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Technical Cruise Control Disconnection

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Technical Cruise Control Disconnection

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DD53

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I have a problem with my 500x cruise control. When I press the RESume button to restore the previous set speed, after a while the cruise control disconnects itself as if the clutch or brake pedals were pressed.
It happens only with the 6th gear so, in my opinion, neither the clutch and brake switch should be involved nor the speed control switches on the steering wheel .
It seems to me that the problem came out after the ECU software update was installed in January last year, nevertheless Fiat service people say there’s no relation between the ECU and the cruise disconnection.
They checked the ECU registry and found no errors, everything is right.
Does anyone have suggestions ?

Thanks
Daniele
 
I had similar issue way back and it turned out to be a small sensor which had failed something to do with the clutch travel even if neither brake or clutch had been touched. Fixed under warranty eventually, 3 attempts and 2 weeks in dealership, as it was intermittent and left no warnings.

Stu
 
Thanks a lot Stu, I will check again even it is a little bit weird it happens on with the 6th gear only and never in 4th or 5th.
My case is not intermittent, it occurs every time I press the RES button to restore the speed. Once the speed has been restored the cruise works perfectly.

Daniele
 
I'm wondering if the Cruise Control is disconnecting because in 6th gear, due to incline, wind resistance, other retardation, 100% throttle is being request and the engine ECU is saying that at this RPM in this gear and this throttle value I *really* need to drop a gear so disengages Cruise Control so the drive can take the appropriate action.

The latest software update you had may have had this function added but as a "function" as opposed to a "fault fix" it may not be listed/disclosed to the dealer.
 
I think thats intelligent analysis, and even if it isn't the correct answer makes perfect sense to me.

s130 said:
I'm wondering if the Cruise Control is disconnecting because in 6th gear, due to incline, wind resistance, other retardation, 100% throttle is being request and the engine ECU is saying that at this RPM in this gear and this throttle value I *really* need to drop a gear so disengages Cruise Control so the drive can take the appropriate action.

The latest software update you had may have had this function added but as a "function" as opposed to a "fault fix" it may not be listed/disclosed to the dealer.
Click to expand...
 
Thanks a lot guys.
I think the analysis could be correct and so I have a few chance to fix the problem.
Actually the event comes out almost immediately when the highway is climbing.
It shouldn't happen at 130 - 140 Km/h and 2500 RPM being that car a diesel fuel one, 120 CV.
 
Interesting comments.

My AT9 is the 2.0l, vs the 1.6mjd it has approx 15% more power, 10% more torque, but weighs 13% more. So very much the same power/ torque to weight ratio.

When I set my cruise over say 65mph/ 100km/h it's in 9th and always stays there even on large inclines. I can't remember it changing down to 8th.

Furthermore the gearing's longer. On the speedo at 2,000 revs it shows 75mph/ 120 km/h, so say at 2,500rpm it'd be showing somewhere around 150 km/h.

Bearing all this in mind I do wonder if my initial thought of the car's pulling in a gear too high and disconnects due to that is the answer. I'm on the fence.

What I would try is taking it on the route/ stretch where it disconnects in 6th and set the same speed, but next time try the same but in 5th instead and see if it disconnects.
 
It happens in auto mode, I never use the cruise control while in sport mode, it doesn't make sense in my opinion.

I confirm that the problem happens only with 6th gear.
No problem on the same road at same speed with 5th gear or same rpm.

By Daniele
 
Sounds like the sensor thinks the engine is labouring in 6th and disconnects it, perhaps prematurely.
 
Problem fixed. As soon as I've replaced the clutch everything is working fine again.
Probably the cruise sensor detected the imperceptible slippage the clutch had at the beginning of its failure.
 
Interesting to know.

In our modern cars the computers dictate what does and does not happen. Like all computers/systems ALL fault/action possibilities are not publicised.

So in your case a detected possible clutch slip would I think trigger the Cruise Control to stop applying engine power that would just burn the clutch out.

All makes sense from an engineering point of view but from a user point of view there are issues.

1) The engine management system can probably detect clutch slip during non stressful driving long before the driver does

2) No end user documentation about ALL the conditions that could cause Cruise Control Disconnection

The stupid and I would say irresponsible thing is that if the system can detect a clutch slip (enough to disengage cruise control) then why is that communicated to the driver?

Actually this is nothing new. It is manufacturers hiding behind codes. Get a fault code and the EML comes on. User handbook says "report to dealer". This leaves the customer worrying what damage etc. may be done if they don't do this in the next MINUTE.

Examples of the stupidity:

An EML/fault for cam belt timing/cam shaft timing errors should be yes and error code but also driver information such as: 1-Critial Stop Engine Now -Seek Recovery or say 2-Proceed with caution, low revs, ..., report to dealer ASAP.

My software would do this. The best next step I guess manufacturers will come up with is:

a) You're lucky today
b) You're shafted
 
s130 said:
Interesting to know.

In our modern cars the computers dictate what does and does not happen. Like all computers/systems ALL fault/action possibilities are not publicised.

So in your case a detected possible clutch slip would I think trigger the Cruise Control to stop applying engine power that would just burn the clutch out.

All makes sense from an engineering point of view but from a user point of view there are issues.

1) The engine management system can probably detect clutch slip during non stressful driving long before the driver does

2) No end user documentation about ALL the conditions that could cause Cruise Control Disconnection

The stupid and I would say irresponsible thing is that if the system can detect a clutch slip (enough to disengage cruise control) then why is that communicated to the driver?

Actually this is nothing new. It is manufacturers hiding behind codes. Get a fault code and the EML comes on. User handbook says "report to dealer". This leaves the customer worrying what damage etc. may be done if they don't do this in the next MINUTE.

Examples of the stupidity:

An EML/fault for cam belt timing/cam shaft timing errors should be yes and error code but also driver information such as: 1-Critial Stop Engine Now -Seek Recovery or say 2-Proceed with caution, low revs, ..., report to dealer ASAP.

My software would do this. The best next step I guess manufacturers will come up with is:

a) You're lucky today
b) You're shafted
Click to expand...
By the time the ECU would detect a timing belt fault is imagine it would be too late already

Belts tend to just go from work it 100% fine to snapped is second's
 
chris3234 said:
By the time the ECU would detect a timing belt fault is imagine it would be too late already

Belts tend to just go from work it 100% fine to snapped is second's
Click to expand...

Sadly not true. On the Coupe 20V we had the double sided serpentine auxiliary belt started fail. This led the one of the end chords coming loose like a carpet end thread and bot ingesting down behind the crank pulley wheel wrapping itself around the crank cam belt drive sprocket. This caused the cam belt to start to lose timing. The EML came on which my wife, who was driving alone, spotted the EML and stopped the car.

This I gather has happened to others (not only on the Coupe) where either the aux belt or other debris has found its way into the timing belt area.

No way is it safe to drive to the dealer as instructed in the User Manual :eek:
 
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