Hello, 

 

My wife’s S Max has cut out twice on two completely separate journeys, while driving on motorways around 50/60/70mph. 
 

The engine completely cuts out and then only starts again after a round 3/4 mins. No EML light before or after.  And then it drives absolutely fine.

These are the codes that have been read:

P02FA-99 | Diesel Intake Airflow Position Sensor Minimum / Maximum Stop Performance

P0170-00 | Fuel Trim (Bank 1)

P0251-21 Injection Pump Fuel Metering Control A

Please any help is required, we are expecting twins any day now and moving house in a week! 

Thank you x

 

Although I still don't understand why a diesel needs a throttle body, the first code implies that and this thread SEEMS to confirm (Google each code and try to make a summary which covers the fault but don't fit new parts unless it's definite?):

https://www.kugaownersclub.co.uk/threads/p02fa-diesel-intake-air-flow-position-sensor-min-max-stop-performance.18637/
The other things are checking for any wiring damage and continuity (or find someone who can and diagnose it) before changing anything.
Sorry I can't wave a Magic Wand but this post should keep it at the top of the threads

6 minutes ago, Shearers said:

Although I still don't understand why a diesel needs a throttle body,

A diesel engine still needs a controlled flow of air as well as injected fuel.

27 minutes ago, Shearers said:

Although I still don't understand why a diesel needs a throttle body

It does a few things.

It chokes the Airflow at switch off to stop the Engine running on, it controls the amount of EGR flow at times by increasing it a lot when lifting off the Accelerator and is used during Regeneration to increase the Temperature in the DPF.

Some cars also have two of them to increase or decrease the flow through the Intercooler.

Diesels only got throttle bodies from around the turn of the century.  It is purely for comfort and emissions regulation.  Diesels always take a full air charge as standard and are only controlled by the fuelling, they do not need an air based throttle.

Unfortunately all that extra air contains excess Oxygen, which combines with Nitrogen at high temps to create NOx in diesels during idle or cruise conditions.  The best way to reduce that is simply to reduce the amount of Oxygen in the cylinder, just enough to burn the diesel, no more.  That is done using EGR.  Exhaust gas is mostly Nitrogen which is inert on it's own, and that physically blocks extra air (including oxygen) getting in from outside.  However, fluid dynamics shows that opening an EGR valve doesn't necessarily mean the engine will take as much of that gas as we need it to.  So throttling the intake using a 'petrol' throttle valve makes sure that the engine cannot pull enough air from outside and therefore must pull all of the gas from the EGR valve instead.

The comfort comes from it's anti-shudder function as above.  One single 'stop' at switch off, instead of the clattery noise that old diesels made when switching off.

And finally DPF regen is reliant on enough excess Oxygen within the DPF to light the soot and keep it burning.  However, we still don't want so much oxygen in there that the temps runaway and crack the DPF core or cause an engine bay fire, so the throttle body can be used to control the level of Oxygen in there as well.

Thanks for the techie bits...

@Tc9117 hasn't been back yet but it does look like codes should be cleared and see what stick?

There's throttle body info:

https://www.obd-codes.com/p02fa

MAF Sensor:

https://www.obd-codes.com/p0170

Fuel metering:

https://www.obd-codes.com/p0251

So, plenty to check, including air flow on live data to see if it is plausible and increases with revs plus inspection and testing of MAF plus inspection of wiring on all components mentioned above (I think there is a solenoid controlled by PCM  signals which manages the HP pump?) 

Then inspection and testing of throttle body (wiring/signal/voltages first) 

L-R engines seem to have a lot of issues with spindle sticking?

As usual, that would be my version of an inspection along with any relevant live data/sensor outputs on Forscan first?

And, of course for any fuel related problem, my strategy is to change the filter as the easiest/cheapest most critical approach?

Anyone?

 

46 minutes ago, Shearers said:

it does look like codes should be cleared and see what stick?

Yes, some of the Fault Codes may be historic. The codes should be read with something like FORScan that can read manufacturer specific codes as well as generic ones, these Codes are all generic.

The Throttle Valve Min and Max position is easily checked by looking at Live Data, especially at switch off. The Valve closes for a few seconds to kill the Engine then quickly cycles fully on/off a few times to shake off any crud. The Min and Max positions usually need to be Learned and FORScan will probably have a Service Procedure to do that.

If it is not showing as opening and closing fully then it can be easily checked physically by looking at it with the pipework removed.

The MAF is easily checked on a Diesel Engine by comparing it with the MAP, if graphed they should be the same as each other, with different values obviously. I doubt if the MAF is the problem.

I think there is a Fuel problem that may be mechanical but probably electrical related. These faults are difficult to diagnose.

8 minutes ago, Tizer said:

I think there is a Fuel problem that may be mechanical but probably electrical related. These faults are difficult to diagnose.

Thanks...Well, that's plenty above for @Tc9117 to go on?...