I am considering buying a 2000 4.2, however the buyer claims it is in LIMP MODE with a check engine code that reads "incorrect gear ratio monitoring."

Is this a sensor issue or a mechanical issue? Has anyone dealt with it before, and what are the potential parts costs?

Thanks in advance.

 

That is more of a mechanical issue than electronic issue. The 4.2 40V had the ZF 5HP24FLA and there have been reports (although this has also been disputed) that the 300HP 4.2 40V are too powerful for this tranny. This vehicle may have had it's tranny rebuild or serviced incorrectly. There are a number of reasons as to why the C5 A6 is on Limp Mode but "Incorrect Gear Ratio Monitoring" is something serious. I'd have it diagnosed by an independent dealer and taken to a tranny shop before making a deposit.

 

This could be a positioning sensor, but it could also be a torque converter or any number of different mechanical issues. All that code means is the RPM at the output shaft is different than the expected value given the speed of the input shaft. It's the code mine threw when it sheared the weld off Clutch Hub B and in the process destroyed Clutch Drum A. $1000 in parts, not including labour or fluids which I was lucky enough to have warrantied. Labour would have been at least another $1200 - $1500 on this job.



The ZF 5HP24FLA variant of the ZF HP24A was also used in the C5 S6/RS6 and D2 Audi A8. The standard A model is still being used in the BMW X5 and many other European applications. Most of the problems with over powering this transmission come from the RS6, the power output from the NA 4.2's used in the A6, S6 and A8 are generally not enough to cause problems. However, most of these transmissions do need to be rebuilt at around 200,000km at a cost of roughly $4000 so factor that into your offer if there's no receipts for a recent rebuild.

Frankly if it's a car with a tranny in limp mode I would either deduct the cost of the rebuild from your offer and plan on doing the 6MT swap into the car instead or just walk away from this one and look for other examples. My car has had $2200 in transmission work over the last 6 weeks and $6400 in the last 18 months (less than 20,000km). The majority of that was a rebuild by the PO about 10 months before I bought it but if I'd paid it all that would be less than a 6MT swap which would make it a much more fun car to drive.

 

If you own an RS6, you pretty much have to have your tranny rebuilt at some point. I know of quite a few people on Audiworld that own a bone stock 4.2 40V and have had to have their transmissions rebuilt well before 200,000km. I know of one RS6 owner that had to have their transmission rebuilt even before 20,000 miles. Thankfully it was under warranty. From what I gather one of the best places to upgrade your ZF 5HP24FLA would be Level 10, just be prepared to spend a nut on their work.

Spending $8600 on your transmission in less than 2 years is too much, even for our cars. I wouldn't spend that kind of money unless it was an RS6 or an M5, and even then it has to balance itself out somewhere.

I can't really recommend purchasing the vehicle with any type of transmission issue. If this was a GM where all the parts are cheap and everything is easy to fix then go for it. But our cars are quite a bit more complicated. Hell, I just replaced one of my catalytic converters on the weekend and the bloody thing took me 4 hours!

 

I have owned two C5 A6 4.2s. A 2000 (which I currently own) and a 2001. On both, the trans went within six months.

On the first, I had it replaced with a rebuilt trans (approx $5000). It had 105K.

On the second, I swapped in a manual 6 speed (approx $5000). It had 167K.

The trans on these cars are crap. The manual swap transforms the car into a powerhouse. However, it is a lot of work. I had to find all the parts for the swap myself, and find a shop to do the work (i.e. Eurotech).

If you can get the car for $5000, and are ready to drop another 5000 to 8000 into it, then go for it. Otherwise, I would steer clear.

Cheers!

 

I agree. On the 2.7T cars, the main issue are the turbos. On the 4.2 40V cars, the main issue is the ZF 5HP24FLA. On the 2.8 30V cars the main issue is lack of excitement.

 

My reverse gear crapped out today - quoted for a complete rebuild... 168,000Km!

 

In my experience EVERY 4.2L will need to have it's transmission rebuilt between 150,000 and 200,000km. That includes the A6, S6, RS6 as well as the D2 A8 and S8. Same thing happens with the BMW X5 and Jag's that also use the ZF 5HP24 derivatives. It's just a fact of life and is basically excepted maintenance with these cars.

I didn't. The previous owner had it rebuilt for $4400 and I've spent just over $2200 on it in the time I've owned it.

The transmission is the weak point in every C5 4.2L A6, typically you rebuild it once and it will be good for the rest of the life of the car. That's what you accept when you choose to buy one of these cars, you also choose to accept higher maintenance and repair costs. If you want a vehicle that's cheap to maintain then buy the GM. As long as you budget for a full rebuild and tailor your purchase offer accordingly I see no problems in buying a higher mileage 4.2L that may have issues cropping up in the transmission.

 

I'm having a few issues with mine, shifting third takes a while ie shifts at 2500rpms instead of roughly 1800 RPM when driving old man style. I am truley considering 6 speed swap

 

In that case, talk to Frank at Eurotech in Etobicoke. He did my swap, and can help you out. I sourced all the parts myself when I did mine, and had them do all the work.

If you have any questions about the swap, let me know.

Cheers!