Will I get trouble codes when I change the ratio of the differentials?
 

I have a set of 4.10 ratio differentials that I am going to install in place of the stock 3.90 stock ratio diffs.

Two questions:

Is there a way to correct the speedometer to show an accurate reading?

Will the change cause trouble codes that result in dash warning lights that I can't get rid of or cause a failsafe limp mode?

Isn't the speed based off of the ABS rings on the axles? I think you should be good to go on the speedometer.

There should not be any need for correction to the speedometer since the speedometer is synch with a wheel sensor. The wheel sensor will still see the same wheel signal as before unless you change the diameter of the tire.

Engine speed (rpm) will be higher for a given mph by the wheel sensor, but engine speed varies depending on the gear that the trans is in.

You will need to do some more research as to if the change in the differentials will cause additional trouble codes to pop up or for the car to go into limp mode.

You should be good to go Brian.

There was a thread around a year ago where a member did the swap and no codes came up.

I agree - as long as you change both diffs, the car won't know the difference. Speedo is based on one of the rear wheel speed sensors. Only is wrong if you change the tire size to something with a different outer diameter.

Upallnight- I agree that it seems like there should be no issue with the speedometer causing a problem or reading incorrectly but can't find anything that confirms that is the case.

James- I Have done several Google searches with different key words and not located anything that helps. I used differential ratio to search here and I found two threads discussing ratio changes. There is no mention of problems but there is nothing that says it was plug and play either. One is a Green Dragon 3.0 thread and the other is a Daddy Warbucks 4.6 thread that can't be trusted. Any idea what search words might match the content of the thread you saw?

I bought both front and rear diffs and staying with stock size tires and rims, the staggered 87s rims and tires that came on a 4.6.

To add, I have read up a bit on BMW diff swaps and from what I've seen it is GTG on most BMW's of the same era like the E46 and E39. Lots of people who have done it successfully on those chassis and have posted about it.

Much harder or impossible on Mercedes of the same era as they have a sensor in the diff that ties in to the TCU and it goes nuts with a different ratio, from what I've come across.

I was lightly perusing it as a way of pepping the 3.0 but it already has the highest ratio available.

Come to think of it, there are a few threads here of 3.0 owners going to 4.4 diffs IIRC.

I seem to recall someone in JBelknap circle of friends did a 4.44 diff swap, no coding required.

I will search for the thread Brian.

Here ya go!

4.10 to 3 64 conversion on a 01 X5 3.0.