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Post by golf75retrofit on Apr 14, 2024 15:52:32 GMT
I installed direct TPMS a few months back using the famouse Spanish guide, however I get the following fault: Trouble codes: U012700 - Lost Communication With Tire Pressure Monitor Module Intermittent Date: 2024-04-14 15:18:20 Mileage: 119898 km Priority: 2 Malfunction frequency counter: 2 Unlearning counter: 250 Supply voltage, terminal 30: 12.9 V Normally this would happen when using an ignition switched +12v supply, but it's wired to a fuse which provides continuous +12v, and I've verified there's constant supply at the unit yet the error reappears every time the ingition is cycled. I've attached a full scan Any ideas? Attachments:history 4.txt (17.27 KB)
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Post by dv52 (Australia) on Apr 14, 2024 22:24:03 GMT
hmm.............. I guess that your SCAN must have been made after you cleared the fault BUT before the ignition was cycled - because the 65 Tire Pressure module is fault free in your SCAN!!
So, the error reports that this fault is "intermittent" - which makes diagnostics tricky!
Generally this type of fault points to a problem which is physical. Normally, the cause is with the power-supply pins/wires (including earth connection), or the CAN high/low pins/wires. I suggest that you grab a multi-meter and check continuity on the respective pins/wires (back to where the wire terminations were made to the factory loom on the car)
Don
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Post by golf75retrofit on Apr 15, 2024 5:22:13 GMT
Yes the fault was cleared and the scan taken before I cycled the ignition again.
The fault is intermittent (although regular and with a known trigger event essentially) appears as green (passive) each time and not static.
Given the unit works and communicates when the car is on, could it really still be a bad connection?
I know the pins aren't in the best of shape at the TPMS module connector as they've been removed a few too many times in the past.
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Post by golf75retrofit on Apr 15, 2024 20:15:30 GMT
So I've checked the wiring and can't find anything obviously wrong.
The device is getting constant +12v power, ground seems fine.
The can lines have approx 1.8 and 2.2v with a slight oscillation. I have however noted that the CAN lines seem to go to ground a short while after the vehicle is turned off and immediately if the vehicle is locked.
I've also noticed that if I cycle the ignition immediately I don't get the fault, it appears as a static fault approximately 1 second after turning off the ignition and becomes passive once the ignition is turned on again. The fault timing appears to coincide with a noticeable click/clunk from under the dash when turning the car off.
Should that CAN BUS power down after turning off the ignition?
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Post by dv52 (Australia) on Apr 15, 2024 22:51:18 GMT
hmm.......... so, without making this reply a master-class - maybe we should go back to basics and discuss the fundamentals of how a CAN bus works on a mk7/mk7.5?
Your car has 6 x CAN busses arranged in a type of hub-and-spoke pattern - below is a very simplified schematic of the wiring arrangement for one of these CAN buses: As you will be aware, the high-speed communication spine on a CAN bus has 2 x wires (CAN high and CAN low). In the diagram, a "Node" is a module in OBD11 speak. Notice that each module on a CAN bus is connected "in parallel" with its neighbor modules. The 2 x 120 ohm resistors are physically located inside a pair of modules and their purpose is to suppress communication reflections from the CAN signal
Also notice that the diagram is free of any power-supply wires. Of course the modules themselves are connected to the car's battery to power the internal circuits - but from a CAN comms perspective, the CAN High/Low voltages on the 2 x wires float outside the +12V rail and the car-earth. When you installed the TPMS module to this car, electrically you added the module "in parallel" with the other factory modules on the Extended CAN bus.
OK, one more diagram - below is the voltage patterns for the CAN signal (these voltages are measured with-respect-to the battery negative, being the car-earth):
As shown, the voltage on the CAN High wire will oscillate from 2.5V to 3.5V and on the CAN Low wire, the voltage ranges from 2.5V to 1.5V. These pulses are high speed and the quantity of pulses vary greatly with time- so the correct measurement method requires an oscilloscope. However, with a multi-meter, the voltages should be about 2.6V on the CAN High wire and about 2.4V on the CAN Low wires (again, this is wrt the car-earth). This said, not all multi-meters are created equal and "domestic" multi-meters are often (always?) prone to inaccurate readings.
Lesson-over!!!
So, the TPMS module has only 4 x wires - which means that there ain't much to go wrong on the loom!
