825LTRGT

Sorry Dixie. I should have tested a bit more before I opened my trap.
If you drive less than 18 miles it doesn't come on at all.

The pressure in the "bomb" is still 40 psi.

The funny thing is that the message and light clear when the car is restarted. They stay off until you drive 18 miles.

It doesn't say "low tire pressure" like it did before. So it kinda works.

Dunno

Dixie_Flatline

Do you have all four in there? Hrmmm... I may make it just to play around with it. I've heard from reliable sources that it should work... maybe one of the sensors died on you? Wish I had an RFID scanner now.

825LTRGT

3 are in the PVC, one is in the left front wheel.

They all calibrated ok.

I'd still like to know what the significance of 18 miles is. It's odd that there is no problem until then.

Dixie_Flatline

Ah, is your left front tire at 40 psi as well?

My guess is the 18 miles is when the car reports diagnostic errors. Otherwise if it were continuous, the driver would be bombarded with annoying messages. Like Windows Vista when it first came out.

Dixie_Flatline

I made the PVC pipebomb and put my two rear sensors in. Used unthreaded caps on 2" diameter pipe. PVC cement and taped the sensors to a paint stir stick/wooden shim. Pumped the cylinder to roughly 35psi.

Drove around for 35 miles over two hours, making several stops at stores and stuff.

Works like a charm. No dash lights, no beeps, wouldn't have any idea that the two sensors from the rear wheels are sitting in a plastic pipe on the passenger seat.


John, I'd try letting a little air out of the pipe, maybe the system compares tire pressure across each axle, so if the right tire shows more air pressure than the left, it could trigger a sensor fault or something. If that doesn't fix it... maybe you got bum luck and a busted sensor.

Of course I'll be driving a lot more, usually about 250 miles a week, so I'll let you know if the sensors start crying foul again. But it's really nice to not hear that beep and have to clear the fault anymore.

825LTRGT

Yup, mine works great until I get on the highway and drive 18 consecutive miles without shutting the car off.

I'll try that. Maybe the tire that has the sensor builds up pressure and throws the system off.

Dixie_Flatline

Ah, yeah, haven't done 18 consecutive miles yet.


I know that the early BMW tpms systems were a comparative system that would only go off if there was a difference in pressure between wheels on the same axle. So if both rear tires deflated at the same rate, there wouldn't be an alarm. If the right rear tire deflated and the left rear didn't, then the system would go off. Maybe it's in the system diagnostics that if there's a differential.. and heat will raise pressure, that it may think something is wrong with the sensor. Just a guess.

Good luck! (I'm hoping it sticks for me too!)

cdynaco

So guys, how's it working??

825LTRGT

Still works fine until I hit the 18th mile. Then the "Tire pressure sensor fault" comes up and the light comes on. Reset clears the message but the light stays on after flashing for about a mile. Turn the car off and restart and the process starts all over again.

No clue how to fix this yet.

Dixie_Flatline

I don't think I've driven even 10 consecutive miles without restarting the car, but I've put on 150 or so since I made the pipe. Nary a light, signal or message that needs resetting. Will definitely post here if that changes though. Or I drive further than 20 miles in one go.

825LTRGT

I've driven over 500 mi without a problem until I drive more than 18 consecutive miles.

So, I'd say it works but some tweaks needed.

Dixie_Flatline

Ok, went out of my way to drive a single drive today. I got the flash and beep saying TPMS Sensor Fault at mile 12.5. My guess is it's not continuous mileage, but continuous drive time.

Before I made these I did hear that the sensors have the ability to transmit motion indication via velocity sensor or inclinometer or whatever, but people assumed it wasn't being used. My guess is it is being used, just only on intervals.

May be one of those things I'll have to just live with. So far, not terrible though and I'm still definitely glad I made it.

825LTRGT

Tested on the way home from work.

Went 14 miles to a gas station and filled up. No light/message.

Drove another 17 to get home and no light or error message.

Total of 31 miles.


Later, went to do some xmas shopping and got the light at 18.5.

Started the car about 10 min later and got the light and message.

Went to another place and let it sit for an hour or so, no light until 18 miles.

So there must be some sort of keep alive message or something.