am receiving a code P0137 (sensor 2 fault). This may be because I did not tighten the nuts correctly on the pre cat. I just gauged them by hand. I should have used the torque wrench... It could also be the cat is clogged as well. Which would explain a lot of this. I am going to remove the sensor 1 and see if that makes a difference. That should ween out the cat. I will then drop the trans pan to check for metal shavings. The trans does seem to shift fine when driving on flat ground. Though it could be Im just not reving it enough to cause the issue when driving flat or on a decline.

[avguy]

Running without the upstream O2 sensor is a good diagnostic step. But with that new information about the engine, I suggest you hold off on the transmission pan drop until the engine problem has been resolved. Once the engine is running well, you'll find out what (if anything) remains to be done with the tranny.

[pbody]

Found the issue!

With the o2 sensor out the car goes right up hills and shifts fine. When I looked in the sensor hole, I could see the honeycomb material is completely clogged.

Now the question is, can I unclog this with chemicals? The car is already a ULEV... California cats are insanely expensive.

update: I ordered a new precat. Hopefully the rear cat is ok. I noticed shavings (glitter) in the down pipe as I removed the precat. I may remove the rear cat and blow compressed air through the back of it. Maybe spray some carb cleaner in there as well?

[avguy]

... Now the question is, can I unclog this with chemicals? ...

Glad to read you're making good progress and moving in the right direction!

You can find all sorts of stuff online where people report cleaning out cats - one guy claims that a quart of lacquer thinner mixed in with the gas is the answer! Maybe so maybe not, but personally I'd never mess around trying to clean a cat. Just buy whatever parts you need and be done with it. Amazon and Rockauto typically have the best prices, but it's always good to shop around.

One other thought. How many miles on your Aveo? Although I don't know about CA law, I think the fed emission law warranties cats for 8 years/80K miles. If you're within that mileage, you should be able to get it replaced under warranty. And if not, perhaps CA has a higher mileage warranty.

[petrified.rabbit]

I think if there is any chance of cleaning the cat, it is while it is out of the car, and not running cleaner through the system.

It's usually filled with soot to start, but once it heats up, its like charcoal, or lava rock. And tends to be harder than the material the honeycomb is made out of. The problem with chemically soaking it is, the cat is a chemical reaction in the first place. You might change the "composition of efficiency" meaning you will still get codes. Soaking in water will probably rot the pipe. But reversing the "flow" might push the blockage back out, whether air, water, etc.

Replacement is the best bet. But no matter what you do, you need to make sure you fixed the problem that cause the clog in the first place FIRST. Or you will need one again.

The issue of California emissions, I think if i lived there, I would walk.

[pbody]

Well i thought I was going to clean the cat...



I imagine the rear cat is not looking so hot either. The o2 sensor was covered in metal and dented.


Also, there is a lot of oil leaking. Could be I installed the oil cooler wrong. ...not sure why I did not even look in the cat when I did the oil cooler. It was late at night and I was moving quick... Anyway, I replaced all the o rings and the gaskets are new... It appears its coming from the oil pan gasket... The head gasket is not leaking oil. Maybe there is so much engine pressure that oil is being pushed out of the oil pan??


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