[vtsng]

Was planning for a weekend getaway with my wife for her birthday but the highways have a winter tire enforcement law in effect. Being the law abiding citizen that I am, I put in a set of winter wheels and after the first 10km, errors started popping up in the following order:

1) Flat Tire Warning
2) Flat Tire Monitor Inactive - System unable to monitor tire pressure. Consult service center.
3) DSC and xDrive malfunction - Chassis stabilization and traction reduced. Drive moderately. Consult nearest service centre.

My original wheels are BMW style 308 (8x18 square on 245/50/18 all around)
My recently installed winter wheels are BMW style 161 (8x17 square on same brand and style 225/45/17 all around with 10/32 tread on all tires)

I am under the impression that Canadian vehicles do not use TPMS (my OEM wheels have the rubber valve stems) and the vehicle measures the wheel's rotational speed to detect a difference in tire pressure. Am I right in assuming that so long as all 4 wheels are the same size and same tread pattern/ wear, there shouldn't be any damage to the AWD system?

When I start the car, the Flat Tire Monitor (FTM) is active and all tires appear green on idrive. But almost instantly when I start moving forward, the FTM becomes inactive, immediately followed by the DSC and xDrive malfunction. I've tried resetting the Flat Tire Monitor (FTM) before moving the car, but once again as soon as I move forward after the reset the errors come up again.

Shouldn't the ABS system be able to calibrate the FTM so that I can run these new wheels? Isn't that what the reset function is for? Or is there a more serious problem here?

I driven another 100km @ speeds of up to 120km/h with the errors on the dash but without any ill effect. But these messages are still keeping me up at night. Last thing I want is to be stranded away from home on my wife's birthday. Would really appreciate any opinions here!

[ejw2011]

The tire size should be 225/60r17. Diameter is 25 vs 27.8,
Circumference is 78.4 vs 86.8, revs/mile is 832 vs 752.
The big differences from 17 to 18" causes these errors if you don't get the correct tire specs. 225/60r17 will be in allowable specs. Check out tiresize.com calculator comparing the 245/50r18 vs 225/45r17 look

[doru]

I thought OEM specs for X3 tires (and wheels) are as follows:
205 / 65 / 17 ET 32
225 / 60 / 17 ET 32
245 / 55 / 17 ET 43
245 / 50 / 18 ET 43
245 / 45 / 19 ET 38
275 / 40 / 19 ET 48 (rear - staggered setup)
245 / 40 / 20 ET 38
275 / 35 / 20 ET 51 (rear - staggered setup)

However, not sure if you double-checked the tire pressure to be the same for all wheels, then before driving, you should reset the TPMS on the dash.
Could be that the vehicle (computer) knows what the speed should be according to wheel revs and compare to actual speed - but I'm not 100% sure it works like that (i.e. comparing theoretical speed stored in ECU/TPMS at given revs with actual speed given by revs of speed sensors, etc).
Could also be that coincidental the TPMS monitor system sensor is faulty - easy to change (no dealer - it will "fine" you) - one or 2 screws under rear passenger wheel I believe. Or one or more TPMS sensors in the wheels are bad.

Basically the TPMS monitors if there are any differences in the tire rolling diameters, so if one tire is more or less inflated it will trigger the error. This is why I am not 100% sure if it also has a "stored theoretical" speed for given rpm of tires.

This here is the control unit and as I said, could be under the car on the subframe close to one of the rear wheels, but BMW might hide it in some other odd places like inside the liner of one of rear wheel wells or in the battery compartiment, etc.
Also, if humidity hit the RDC module somehow, you can have those or more x-mas lights - see this but easily fixable. The RDC module if bad, there are for sale on e-bay at reasonable prices.

0.02

[Tjalle]

I take it you don´t have TPMS Tire Pressure Monitoring System via pressure sensors, but the ABS based indicative system, which counts wheelspeed.

System does not count real wheelspeed, but difference between rotational speed on wheels. i.e. you can change wheelsize - if on all four.

After change of wheels, you need to calibrate - with correct tirepressure.

My reading is that one of the ABS sensors, does not send signal to system OR system is inactive.

IF I am right, you are in no real trouble.

