Cruise & Speed Limiter Fault C5 X7

[admiral51]

Ady i have re read the Devil Car thread and i would look at replacing the Air Doser. Apart from gut instinct i cannot confirm why, but from memory of having that particular car for whatever reason they are linked. How it affects the code P0299 i do not know but once both the solenoid valve and the air doser were changed ( along with the actuator but that was delivering boost as detailed prior to change ) the cruise/limit control were solved.
It may be that whatever ECU's take full control of engine management when engaged produce a default code of P0299.
I think the one way valve maybe the Air Doser.

Colin

[ADY-ULTRAS]

I changed the solenoid turbo valve, I checked the turbo actuator and clean the MAF sensor.
Now, when I set the cruise control, when it needs to force it (like going from 45MPH to 70MPH on uphill) it's coming off and it's not working anymore. I need to stop the engine for a couple of minutes in order to be able to activate again the cruise control.
On diagnose it gives now errors from the electric power steering - absence of communication with ECU, (U1108, U1208, U1308) - intermittent. From the driving point, I can't feel any difference and if I accelerate it from pedal and then set the cruise control it's working fine.
Did anyone had any issues like this? It's starting to get me mad... Thanks!

[ADY-ULTRAS]

Now it's getting really weird. On my way home, the cruise control came off but on diagnose were no fault codes. Today, cruise control came off again. So, if I reach the set speed and then activate cruise control works fine. If I use the cruise control to get to the previous set speed, it's coming off. Any ideas?!?

[GiveMeABreak]

That will be because when you set the speed that you are already travelling at, the engine has already reached the desired speed, so setting the cruise is fine.

However when you are at say a much lower speed and then try to resume the previously set much higher speed, this is much the same as flooring the vehicle to reach the memorised speed as quickly as possible.

That being the case, if there are any issues with the engine management or components, the engine management ECU will prohibit and deactivate the speed control functions as a safety feature. So, you need to do some investigation. This would make sense given the codes you have supplied, as:

U1108: No communication with the engine management ECU fault: No signal
U1208: No communication with the engine management ECU fault: Data invalid:>

Possibility 1
-The time for recording the fault code is 500 milliseconds
- The clutch pedal sensor values sent by the engine management ECU are not coherent with those of the ESP ECU
Possibility 2
- The time for recording the fault code is 500 milliseconds
- The datastreams from the engine management ECU are not valid
Possibility 3
- The time for recording the fault code is 500 milliseconds
- The accelerator pedal sensor values sent by the engine management ECU are not valid

U1308: No communication with the engine management ECU fault: No signal:>

Possibility 1
- The time for recording the fault code is 500 milliseconds
- Data from the engine management ECU absent
Possibility 2
- The time for recording the fault code is 500 milliseconds
- Incoherent data coming from the engine management ECU

These can all be to do with a failed download of the engine ECU, fault on the CAN network , Electrical Connections, ESP ECU - Have you undertaken any work on the wheel speed sensors / brake discs / pads lately?

[ADY-ULTRAS]

No underworks on the wheels /pads / sensors. Those 3 error codes where shown only once and after deleted never appeared back but now the are no codes but still the cruise control goes off when it needs to reach the speed and is working fine after I stop the engine and leave it for a couple of minutes. I can't feel any difference when I accelerate it, with the cruise control working or not. Also, if I press the pedal all the way down the car goes very well with no issues. As there are no fault codes now, I don't know what else to do... It's really annoying!

[GiveMeABreak]

Ok the problems you may have are with intermittent faults. These will appear when the conditions trigger and can disappear after the engine is switched off and restarted or when conditions that caused the faults return to normal.

There should be a record stored on Diagbox of the triggered fault codes so you will need to access the log to see them

[ADY-ULTRAS]

I'm using Launch and it doesn't show any codes. Do you reckon that Lexia might find more fault codes?

[GiveMeABreak]

Diagbox is the dealer level software. If you get it, stick to V7.62 for your C5 X7.

