Technical Aftermarket Cruise control, CAN-B hi & lo strange voltages

[ToreV]

Hi,

Unusual voltage on CAN hi/lo, both direct and on OBD port.

Ive got a "precision cruise control" kit for my 2008 2.2 X250. Came with kit and instructions specific to my car.

All works except for CAN connection. And I'm getting weird voltage readings. I was getting 5v and 0.7v respectively, and thought surely i must have the wrong cables. But according to the training manual specific for the 2.2, im using the exact correct points.

To verify i measured pin 6 and pin 14 on the OBD plug, and by golly i see the same. 5v and 0.7v. This cannot be correct? I see the same if i disconnect the cruice control or not.

This is the instructions i got, and it matches the Training manual.

What is most shocking to me is the pins on the OBD??

But at the same time i can connect using the OBD using AlfaOBD or MultiECUscan just fine.

What the heck is going on? My multimeter is hardwired to negative battery when measuring.

I would expect to read between 2 and 3 volts on both.

Do I have a broker CAN? I would expect more issues right?

 

[ToreV]

Ive just checked the resistance over the CAN, and im getting 120ohm between pin 6 and 14 on the obd port. Doesn't this indicate i have a broken connection somewhere?

But its weird as everything else works, as does the OBD port.

 

[Anthony489]

Hi Torev

The Ducato uses a C-CAN bus network for Vehicle Dynamic Components, and a lower speed B-CAN bus network for Bodywork functions. It is the low-speed bus which is accessible at the OBD socket on Pins 6 and 14. The low-speed bus wires are black/pink and white/pink.

I suspect that Fiat used the ISO 11898-3 low-speed (fault-tolerant) standard, which has larger voltage swings than "normal" CAN (see picture). However, it's always possible that Fiat dreamed up their own standard. If you measure between the bus lines you should see four termination resistances (two lines, two ends) in series/parallel, which will be the same as one termination resistance. So 120 ohms sounds OK.

 

[ToreV]

Hi Torev

The Ducato uses a C-CAN bus network for Vehicle Dynamic Components, and a lower speed B-CAN bus network for Bodywork functions. It is the low-speed bus which is accessible at the OBD socket on Pins 6 and 14. The low-speed bus wires are black/pink and white/pink.

I suspect that Fiat used the ISO 11898-3 low-speed (fault-tolerant) standard, which has larger voltage swings than "normal" CAN (see picture). However, it's always possible that Fiat dreamed up their own standard. If you measure between the bus lines you should see four termination resistances (two lines, two ends) in series/parallel, which will be the same as one termination resistance. So 120 ohms sounds OK.

Thanks, ok that clarifies some stuff. Can I ask you where you found that graph? Would be nice to send that back to the company i bought the cruice ctrl from.

They claim at least my voltages are not correct.

 

[Anthony489]

Hi

See: http://www1.gcanbox.com/fsd/gsxw/high-speed-CAN,low-speed-CAN.html

 

[Kezzza]

Hi,

Unusual voltage on CAN hi/lo, both direct and on OBD port.

Ive got a "precision cruise control" kit for my 2008 2.2 X250. Came with kit and instructions specific to my car.

All works except for CAN connection. And I'm getting weird voltage readings. I was getting 5v and 0.7v respectively, and thought surely i must have the wrong cables. But according to the training manual specific for the 2.2, im using the exact correct points.

To verify i measured pin 6 and pin 14 on the OBD plug, and by golly i see the same. 5v and 0.7v. This cannot be correct? I see the same if i disconnect the cruice control or not.

This is the instructions i got, and it matches the Training manual.

What is most shocking to me is the pins on the OBD??

But at the same time i can connect using the OBD using AlfaOBD or MultiECUscan just fine.

What the heck is going on? My multimeter is hardwired to negative battery when measuring.

I would expect to read between 2 and 3 volts on both.

Do I have a broker CAN? I would expect more issues right?


View attachment 392489

That’s where I connected mine to. Worked great for a while the started getting faults thr obd. Engine management light came on, throttle pleased itself revving full blast. Had to pull over a few times switch off then it was ok until the next time. The throttle plug might have come loose. Haven’t sussed it yet, too cold.

 

[ToreV]

That’s where I connected mine to. Worked great for a while the started getting faults thr obd. Engine management light came on, throttle pleased itself revving full blast. Had to pull over a few times switch off then it was ok until the next time. The throttle plug might have come loose. Haven’t sussed it yet, too cold.

Ohh wow, that sounds like a bit of a nightmare. If you can, please update if you can.

 

[Kezzza]

I’ve not reconnected yet. I will try to remember to send update. Merry Christmas .