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Wanted to create a new thread specifically to present some interesting data from the TPMS sensors, and why it's not always easy to troubleshoot. I bought my 2012 XKR about 2 months ago, and I've had TPMS errors come up on the dash intermittently. My first attempts to resolve the error were basic, and futile... pressurize the tires at a tire shop in case my air gauge at home was wrong (it was accurate)... try to have the tire shop read codes to see if there was anything wrong with the module (There were no codes), pull the battery terminals, de-energize the system, and hook everything back up (Battery is new Feb 2019, and has no degradation).
Well, my iCarSoft 2.0 module came in the mail a few weeks ago, and I could never catch the warning light in time to plug in the module and see if there were any codes showing up... the error would come and go very quickly, or I'd be on the highway (or driving anywhere really) and couldn't take my eyes off the road to fiddle with plugging in the reader... etc. So, today I decided to plug the module into the car and record the TPMS sensor data on my way to work. Luckily (I guess), the warning light popped up on the dash a few times during my commute. So, I saved the file, and organized the data in Excel to chart it. Unfortunately, the data is not organized in a way that's easy to graph... so you have to manually filter through it all and organize it in a way that Excel can use.
Not only is pressure data read, but temperature and acceleration. I am not sure what the values correspond to... since it's~90*F (~32*C) outside, the temperature data was -50F when the sensor dropped off connectivitiy, and was around 40-50*F when connected. Acceleration was measured in ounces (0.00 oz when lost connectivity, and ~3.00-4.00 oz when connected)
See the attached Excel workbook for raw data.
Here are the results:
A few interesting things to note...
1) The sensors are all reading a strong signal when read via the discount tire TPMS reader.
2) It was interesting to see that right after inflating each tire to 36+-1psi (confirmed numbers), the sensors all read ~50-53psi when connected. So they are ALL reading ~15psi too high.
3) I was not able to have the discount tire rep stand by the car and wait for the warning light to come on. I was hoping to catch it to ensure that the sensors were still sending data, confirming that the module is causing the error
4) Even with this data, there are no codes showing up on my code reader
5) It seems that most of the time, all 4 sensors stop being read simultaneously... this points to a bad module, not a bad sensor... or a CRAZY (impossible) coincidence.
6) When the sensor stops being read, the module reports back atmospheric pressure (14.51 psi)
7) When the module looses connection to the sensor... it takes more than 1 'read cycle' for the error to show up... even though the graph shows this many drop-offs, the dash warning light only occurred at the beginning, and towards the end of recording.
Given that I have a good battery, and the sensors are likely good, I suspect that the module will need to be reprogrammed. Before I bought the car, the seller had the front bumper painted. He never made a comment that the painter saw damaged wiring on the TPMS module. I'd like to think that since the bumper has been removed and re-installed just before delivery, that a re-program will solve the warning light.
Can anyone comment on their thoughts to the cause of this, if you have a different hypothesis than what I've presented?
Thanks very much! Hope this helps someone in the future.
Last edited by TraxtarXKR; 08-09-2019 at 03:24 PM.
When the bumper was removed, and then re-installed, they may have damaged the wiring harness that runs behind the bumper.
Its a known problem that the harness can get pinched in there, wear through the insulation, and cause various problems.
I'd start by checking that harness, can usually be seen from right front wheel well, if you pull back the wheel well liner.
Search this forum, you'll see others that have had problems there.
When the bumper was removed, and then re-installed, they may have damaged the wiring harness that runs behind the bumper.
Its a known problem that the harness can get pinched in there, wear through the insulation, and cause various problems.
I'd start by checking that harness, can usually be seen from right front wheel well, if you pull back the wheel well liner.
Search this forum, you'll see others that have had problems there.
I can't argue with the logic behind looking at the module first before going for a reprogram. I'll attempt that first and hopefully find something a soldering iron and heat shrink can resolve.
What is the age of the tyres? You can find it on the sidewall as 'DOT XX/XX' representing the week/year the tyres were manufactured. This may be a clue to the issue with random TPMS warnings as the wheel sensors have lithium-ion batteries that fail after five or six years causing intermittent warning on the instrument cluster. If the tyres are over five years old they should be replaced along with the TPMS wheel sensors.
The readings you are getting are the absolute pressures (atmospheric pressure + gauge pressure). That's where the extra ~15 PSI are coming from. You can just subtract that value from all your readings to get the gauge pressures.
As for temp, if the module uses ambient temp, check the 'outside temp' readings on touchscreen. When its around 93 deg F outside, the display on my car shows temps around 101 deg F. That may explain the high readings - assuming the module uses the ambient temp sensor.
I remember seeing a thread somewhere where they re-installed a bumper and pinched a harness causing the TPMS to act funny. May want to take the bumper off and look into it.
The readings you are getting are the absolute pressures (atmospheric pressure + gauge pressure). That's where the extra ~15 PSI are coming from. You can just subtract that value from all your readings to get the gauge pressures.
As for temp, if the module uses ambient temp, check the 'outside temp' readings on touchscreen. When its around 93 deg F outside, the display on my car shows temps around 101 deg F. That may explain the high readings - assuming the module uses the ambient temp sensor.
I remember seeing a thread somewhere where they re-installed a bumper and pinched a harness causing the TPMS to act funny. May want to take the bumper off and look into it.
Good luck and let us know how you make out.
