Hi all,

I have a strange issue with the SLM I have added on my 2008 cup :

* I first connected it to the dash CAN last winter without any resistor and baboom ! it worked like a charm for the first part of the season.

* Then I had my ECU nightmare that lasted so long... After having changed the ECU, the car was fine, but no SLM anymore.

* Tested with another one, just in case : Nothing

* Read the Motec forums, added a 100 ohm resistor on the CAN wires, SLM side : Nothing

* In the Dash manager - Communication, I see a "slave device" on CAN 6 which should be the SLM.

Would anyone have any advice ?

 

Geoffrey is Motec guru. he's on these threads somewhere.

 

I had a similar issue and it turned out to be the ECU bridge I was using to send data to an AIM Smarty Cam. I did try the resistor during my trouble chasing and it had no effect. I replaced the defective bridge and the SLM worked again.

 

Very interesting !

FYI, the informations received by the dash from the ECU via CAN are working ok.

What is this bridge and where may I find it, please ?

AFAIK, the Dash and SLM are directly connected on a CAN bus that seems to be directly connected to the ECU too.

 

Just beside the ECU, check for a pigtail about 8" long with a 4 or 5 pin Autosport connector. See if there is anything plugged in to that connector.

 

I think you need first to understand the design of the CAN bus before you attach anything to it. The 08 has a single 100ohm terminating resistor in the wire harness at the dash, and then the MS 3.1 ECU has an internal 100ohm terminating resistor inside. YOU CANNOT ADD ADDITIONAL TERMINATING RESISTORS TO THE CAN BUS AND EXPECT IT TO WORK!!! Additionally, any of the devices on the CAN BUS must be no longer than 500mm from the BUS itself and the BUS can be no longer than 16m total. In my experience, the CAN BUS is quite tolerant to deviations from the specifications, however, when I work with the CAN BUS I adhere to the specification and do not have issues whereas I have seen issues when things are haphazzardly attached.

Normally on the 08, I would connect the SLM directly to the 79pin ADL/2 connector in the unused CAN slot and power it from the ADL/2 power and ground pins.

After you verify your wiring, I would fthen start by reviewing the configuration. There is no CAN setup or template required, that is handled internally by the software. You need to check the Functions - Shift Lights and Functions - Shift Light Module. I would ensure the proper channel names are used to do the comparisons and then I would go to Online - Monitor Channels and Online - Simulate to test the functions. It may be possible that the new ECU has different channel names.

 

@amso3 : I have my VBOX Lite connected to this one. I am going to try to disconnect it, just to see... good idea

@Geoffrey : I understand the design : 2 twisted wires with a resistor at each end, but I have read somewhere that one could had a resistor if connecting to far from the bus. Also, I have found on the Motec forum someone that did just like me in the first place : Connecting without resistor, and some Motec tech told him he was lucky it ever worked and to add one. He did it with success. I just tried to replicate that.

What questions me, is that the original alarm and shift light lamps on the dash still work perfectly when a condition is matched. There were working in parallel with the SLM before.

We have checked the wires and all seems fine. I am gonna recheck the config

 

...and all information on The Internet is true...

 

Not what I said. Just thought that Motec techs know their stuff...

Config seems fine. More cabling investigations to come... :-\

Thanks for your help ;-)

 

The advice you read on the forum was for an installation where NO terminating resistors were installed and normally it will not even work. Installing at least 1 terminating resistor would likely allow the system to work (remember my comment about it being forgiving) but still is not per the specification. You already have a CAN BUS that meets the specification and adding an additional terminating resistor will only create new problems.

Even the "experts" sometimes don't understand the specification. I'll give you an example: When the Bosch M4 ABS unit first came out, the wire harness supplier built a harness that connected to the miniautosport 5 pin connector near the ECU. Remember, this connector is a "branch" off the CAN BUS and therefore cannot exceed 500mm in length and can only have 1 device attached. The ABS wire harness was designed to connect to this connector, run all the way to the front of the car to the M4 ABS unit where there was a terminating resistor (now 3 total installed in the car). The wire harness then ran back to the YAW sensor on the center tunnel near the rear of the car where an internal to the sensor terminating resistor was also (now 4 terminating resistors total). In some cars, the system ran Ok (recall my comment about the BUS being forgiving), but in others, the system malfunctioned along with the ADL dash. I ended up cutting out several of the terminating resistors and redeisging the BUS so it began with the ABS YAW sensor and ended with the MS 3.1 ECU, the two devices where the terminating resistor could not be removed. The systems worked correctly once the CAN BUS was properly designed.

Remember that BOSCH would only allow a single vendor to design and build the wire harnesses per application due to the liability and potential risk from a malfunctioning brake system...They did finally redesign the harness after I provided proper drawings.

 

Update : You were right, a cabling issue. My mechanic seems to have confused the wire colors...

I have removed the (stupidly) added resistor, redone the cabling and now everything is fine. Fixed yesterday...

Many thanks Amso & Geoffrey for your very interesting explanations ! Another challenge for you in my ABS thread ;-)

 

Great! Which wires were swapped? Just in case I run into the problem on another car.

 

Can't get hold of Geoffrey any one know if he is away ?

 

An incredible thing that prove (if need's be) that the gremlins do exist !

Him and I can not believe he has done it.

-12V swapped with +12V
+12v swapped with can low

Only one wire correctly connected. Unbelievable.

The most important things are :
* Geoffrey is right (who said "as usual" ? ) : No resistor to add on a standard cup CAN bus
* Diagnosis should always be :
1. Blame it on the mechanic
2. Blame it on Porsche
3. Blame it on Motec
4. Blame it on Bosch
5. At last, check the damn wiring calmly after the end of the season
* The SLM is robust enough to be wiring abused without exploding (haven't tried to put +12V on the CAN... yet ! )

 

Wow! That's scary....