Hey!, where did 4th gear go?

[outinthewoodsnf]

Recently we bought a 2004 Aveo for our daughter, and got ripped off. Car lasted a day or 2 when I noticed the coolant was low... I put antifreeze i it and u couldn't see thru the smoke to back up. Took her apart thinking head gasket but the head was cracked,,,, and a rod bent... Bought another engine from 05 with 75000k, which seems to be running ok, no overheating. Starts & idles fine, but now there's no 4th gear. It puts out : P0300,P1781,& P0700, I've read that random misfire causes the ECU to block 4th gear,& they are known for bad valves. They say I an get a Crank Sensor Relearn, but I wonder if the misfire is still being detected, will the problem just return?,,, at this point I just want 4th back and I'm not concerned about the CE light, or any supposed misfire. Is there any way to bypass this system to have the gear back?

[petrified.rabbit]

the odds are that you either need wires or a coil pack, or both. That will probably fix your issue.

[06T200]

So just curious, does it throw these codes immediately, or while you are driving it? Were they there with the old engine? Also I assume you checked basic stuff like ATF fluid level, and that nothing was left disconnected during the motor swap. When I am hunting down codes, I like to use a process of elimination to arrive at the bad part. I often find codes that pop up in sort of a chain reaction, and often times was something simple like a loose connector, or I added in too much ATF - as examples. Seems like anything will put the trans in "limp mode" (no 4th gear). When you clear the codes does 4th gear work till the MIL appears? - There are ways to 'tweak' the code within the ECU/TCU, but that info is very hard to come by unless you speak Russian and are really handy with assembly code. There are "updated" software revisions that can be reflashed to the ECU/TCU via GM's Tech 2 hardware, or a tis2web subscription. I would suggest to go here: https://tis2web.service.gm.com/tis2web and enter in the VIN of your Aveo and see if there are any updates for your modules, some updates address false DTC's being thrown. Not sure if this is your issue, but it may be of some help in chasing down intermittent codes. From what I have read some Aveo's went out with some buggy firmware in the MR140 units. FYI

[outinthewoodsnf]

I replaced the coil pack & wires, and reset the codes. The problem came back as soon as I accelerated on the highway.

[outinthewoodsnf]

It doesn't put the codes out till u drive it,.... The engine light was on with the original engine, but idk what the codes were,,,, however, 4th gear worked fine with that engine,,,, I hadn't checked the fluid because I never lost any and it was ok before,,, I also couldn't find any unconnected wires,,,, I've read that the random misfire code will do this to the tranny,,, to be honest, I'm really running out of patience,,,,,I will have a look at the site u suggested tommorow and see if that helps... Thanks

[06T200]

Same codes as before? ATF and coolant are topped off?

[06T200]

Reason I asked is it took me about two weeks to get an intermittent p0700 with MIL and limp mode '3 speed' shifts, to go away, wound up being the ATF was too high . 2500+ miles since then, no MIL. but I did not see the misfire code like you. this was on an 06.

[outinthewoodsnf]

Hmmm, I didn't check the previous codes, the coolant is topped up, but I haven't checked the ATF, however I will do that tommorow just to be sure. Tks

[06T200]

I looked at my service manual re: your misfire issue, and there is a 'misfire test' you can request to the ECU, I will assume it fails this test, hence giving you the p0300. Im not sure what your obd setup allows you to do. Also going off an older post it was suggested to do the idle relearn, see here: http://www.aveoforum.com/forum/f108/...98/index2.html

Good to try the cheap stuff before driving it off a cliff, or so I learned LOL

[06T200]

I did another search, and founds lots of posts on this misfire problem, much the same as yours (engine swap), and many were dead ends. One user explained that he had one 'fixed at the dealer', but did not know what was done to address the P0300. Sure would be nice to know if they are just pushing a (SAE J2534) re-flash to the ECU w/tech2, or if they are actually adjusting/relearning some sensor... So I have not found much on searches. f yi