2004 E85 Z4, Australian model: Following a flat tire recently it became obvious that the runflat tire pressure warning system wasn't working, as there was no warning lamp or buzzer. After having the tire repaired and resetting the system via the dashboard button, I checked this by letting air out of each tyre in turn and driving around the block, and there were no warnings.
My specialist BMW service center (not affiliated with BMW Australia) couldn't locate any reason for the fault as there were no fault codes logged. If the run-flat warning system is malfunctioning, the dashboard indicator is supposed to light up yellow, but there is no indication and no stored fault codes.
It's important to note that this model uses a different system for detecting low pressure from many other models - I'm told that US models use the "RDC" system which detects actual tire pressure, whereas Aus models use a system that detects a different rate of wheel speed from the other wheels.
Coincidentally, just 8 days before the flat tire, I'd had a faulty wheel speed sensor replaced - the sensor that detects loss of traction. When that sensor failed, it brought up several warning lights, and all of the safety systems became inoperative. I don't know whether the same wheel speed sensor is used for loss of tire pressure, or if there are actually two different speed sensors for each wheel.
Not long prior to this, the runflat warning system was working - I know this, because I have a slow leak in one tire, and when it gets below a certain point, the system warns me - and the last time that happened was not so long before the sensor replacement.
So the timing of the two things is interesting, but the service center reckons the new wheel speed sensor can't possibly be the cause of the issue.
Thoughts, please?
I agree it does seem more than coincidental. Will give it a few days to see if anyone else has had this issue. It's a tough one to google because all the results regarding tire pressure warnings are from those who have had the warning, but none that I can find from those who haven't. If no other explanation, I'll ask the service center to re-check the installation.
I finally have an update on the situation which may assist anyone else who has the same issue - unlikely though, as it seems to be an extremely rare event!
It seems that the fact that I'd had a wheel speed sensor replaced shortly before the problem became evident was indeed a red herring - nothing more than a very unlikely coincidence.
More recently, I had a damaged Michelin runflat tyre replaced. This tyre was several years old and when it was about a year old it started to develop a bulge in the sidewall right near where it contacts the rim. I'd been keeping an eye on it over the years in case it got bigger, but it didn't seem to be; or if it was getting bigger, then it was so slow that it wasn't noticeable. But eventually the bulge developed a split. I could see fabric inside, although it was still maintaining pressure. Nonetheless, of course I had the tyre replaced before it failed catastrophically.
And what do you think happened, as soon as I drove off from the tyre place (having replaced it with a Bridgestone this time)? Yep, the tyre pressure monitoring system immediately sprang back into life, with both a buzz and a lamp!
No-one has been able to explain why a bulge in the sidewall should have caused the issue... yet the evidence suggests exactly that.
So my advice to anyone reading this who may have the same issue: check your tyres for flaws!
split Michelin.jpg
Last edited by Raleigh; 06-19-2018 at 09:50 PM.
It definitely was not the bulge in the tire,
but totally coincidence that removing/replacing the wheel,
caused your wheel speed sensor to become operational again!
The wheel speed sensor install was indeed the RED FLAG!
Last edited by MIKYZZ4; 06-16-2018 at 10:54 PM.
An interesting point! You might be right. But I think in this case that the wheel had already been removed from the car as part of the fault diagnosis. As part of that, they tested the output signals from each wheel speed sensor with an oscilloscope. They are supposed to be square waves but one signal - the same wheel as had the faulty tyre, as it happens - was outputting a 'dirty' signal. It turned out that the wheel speed sensor's connector needed reterminating, and hopes were high that this would resolve the issue! And... sure, it cleaned up the square wave nicely... but alas, it didn't fix the main issue at hand :-( Anyway, I'm going to call the service centre on Monday to ask whether they needed to remove the wheel to do all this - if the answer is no, then you may just be correct!
Yes, the keyword here is, as you rightly say, "monitored". That's how I noticed the split on the same day that it occurred, and was able to deal with it in a timely manner.
The sensor senses wheel speed/rotation by magnetic principles,
the condition of your tire rubber has no effect on the on/off operational aspect,
but only detects the changes in rotational speed of the metallic splines on the hub/axle.
Basically you had or still have corroded terminals on the electrical connections.
I would simply replace the sensor and wiring if symptoms persist .
What a coincidence. I have an 03 2.5. I had a tire go down. The red tire warning let me know it was flat. I fixed the tire and light went out. Now yellow brake light and triangle stay on all the time when they used to come on then go off. I'm in the process of cleaning sensors with contact spray.
Well guess what... I think you're absolutely correct! I checked with my service centre and they confirmed that they didn't actually need to remove the wheel to re-terminate the connections at the wheel speed sensor - so that wheel had not been off the car after all, until the tyre was changed.
I'm reckoning you're right about this too, because the one thing I hadn't done until just now is to actually deflate the tyre to check whether the system would indicate an alarm - embarrassingly, I'd pretty much just assumed that it was working now. Well, I just did that test - I let it down from 40psi to 20psi and drove for 1km (1.6 miles) which I'd have thought was plenty far enough for the system to detect the low pressure? Well, it didn't
My service centre explained that the system does a self-test on startup, and also periodically while driving. If there is a fault (which there obviously is) the result of that test ought to sound the buzzer and show the warning lamps on the dash. So there are a couple of possibilities here: maybe it's not doing the self-test; or maybe it is doing the self-test but it isn't sensing the failure. Either way, it seems the self-test is failing. But if that's the case, it may not necessarily indicate faulty wheel speed sensors (ie. could be something harder to diagnose and potentially more expensive, like the DSC computer?)
As I mentioned, they've already ascertained that all four sensors are outputting a nice clean square wave signal, but at your suggestion, they'll check more closely for corrosion!
Replacing the wheel speed sensors isn't cheap. One that failed was replaced a year ago as I mentioned in my original post, and that cost me AU$630 including labor (about US$450) so it's not something I'd do with the other three, just to see if it fixes the situation.
But I'm not quite sure what you meant at the end of your first reply "The wheel speed sensor install was indeed the RED FLAG!"?
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