Plus, if you have understood my diagrams above, it will be clear that if there was a short between the CAN High and CAN low wires, the entire Extended CAN bus would fail. Since your SCAN doesn't include faults on the other modules on this bus - it's reasonable to conclude that this type of fault is NOT the cause of the problem! Or, said another way - the presence of ONLY one faulty module on your SCAN means that if this is a CAN wire problem - the cause is almost certainly a break in the CAN wires to the new module.
Of course, the other possible cause of the fault could be the power-supply! And since you identify in your last post that the module connector is not in "the best of shape" - another strong possibility could be the soldered internal pin connections inside the module!
With regard to your specific question - yes, to ensure that the battery voltage is not depleted, the entire CAN network on this car sleeps when the ignition is turned-OFF.
So, bottom-line: The simplicity of the 4 x pin connector on this module strongly suggests that this problem is physical. Intermittent faults are notoriously difficult to find - but the facts as described above still point to the wiring, or pin connector on the TPMS module>
Don
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Post by golf75retrofit on Apr 16, 2024 5:18:50 GMT
Thanks Don,
Always useful to go back to basics, I get what you mean about the bus being fine otherwise I'd get similar errors from everything else on that bus.
I measured the voltages on the CAN lines both at the TPMS connector and at the plug in the LH footwell with the TPMS disconnected and they were the same, so think the CAN wiring is fine.
I'll try changing the pins on the connector just because I can, it's the only connection that appears suspect at the moment.
After that I guess it could be a faulty module, the problem being finding a known good module that's already parameterised to test against.
The bit that got me thinking was how it's the gateway complaining it's lost communication when the TPMS module appears to be still powered, and all the connections are fine when the car is switched on. Was the gateway expecting to see messages when it shouldn't be (eg could it be a coding or adaption error with the gateway)? You're far more experienced than me, but that's where the logic in my head went.
Gareth
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Post by dv52 (Australia) on Apr 16, 2024 23:27:01 GMT
The bit that got me thinking was how it's the gateway complaining it's lost communication when the TPMS module appears to be still powered, and all the connections are fine when the car is switched on. Was the gateway expecting to see messages when it shouldn't be (eg could it be a coding or adaption error with the gateway)? Gareth: Excellent question!!!
The behavior of the Gateway module is entirely normal and I would be surprised if it wasn't complaining!! To explain why - again, lets go back to basics. Below is a "topology" diagram showing the 6 x CAN buses on a MQB platform car: Notes: - Ignore the LIN data bus for this discussion. LIN is NOT a CAN bus - it's a low-speed, single-wire comms protocol that is used for simple peripherals
- J533 is the official name in VW wiring diagrams for the module that OBD11 calls the Gateway module
Remember that I said in my last reply that "your car has 6 x CAN busses arranged in a type of hub-and-spoke pattern". Hopefully you can see this topology in the diagram above. And more importantly, hopefully you can see how the Gateway module is the central module directing activities across the various CAN buses. So, you can think about the Gateway module as being like the "Fat Controller" of Tomas-The-Tank-Engine fame!
On a healthy CAN network, the Gateway module is in constant dialogue with ALL modules that have been registered in the Gateway Installation List (GIL). You will be familiar with the GIL because you would have added the 65 module to the GIL as part of the coding changes for the TPMS retrofit project All CAN bus systems in the Golf mk7/mk7.5 have a transmission speed of 500,000 Bits per second (this means that each Bit is just 2 x microseconds long!!) and the Gateway module is responsible for catching and recording any failures by any GIL registered module to properly respond to messages sent over the CAN comms spine. Again, the CAN speed is 500 KBits/sec!
When faults/errors are recorded, the Gateway module also captures information about the prevailing electrical conditions on the car. This is called "Freeze-frame" data and it's the information that you included in your first post. The gateway module also makes decisions about the nature of the fault - like "intermittent, "confirmed", "static" etc. - these categories are defined in the ISO Standard. And finally, once an error is recorded, it will remain in the module's fault memory until it's cleared So and without intending any offense, whilst you may well have used a multi-meter to ascertain the integrity of the 4 x wires at the TPMS connector- the Gateway module uses an entirely different (and much-faster/more-accurate) system for diagnosing the health of the module!! Hope this makes sense!
Don
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