panagath

That is a good point. My 981 GT4 does not have reverse camera and TPMS is shown on the RH screen of the cluster, rather than the headunit.

Since the erisin unit does not listern to CAN commands for changing the brightness of its screen, the only feature I see that it has to do with CAN is to show when a door is open on the erisin unit, which I don't really care about.

andy2111

I've been wondering myself what might not work after cutting the cable... It may be a choice between the bright lights and some functionality

Chuck245

Only one way to know: bring the cutting pliers.

ZedZed

Besides losing the backup camera, which would be a catastrophic side-effect, the 'door open' feature seems to be intimately linked with the rather more useful radar proximity detection function. Like you, I wouldn't care about losing the door/boot open feature but I wouldn't want to lose the proximity warning feature. More importantly, neither would my wife.

The backup camera can, of course, be replaced by an aftermarket camera if cutting the CAN-L wire disables the OEM camera, since all these HUs facilitate the use of an aftermarket camera. But, on balance, I would rather live with the bright light (in our car it only seems to affect the high beam light) than lose the backup camera (which I doubt would happen here as the Cayman#s backup camera is one I fitted myself anyway.

I guess there is now only one way to find out where we go next - some brave person has to cut the wire!

Chuck245

And if something really useful is disabled by disconnecting CAN-L, Andy and Panagath can push back on Erisin and request a different fix. Unless it's the actual chips mounted on the main board that are the problem, Erisin should be able to fix the firmware. But most likely, they are trying to push first the easiest and cheapest solution for them.

Chuck245

I was thinking about the HU not getting the signal that reverse is engaged as I have an aftermarket camera. But even then, I can get the signal from the reversing light. Still, we should push back for a different fix if disconnecting CAN-L impacts such things as reverse camera and proximity sensing.

andy2111

Regarding cutting the CAN-L wire, see here and follow the post from Cayman Ed over several pages

(5) Outstanding Tech Contribution! - Replacing PCM3.1 with Erisin Android head unit DIY | Page 9 | Planet-9 Porsche Forum

The posters are trying to fix a) relay clicking with the key inserted but not turned "on'" and b) someone else wants to fix the audio hiss. Erisin advise to cut the CAN-L wire and extension harnesses are used but it doesn't fix the audio issue (which I now suspect is a ground loop problem) or the relays clicking. Actually I get the relays clicking after about 20 mins of fiddling with the radio and I am 99% sure it's because I have drained the battery as it never happens when I first start.

It's interesting to read and nobody reports that any of the canbus functionality is lost after cutting the wires - but they also don't explicitly say it's all still working either! There is also some mention of shorting the CAN wire to ground..

My quadlock extension is on the way and I will try as soon as it arrives, but that could be 1-2 weeks...

panagath

If by "radar proximity detection" you mean the stock parking sensors or the adaptive cruise control, then I do not see why the HU would affect that. They wouldn't be controlled by the headunit I would hope. But again, the GT4 has no driver assists so I wouldn't know ...

I keep pushing them a bit. I told them that these issues are getting know to the porsche groups now and they should be looking for a software update.

What is the relays-clicking issue? Yesterday when I went to check it again I got a few weird times when the cluster was turning off and on. Is that it?

ZedZed

I am pretty sure that the relay clicking is being caused by battery depletion. We are sitting in our cars for ages, configuring the settings etc. This drains the battery and then that relay clicks if the key is in the lock. I have heard this once or twice, but in normal use of the car I have never heard it again. Even if the new HU is somehow instigating it, it isn't really an issue in normal use of the car.

In that other thread there seems to be some confusion about which wire has been cut with some posters saying it is the wire to one of the rear speakers, for example. I think we need to wait and see the outcome of Andy's experiment wheen his new harness arrives before we can come to any conclusions.

The small 'black box' referred to in the supplied harness is a voltage stabliser. A lot of users back in the day reported various issues when they went into Sport Plus mode. The consensus was that Sport Plus can create a higher and/or fluctuating voltage demand and this was futzing with the unit (this was especially an issue with the Isudar style solutions). The sellers supplied this new 'black box' harness and it fixed the problem.

andy2111

The relay clicking is definitely when the battery is depleted - it takes about 20-30 mins of playing with the head unit with the key in the ingnition and then the clicking starts every 20-30 seconds

I had the battery on charge once when I was in the car playing around and it didn't click at all, even after a couple of hours, so it's definitely a low battery side effect.

Chuck245

Let me start by saying that I'm by no means an expert on CANbus but as I was curious about the recommendation by Erisin to just cut CAN-L, I did a little bit of research, and we might not need to worry about losing functionality by disconnecting CAN-L.

IF (big if) I interpret the information below correctly, CAN-L works with CAN-H to ensure integrity of the signal transmitted through the CANbus. If this is correct, disconnecting CAN-L will not change the information circulating through the CANbus between the HU and the car's components but will just remove the integrity-check mechanism.

Also, interesting that both CAN-L and CAN-H need to be "terminated" with a resistance of 120 Homs. I know by experience with other communication bus-based systems that not-terminated nodes can create all kinds of transient and weird issues across the system. Is Erisin asking us to disconnect CAN-L because it is not terminated?

A lot of speculation and again, I'm just trying to understand something that is new to me, and I can be wrong. Definitely next step is to get the quadlock extender and try to disconnect CAN-L.

BTW: I'm experiencing the same behavior about the relay clicking. Only when the batterie reaches some level of depletion.

Automotive Communication Networks, Part II CAN Bus (snapon.com)
CAN bus physical layer (picoauto.com)

andy2111

That's very interesting Chuck - in post #182 and #184 (5) Outstanding Tech Contribution! - Replacing PCM3.1 with Erisin Android head unit DIY | Page 10 | Planet-9 Porsche Forum they are saying Erisin advised connecting CAN-L to the ground wire in the "A loom"

Do you think connecting it to ground is ths same as terminating? There most be some reason for saying connect it to ground rather than just cut it and leave it as-is

And I asume when the wire is cut and there are two ends it's the "car loom end" that is connected to ground and not the "head unit end"? This could be an additional step to try when we get to test...

Chuck245

Andy, thinking alike. I was actually ready to add something to my posting about why Erisin may recommend to ground CAN-L on the "car's side".

As you state, disconnecting CAN-L means that from the car's CANbus point of view, it is not terminated. But it may be that the car's CANbus Gateway is smart enough that if it detects no changes of voltage on the CAN-L, it just ignores it. It is not unusual for bus-based communication systems to "ignore" nodes if the network manager sense that the node is not behaving correctly.

Grounding the CAN-L in place of installing a 120 Homs resistor also seems to me as a "brutal" approach but as stated, I'm no CANbus expert and hypostatizing.

I would suggest to first just disconnect CAN-L and see if the issue is solved. If yes, we should push Erisin to provide an explanation about the exact issue that is solved by disconnecting the wire. And if not solved, before to ground the wire, I would just ask Erisin for next steps.

ZedZed

I've never heard of grounding one of the CAN H or L wires before. Seems like an odd suggestion for them to make. Ground is zero resistance, so if the CAN wires need terminating with 120 Ohm resistor, the idea seems counter-intuitive. CANBUS wires are always a twisted pair, which makes them resistant to interference, so separating them isn't a great idea either.

I'm certainly no expert on CANBUS either, but based on some of the suggestions from the seller, what worries me is that neither are they.

Agreed totally. Andy has ***** of steel so he may be prepared to try these suggestions though

andy2111

Ha Ha, I am in the fortunate (but costly) position of having a spare head unit that can be used as a test mule, so happy to experiment on that!

BTW, according to eBay my canbus extender has not yet been dispatched