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Discussion Starter #1
Driving on A303 last evening, bit of rain so not too good, doing 65 ish and came up to a slower truck on a slight incline. Dual carriageway, so pulled out to overtake and put my foot down a bit to accellerate.
Beep! Engine fault. And limp mode kicked in immediately. Stuck in outside lane, car coming up behind and no accelleration. Wonderful.
Limp mode continued, but found a layby and stopped. Turned ignition off then on again. EML still lit and warning comes up, but driving off, normal performance.

So today checked with generic ELM EOBD anf it tells me P2448 Secondary Air Injection bank 1 - Air flow high. No other faults found, none in memory.

Eventually booted up the laptop and ran Diagbox (what a slow business).
That then came up with several ECU codes.
P2448 Inlet air circuit, air flow greater than maximum.
P02EC00 Inlet Air circuit - air flow lower .
P2A00 NOX sensor - richness measurement faulty. Temporary.
P2463 Particulate filter detected overloaded. Temporary. Checked this in more detail and the regen seems fine, and current figures suggest there was no permanent problem. But I do regularly get the "risk of clogging" warning which stays on for a minute or so, sometimes 3 or 4.

So does anyone know what this P2448 is all about, and why on earth it triggers the limp mode when if you turn the ignition off and on the limp mode goes away.

This is the 2015 308 SW 1.6 Blue HDi 120.

What inlet air circuit is it talking about? I wan't aware diesels had secondary air injection, and anyway it's normally only used at start up, not on an engine that's already 50 miles into a journey.
 

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Those first two codes on a HDI are normally down to mismatch in boost level and air flow seen/expected, it can be caused by a faulty MAF, Vacuum leak, Sticking EGR or Turbo Vanes or a boost leak.
 

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Discussion Starter #3
Car has done 44k miles. It would be nice to think the turbo lasted longer than that.
Looked at live data and everything matched at that time. But of course the fault wasn't appearing then.
A boost leak would be a leak in the air inlet after the turbo I presume. That would cause the second code no doubt, but it was marked as temporary. Nothing obvious as far as I can see.

One problem is my Diagbox V7.83 doesn't recognise the engine ECU so I have to select what seems to give some results. I might have got that wrong.

There was also another code referring to a fault in the DMF, but also a note to say this could be a false report depending on software version.

Still don't understand why it triggers the limp mode though, a dangerous situation.
 

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Discussion Starter #4
I also sprayed a can of EGR cleaner through the system a couple of weeks ago, so hopefully the EGR valve is not sticking. It also went through the turbo so might have cleaned that up a bit too.
Car didn't get used much in lockdown, and did too many short journeys I think. I normally do a several long journeys each month. Best part of 1000 miles in the last 2 weeks.
 

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Discussion Starter #5
Happened again, this time at low speed. Again limp mode kicks in. Doing under 30, accellerated away from a roundabout and beep.
So, checked freeze frame, first on my generic OBD app. P2448
Load value 98.8%
Engine temp. 84 degrees.
Speed 26mph.
RPM 1360
MAF 41.3 gm/second.
Fuel rail pressure 88350KPa.

But checking with Diagbox it does say readings may not be accurate - Diagbox doesn't automatically select the ECU P2448 Air flow greater than maximum.
Date 50895052 - what does this mean?
Accellerator pedal 49%
Speed 24 kph ????
Engine temp 21 degrees ???? I know it was up to temperature.
RPM 2514 - I'm certain it wasn't that high.
Turbo pressure 1.79 Bar.
Air intake temp 13 degrees.
Measured air flow 901 mg/stroke
Ref air pressure 867 mg/stroke.
EGR value 4%

But does this suggest the inlet air flow was too high?

Diagbox P02EC Air flow lower that theoretical.
Date 50901120 ??
RPM 1161
Accell pedal 0%
Speed 51 kph
Engine temp 57 degrees
Turbo pressure 1.07 Bar
Air intake temp 16 degrees
Measured air flow 503 mg/stroke
ref air flow 427 mg/stroke.
EGR position 0%.

Can anyone make any sense out of these readings please?
 

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Discussion Starter #6
So do these figures make any sense to anyone?
 

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It looks like a overboost is being detected so either a issue with turbo actuator sticking on, solenoid valve or MAF maybe faulty and over reading.

In live data what is boost actual and requested readings

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Discussion Starter #8
Well, boost pressure at time of fault was 1.79 Bar according to the freeze frame data. Trouble is, I'm not certain I'm getting the correct information as Diagbox isn't automatically recognising the ECU. I've selected the only one in the list provided that gives any result, but still not convinced it's correct.

I also obviously need to check under the same circumstances as when the fault happened. Not so easy to replicate, but I will try again.
 

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The core data should be fine as it is OBD standard data. Other data such as the date can be any format so may change version to version.

Does freeze frame give expected boost as well or just acctual

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Discussion Starter #10
Only actual. Live data gives both but that means catching it at the right moment.
Seems to happen on a slight uphill gradient with more than just light accelleration.

Maybe I should try a few test runs, I did manage to cause the fault on a private road some time back (was the A3 many moons ago).
 

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Not sure if your engine variant has swirl flaps on the intake.

On my old 807 I had random overboost and air flow issues which only occurred when I accelerated after cruising for a while

It turned out to be a faulty swirl valve actuator which was slightly leaking vacuum when open.

When cruising the valve would open and vacuum drop slightly affecting turbo actuator, this would cause ecu to open actuator more to maintain same boost

When I would then try and accelerate ecu would shut swirl flaps the vacuum leak would stop and the sudden increase in vacuum would cause the turbo actuator to move and overboost the engine before ecu could react.

It was a real random and intermittent fault and took me ages to find. I finally found it by going over every item on the vacuum system with a vac gauge looking for a leak.

Once found I blocked off the hose to the actuator and drove the car for a couple of weeks to confirm I had fixed it before changing actuator.

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Discussion Starter #12
Well I had to look up swirl flaps.
Not sure. I did have to remove part of the inlet tubing from the intercooler to get access to a fuel pipe. I then noticed what looked like a butterfly valve beyond it, would that would be the swirl flap? But most references suggest there would be two channels into the intake manifold, just one channel would apply to Tumble flaps as in this description. The function of tumble flaps and swirl flaps
But your suggestion would apply in both cases.
Which way would the valve be positioned in the "off" position, as when I saw it it looked like a closed butterfly.
 

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I think that maybe the doser. I will have a look to see if they list an actuator for 120 bluehdi.

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Free info is a bit sparse on the blue HDI, looking at some other models I cannot see a swirl flap actuator.
 
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