[ADY-ULTRAS]

Thanks mate, I'll see what I can do and let you know!

[ADY-ULTRAS]

Quick update! I found on a French forum that all that 3 codes are made by a faulty alternator pulley. I checked mine and was faulty but I couldn't take it off so I changed the whole alternator.
All went well for 2 days, the car was pulling with 4 person without no problem from 50 to 75... on the third day, alone in the car, when I tried to get to 70 from 55, the cruise control came off. I've done a scan and no faults found, not even on history. After restarting, the cruise control works fine. Now I don't know what to do anymore... any ideas?

[ADY-ULTRAS]

Update! I manage to find out the error.
After my cruise control went off, I did a scan and found P0299 - Turbo pressure electrovalve control. Flow too low.
After a couple of minutes left with engine off, the error disappear and the cruise control is back on. Interesting fact is that the error is gone from history as well, that's why I didn't find anything when I was performing a scan.
Now, the electrovalve was changed and its new but still get the cruise control off when the car is accelerating by it self. There is no change on how the engine works, apart the cruise control.
Any ideas? Thanks!

[GiveMeABreak]

Whenever fault P0299 is present the cruise control gets deactivated. It's the engine management ECU that does this for safety reasons when there is an issue.

Here's the fault descriptor for the P0299 fault that may give you some pointers:

Fault Code:
Description of Fault:	Turbocharger pressure signal: Pressure too low in relation to the reference value. Difference negative for 5 seconds, between the turbo pressure reference and the measured turbo pressure: The pressure measured is lower than the reference, around 300 mbars for an engine speed above 2500 rpm. The fault can be active: In particle filter regeneration with engine speed above 1800 rpm Not in particle filter regeneration with engine speed under 1500 rpm
Conditions for Fault to clear:	Driving for 5 min with several full load accelerations for 10 seconds
Downgrade Modes whilst Fault is active:	Use of the flow calculated Cutting of the EGR butterfly (turbo air cooler), EGR valve and bypass butterfly (inlet air heater) in all operating modes Cutting of cruise control Change to "easy move" torque invalid (Deactivation of automatic mode for the electronic parking brake)
Symptoms:	Lack of power Noise Smoke from the exhaust
Suspect Areas:	Air meter restricted Clogged air filter Obstacle obstructing the air passage Air lock between compressor and engine Turbocharging pressure sensor Turbocharger position copy sensor Vacuum problem Variable geometry of the turbocharger jammed in the "minimum turbo" position Faulty turbocharger

[ADY-ULTRAS]

The cruise control is coming off only when I set it at low speed and the ECU is accelerating in order to reach to the desired speed. If I set it when I'm at the desired speed, it's working fine. After is coming off, there is no error on the dashboard, no symptoms, the acceleration works fine, only the cruise control / speed limiter doesn't work. After I stop and let it reset it, there are no errors on history and the cruise control / speed limiter are working fine. Just don't know what to do more....

[GiveMeABreak]

Ok, to explain:

1) You may not get a message on the dash or any other dash messages or warnings - but if the relevant fault code is triggered, the engine ECU will still go ahead and inhibit the cruise and speed limiter functions.

2) If the fault is classed as a temporary fault, then as soon as the conditions permit and the fault becomes inactive (as in the case of stitching the ignition off for example), the fault can be reset and therefore the speed functions like cruise will work again - only until the fault is triggered again.

So if you think about it, when you are accelerating manually, the cruise is not active. When you then reach the desired speed and then set the current speed, the cruise is only holding the speed. I suspect if you use the cruise buttons the set speed to accelerate, then the same will happen sooner or later and it will disengage again.

It's a safety operation - as I mentioned - any time the engine ECU detects a fault somewhere that concerns the engine speed / fuelling / air / or other issues, it deactivates the speed assistant features.

These features rely on all the sensor information, vehicle speed and engine system parameters being within tolerances - anything out of these parameters can trigger the deactivation of certain features, as given the nature of cruise control operation for example - this could have serious implications if there was a malfunction - to they are more sensitive to everything being spot on.