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YOUR RESEARCHBest Practice for Can bus tap?
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Replace but i'm not sure
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I've found something that MIGHT be related to the torque converter status (x0, x1, x2, x4, x22, x24) that definitely changes but I'm not sure
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I got all set up to start capturing CAN traffic on my 2001 C4 Cab w/Tip over the ODB2 connector, but was befuddled that I didn't see any traffic. As many know, including me now, those pins aren't connected on this model and others. My Chevy Traverse was very verbose, however. That proved the equipment.
So now, I need to figure out the best place and method of inserting a 3 pin connector that I can go to in the future without having to tear stuff up every time.
There's a connector that I already have exposed that is in the driver's side, passenger area near the outside. I could also either trace those wires where they hit the dash area. Or, pull the instrument cluster. Or run wires back from the PSM. Or, tap off at the Tip or DME.
The fact that they terminate the can bus in 120 ohms is concerning, however. That is intended to help eliminate reflections of the signals on those lines. Transmission lines 101.
Hence this post: what is a tried and true method to tap in without inducing issues?
I found an "easy" place to tap in at the steering angle sensor. It has all the signals and is just a bundle of 4 wires. Being a contortionist would have been helpful, though.
The results of this experiment will be very interesting. Earlier cars didn't have PSM and therefore no steering angle sensor. The csnbus was simply point to point from the DME to the instrument cluster.
On tiptronic cars there is another point to point canbus from the DME to the gearbox.
Diagnostics are done separately on Kline with the alarm module under the seat acting as gateway.
The K-Line diagnostics bog down with live data on my car. The CAN bus tap spit put 500k frames in 5-10 minutes. A lot to dog through, but on the right track.
Perhaps you can utilise AI such as Claude or ChatGPT to write a canbus log frame decoder that runs in near real time?
I used this method recently to write offline decoders for the EEPROM dumps from the ME7.8 Engine ECU and also the M534 alarm module.
I watched a video of a guy doing that. Very impressive. I haven't programmed in a while, and haven't used AI for that purpose yet, but will need to explore that.
My problem is that the K line seems to get overloaded with some data, like the wheel sensors, over 30 MPH. Since tapping into the CAN bus, I've been able to see the wheel sensor data at above 40 and probably as high as I want to go.
I want to be able to see engine rpm, Tiptronic input speed, Tiptronic output speed, and anything else I can see relative to requested gear, actual gear, torque converter lockup, trans. temperature, etc.
As it stands, I have an oscilloscope tied to all the transmission valve / regulator drive lines. So, if I can marry that with the CAN data, I'm hoping I can figure out what's causing it to go into limp mode.
It tells me that one or both of the front wheel sensors are implausible, but it also says gear monitoring is implausible and there's a stall speed error.
Something is clearly slipping somewhere, but the error codes don't tell me exactly what.
Ideally, I need a full DBC for the 996.1 including the 2001 Carrera 4 model
Current state:
I've made progress with the help of Mr Google and
@MisterCorn
. I've definitely found the shifter status (PRNDM) and gear as well as the limp mode indicator (0,F). I've found something that behaves like shift status (0,1,2 = Stable, Upshift, Downshift), but it doesn't always make sense. I've found something that MIGHT be related to the torque converter status (x0, x1, x2, x4, x22, x24) that definitely changes but I'm not sure
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