[vtsng]

Originally Posted by ejw2011

The tire size should be 225/60r17. Diameter is 25 vs 27.8,
Circumference is 78.4 vs 86.8, revs/mile is 832 vs 752.
The big differences from 17 to 18" causes these errors if you don't get the correct tire specs. 225/60r17 will be in allowable specs. Check out tiresize.com calculator comparing the 245/50r18 vs 225/45r17 look

Thanks this information is very helpful. I'll definitely keep that in mind when I get new winter tires!

[vtsng]

Originally Posted by doru

I thought OEM specs for X3 tires (and wheels) are as follows:
205 / 65 / 17 ET 32
225 / 60 / 17 ET 32
245 / 55 / 17 ET 43
245 / 50 / 18 ET 43
245 / 45 / 19 ET 38
275 / 40 / 19 ET 48 (rear - staggered setup)
245 / 40 / 20 ET 38
275 / 35 / 20 ET 51 (rear - staggered setup)

However, not sure if you double-checked the tire pressure to be the same for all wheels, then before driving, you should reset the TPMS on the dash.
Could be that the vehicle (computer) knows what the speed should be according to wheel revs and compare to actual speed - but I'm not 100% sure it works like that (i.e. comparing theoretical speed stored in ECU/TPMS at given revs with actual speed given by revs of speed sensors, etc).
Could also be that coincidental the TPMS monitor system sensor is faulty - easy to change (no dealer - it will "fine" you) - one or 2 screws under rear passenger wheel I believe. Or one or more TPMS sensors in the wheels are bad.

Basically the TPMS monitors if there are any differences in the tire rolling diameters, so if one tire is more or less inflated it will trigger the error. This is why I am not 100% sure if it also has a "stored theoretical" speed for given rpm of tires.

This here is the control unit and as I said, could be under the car on the subframe close to one of the rear wheels, but BMW might hide it in some other odd places like inside the liner of one of rear wheel wells or in the battery compartiment, etc.
Also, if humidity hit the RDC module somehow, you can have those or more x-mas lights - see this but easily fixable. The RDC module if bad, there are for sale on e-bay at reasonable prices.

0.02

Unfortunately my car is Canadian so it doesn't use TPMS, rather it uses the ABS system to detect rotational speed. For some reason I'm unable to reset it no matter how many times I've tried...

[vtsng]

Originally Posted by Tjalle

I take it you don´t have TPMS Tire Pressure Monitoring System via pressure sensors, but the ABS based indicative system, which counts wheelspeed.

System does not count real wheelspeed, but difference between rotational speed on wheels. i.e. you can change wheelsize - if on all four.

After change of wheels, you need to calibrate - with correct tirepressure.

My reading is that one of the ABS sensors, does not send signal to system OR system is inactive.

IF I am right, you are in no real trouble.

You hit it right on the nail, my car is Canadian, it does not have TPMS. Rather it has what BMW calls a "Flat Tire Monitor (FTM)" which in other words is the ABS based system.

I've tried calibrating with the "reset" feature on the FTM but it still doesn't seem to have any affect. The moment I move forward after resetting, the "Flat Tire Monitor Inactive" and "DSC and Chassis Malfunctions" all pop up again.

I have the same thought as you in that the ABS sensor is just panicking because of the sudden change in wheel size from 18" 245/50/18 to 17" 225/45/17, which in turn triggers the malfunctions. But theoretically speaking, everything seems to be ok as you say and shouldn't cause any damage. I'm just not quite sure why I can't reset and calibrate to the new wheels...

[Merlin82]

Maybe check the ABS sensors. I had zero problem with mine when i swapped from my winters to summers in the spring. And my winters are the 18's and summers are 19's. Now im guessing the rotation is about the same between both of mine, but i reset it no problem and never saw a single light come on. Maybe an ABS sensor got hit or something while changing them.

[doru]

Wheel speed sensors can also become clogged/loaded with brake dust & rotor shaving and it will throw out the readings. On my old e39 I had an ABS/DSC etc. malfunction because of that. Cleaning them solved the issue. Not sure how the wheel speed sensors are attache to newer BMW's, probably the same as on the old ones, and if that's the case, one should be careful when attempting to pull them out. They are held in by one screw, but all that road crud gets lodged in where the wheels speed sensor sits (in the hub) and if you pry too hard on that plastic flange that holds the tightening screw, you can break it off. Not only you need a new sensor, but the leftover is very hard to pull out. Need some WD40 or other thin lube, and patience. And work it very gently. At first it won't budge. Hopefully these newer models BMW have a slightly different design...