Technical Lost connection with the Cruise Control module

[Dlub]

Hello guys I need some advice for my cruise control issues.

I’ve got a Fiat Grande Punto 1.4, 8v from 2007 born with cruise control.

This happens 2/3 times I try to use CC:
Cruise control turns on with the display text and dashboard light, but it doesn’t engage. When turning it off on the stalk the dashboard light doesn’t turn off and the car needs to be turned off for a while before the dashboard light turns off.
This error can be triggered stationary and while moving in the highway, however it has never occurred with the engine turned off.

MES gives me the error code: U0405-81 “lost communication with cruise control module”.

• this error code was hard to find, it isn’t always logged.

In the description it tells me it’s a communication fault on the CAN bus.

Everything else works and I have no other error codes so the CAN bus connections should be ok? I’ve checked the earth connections and they are fine. A new battery was fitted 2 years ago. MES reports no problem with clutch switch and brake switch and can see when they are pressed. MES reports no need for proxy alignment and CC turned on.

• Funny thing, when the error occurs MES can see the CC be turned on and off however the dashboard light stays on.

Is the next move a new stalk? I assume the “cruise control module” is the stalk?

Any suggestions? I really want to use the cruise control again.

 

[GrandePunto PL]

If possible (if it's not too invasive), you can try to dismantle the stalk and clean internals, contacts.
This could be similar effect to the blinking lights (due to dirty contacts in the switch).

Or some other parts force the "control module" to switch it off (like gas/accelerator pedal potentiometers), driving conditions.
Cruise control is managed by Body Computer, so there's no separate "control module" (maybe there is some electronics in the stalk, but calling it a "module" is exaggeration).

PS
Read this (whole thing): https://4cardata.info/elearn/199/2/199000000/199000001/199000003/199000621

 

[Dlub]

So i've been reading through your link and some of Bearnie's old post and to my understanding the cruise control handle is actually just a bunch of resistors the BCM are reading.
It's been a few weeks since last time i was able to engage the cruise control. I'm also seeing it turn on when starting the car sometimes even though it's turned off on the stalk? And when turning it on i've have not been able to turn it off. I'm thinking that a contact issue that leads to a higher resistance would trick the BCM to think CC is turned on, and when switching it on, on the stalk it will give a very wrong resistance reading for the BCM resulting in either the BCM disabling CC or a nonsense signal to the ECM thus the invalid serial data error code from the ECM.
I'm using the car every day so not keen on removing the steering wheel to measure the resistance on connection 10 and 8 for the CC and it has been discussed wether E-learn reported resistances are correct or not.

 

[AndyRKett]

I’d probably remove the the unit from the steering column and try to clean up the contacts, if that is not working then maybe look around for a replacement, the issue is the unit is all one piece for the CC as well as the indicators and light stalks so I you need to replace the whole thing, fixing it is probably well outside the realm of any DIYer

 

[Dlub]

The cruise control worked yesterday to my surprise, it has been a few weeks, however it stopped working when I needed it on my way back from work.
So I measured my stalk’s resistance today and the stalk is working perfectly fine:
On: 2480
Res: 120
UP(+) 340
Down(-): 730
I’m starting to fear it’s the BMC or ECM. What is my next move. Any suggestions?

 

[Dlub]

So I also sprayed the connectors on the ECM, BCM connnector D and the the stalk unit with contact cleaner. I took the car for a test drive and of course it worked. I will be really upset if this was the fix. Goddammit FIAT and its connections; the brake lights, the heating fan resistor, oil pressure sensor, starter unit earthing, steering angle sensor in the electronic power unit. Every contact seems to oxidise combined with a very resistance sensitive computer. Rant over..
I will see if the problem reappears next week. It’s an old car and it is probably a miracle it still drives around after seventeen years.