Undiagnosed Problem



Our 2005 Aveo with automatic transmission has 50,000 miles. About a month ago, the overdrive quit working, speedometer quit working, & check engine light came on, all pretty much at the same time. We took it into the dealer who said it needed an Output Speed Sensor & too bad we hadn’t bought an extended warranty, because it was going to cost us $700 to repair. We paid the $90 “diagnosis fee” & brought the car home. In carefully reading the manual, my husband found that this was, in fact, still covered by warranty. When he went back & pointed this out, they agreed. Then after having the part installed, it didn’t make any difference. After 2 more visits, they said that GM codes were not correct, that what it really needed was a transmission Output Speed Sensor, which was definitely not covered by any warranty, & would cost $370 for parts & labor. (They also refused to refund our $90, as they had promised to do.) This is not the first time this dealership has misdiagnosed a problem & we have no faith in them. We decided to have an independent mechanic install the part (genuine GM part) for less than $200 total. However, that still didn’t make any difference. We’ve talked to the GM District Manager & he was no help at all, offering us a year of free oil changes for our trouble. At this point, we’re disgusted with the whole thing & completely fed up with GM. We just want to get the car fixed so we can get rid of it. Any suggestions?

One other question: on the GM invoice from the first visit, after the description of the problem, it says “Invalid Vehicle Year”. What’s up with that?


What code(s) are associated with the check engine light? They would be in the format of P0123. They may be on your invoice or the dealer might be able to tell you what they were. Or many chain auto parts stores read them for free. Get them and post the exact code.


GM is operating under bankruptcy protection…For good reason…


Did the independent mechanic you went to do any diagnostic testing, or did he just install the part the dealer recommended?


Diagnose Code PO722.


He just installed the part. this wasn’t his fault, we approved him doing it like that. Yes, I know, stupid on our part. Going on what the service manager said about the codes “being wrong” we thought that would simplify things. Now we know better, of course.


P0722 = Output speed sensor no signal.

Someone needs to determine whether there’s no signal because the output speed sensor is faulty, or whether there is another reason the signal is not getting to the computer.

The code doesn’t say “replace the output speed sensor.”

Testing the signal from the output speed sensor would seem like a good place to start.


Unfortunately, the Chevy Aveo is not exactly GM’s finest work. It is merely a slightly reworked Daewoo that GM acquired the rights to when they bought the assets of the bankrupt Daewoo Corp of Korea. All-in-all, these cars really have nothing to recommend them.

If you keep the car, the next step in maintenance will be replacing the timing belt.
IIRC, the maintenance schedule for these cars calls for timing belt replacment to be done at 60k miles. However, poor engineering has resulted in early timing belt failure on many of these cars. Do you really want to have to spend…maybe $400 or $500 on this maintenance in the near future?

Personally, I would try to cut my losses at this point, and simply trade it in on something else. Even a used car from another manufacturer (Honda, Toyota, Nissan, Subaru, Ford) would likely be more reliable, as long as it has been properly maintained. Do not buy a used car unless you can see documentation of its maintenance and can compare this maintenance to the mfr’s maintenance schedule.


And we wonder why GM failed. We wonder why their stock dropped to $.27 a share (March 2009).

No offense intended, but perhaps instead of having the independent shop install the part you should have had them do their own diagnosis of the problem. Perhaps that’s your next best step.

I don’t know, but I suspect that your VIN number tripped a flag telling the tech that the model year and/or year of manufacture indentified by the paperwork were inconsistant with the year of manufacture code encapsulated in the VIN number. You warranty is based on the date of purchase, so I wouldn’t lose any sleep over this. You can, if you’d like, look at the year of manufacture on the door jam placard and see for your own curiosity when the actual year of manufacture was.


As mcp said - someone needs to test the whole circuit for the OSS. If it isn’t getting proper voltage or sending signal back then the system won’t work. I.e. it may just be a wiring problem.


My only advice is that if you replace the car, shop for a dealer as you would for the car. This is particularly important on a new vehicle where warranty work may be needed. I bought a Ford Windstar about 10 years ago from a small town dealer in a neighboring county. The service department was very accomodating. Unfortunately, when I was ready to buy another minivan, Ford quit making them.

A letter to the customer relations department at GM from a lawyer outlining the problem may bring results.


The OSS is a gear driven sensor. It generates its own signal.

The voltage value will change from approximately 0 to 12 to 0 volts per pulse. There will be 4 pulses per revolution. The sensor can be checked with a DVOM, if it doesn’t have the required pulses it has to be replaced. If it does then the harness can be checked to see if there is an open somewhere in a wire.