Tires are January 2019.
Regarding absolute pressure... Of course... how silly of me to not realize that. Sigh...
The temp is still a strange one... outside temps are at 98*F now. I can't explain whey the temp data from the sensors is reading closer to 50*F
Also important to note regarding pinched wiring in the bumper... my front parking sensors work perfectly. I have read that troubles with that harness from the TPMS sensor will also cause the parking sensors to malfunction... not sure if that is ALWAYS the case, or only in certain instances. I'm sure it also depends which wires in the harness (if it IS the same harness) get pinched.
Will report back when I get a chance to remove the bumper.
Will report back when I get a chance to remove the bumper.
You may not have to remove the bumper, just look from various angles from the back side, above, below, wheel well, etc.
I can see mine, and can tell its not in trouble of being pinched.
But in your case, pinching could have occurred before the remove/re-install too, and so even if the harness is in plain sight, you might not see physical damage without removing the bumper to get a closer look.
Well, that was a bunch of worthless babbling..., never mind, carry on, ignore the doofus...
When I first got my XKR about 6 years ago, I often got tire sensor warnings, I could get them to disappear if I inflated the tires to 40psi, and I could bleed them down a little lower from there. I have since kept them near 40psi, and haven't had an issue in years. (now watch, I'll get one now that I've said it).
No problem with my 2012 . 2nd set of tires and orign. sensors. I have an Altel sensor reader and check tires monthly. Gives me pressure , temp. and battery status of the sensors. 25K miles.
No problem with my 2012 . 2nd set of tires and orign. sensors. I have an Altel sensor reader and check tires monthly. Gives me pressure , temp. and battery status of the sensors. 25K miles.
So what temps and pressures does you reader show? Similar to my results? Is it strange to anyone else, that despite the graphed readings and disconnecting pairing, I'm not getting any error codes from the TPM system?
Ok, for my own info.... how would a person OR a device calibrate to Zero Absolute Pressure? Is their lab in orbit? Was the supposed 29.92 calculated into the 'zero' figure?
Ok, for my own info.... how would a person OR a device calibrate to Zero Absolute Pressure? Is their lab in orbit? Was the supposed 29.92 calculated into the 'zero' figure?
I'm not following... You would typically not calibrate a device to 0.0psi absolute pressure unless it was designed to measure vacuum.
When we calibrate test equipment with a 3rd party NIST lab, they typically use that device to measure a series of known pressures. As long as the device measures accurately within its set tolerance range, it can be used for product verification testing and publishable (or internally used) test result data.
If a company like UL were to sign off on your product, and did an audit of your test data, they would want to see calibration sheets and look at the dates to ensure the device was "in Cal" while the test was conducted.
The readings you are getting are the absolute pressures (atmospheric pressure + gauge pressure). That's where the extra ~15 PSI are coming from. You can just subtract that value from all your readings to get the gauge pressures......................................
Originally Posted by TraxtarXKR
I'm not following... You would typically not calibrate a device to 0.0psi absolute pressure unless it was designed to measure vacuum.
When we calibrate test equipment with a 3rd party NIST lab, they typically use that device to measure a series of known pressures. As long as the device measures accurately within its set tolerance range, it can be used for product verification testing and publishable (or internally used) test result data.
If a company like UL were to sign off on your product, and did an audit of your test data, they would want to see calibration sheets and look at the dates to ensure the device was "in Cal" while the test was conducted.
Now, what is the significance of 29.92?
29.92 inches of mercury, which is about 15 psi. Referenced by gkubrak.
Absolute pressure = zero pressure from anywhere, including atmospheric, most close to zero in space.
I just don't understand how a TPMS sensor would be calibrated to include atmospheric pressure in its readings.
29.92 inches of mercury, which is about 15 psi. Referenced by gkubrak.
Absolute pressure = zero pressure from anywhere, including atmospheric, most close to zero in space.
I just don't understand how a TPMS sensor would be calibrated to include atmospheric pressure in its readings.
Remember that the module's reported values default to 14.92psi when disconnected from the sensor. It probably uses that value as a placeholder. This could be a function of the sensor, or the module... But probably the module since the sensor stops talking to it.
Measurement processes that cannot dip below atmospheric pressure are typically measured using gauge pressure. Tire pressure, for example, uses a gauge reference because we want to know how much more air is in it than what is already in the atmosphere around it. A flat tire has 0 gauge pressure because its internal pressure is equivalent to atmospheric pressure.
It's very possible that the system is not designed to see negative numbers, and by measuring absolute pressure with a default atmospheric pressure it ensures the module will always report a positive value.
I think you guys are over thinking this a bit. My sensor tester just reads the same as gauge pressures. Simple enough.
Sure, the tester shows gauge pressure. That makes sense. The absolute values are coming from the module side of things, as that's what's being monitored by the diagnostic tool.
The point of the thread was to show how the sensors all loose connectivity to the module almost simultaneously, to present the data in an easy to digest format, and also to discuss the data that the system uses to indicate aTPMS fault.
I personally was not aware of the differences between iTPMS and dTPMS, and couldn't answer why the system was reporting absolute pressure values. It's mostly just an interesting fact to add to our knowledge base.
Once we determine a solution to this problem, folks going forward will have another point of reference to use when doing at-home diagnostics. That's why we do what we do.
08-09-2019, 03:18 PM
Another TPMS thread... with sensor data!
