Unusual Diagbox result

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jml
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Unusual Diagbox result

Post by jml »

I live in a hilly area and, in particular, I frequently climb a straight a quarter mile uphill slog which used to annihilate my fuel consumption- 9.4 mpg on instant trip all the way up the hill. Some years ago I found out that if I accelerated heavily on the downhill stretch before the uphill sectio I could climb the long uphill bit just tickling the throttle with much better fuel consumption. This worked successfully for many years.

Recently however as I hit the bottom and start to climb the hill the antipollution warning light comes on and the car goes into limp home mode. It is only in these circumstances that I have experienced this problem.

Checking the car on Diagbox, shows up the two faults as per screenshots below. However if I try to delete the faults it comes up with a warning something like ‘fault not cleared’.

I also have a smaller diagnostic reader that shows the same error codes but, oddly, this one does allow me to delete the fault codes. Checking afterwards with the Diagbox shows that the faults have been deleted.

The car then runs perfectly until I execute my downhill-uphill trick again, although it doesn’t happen every time. I should add that checking the DPF on Diagbox shows everything good (Eolys level ok and filter unclogged with not much deposits)

So,

1) does anybody have any idea why this manoeuvre would cause the ‘anti pollution system faulty’ warning ?

2) What do those fault codes suggest

3) Why does why cheapo tester clear the faults when Diagbox doesn’t ?

Any suggestions would be gratefully received

Cheers

Julian
551E03CB-EF2C-493B-AA03-FA0BC5B6A39E.jpeg
EF68C0E5-A478-481A-956C-17DA5178E451.jpeg
DADC3AA1-29A3-4D6C-A2E4-0FB68212C39E.jpeg

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GiveMeABreak
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Re: Unusual Diagbox result

Post by GiveMeABreak »

Ignore the P1351 error - that's just the glow plugs, but your P0100 relates to the mass air flow sensor.

You'll probably need to test the MAF Julian and get some live data. If there is a break or short in one of the wires further up in the harness it should show up on the graph as you wiggle the harness. If the MAF itself was faulty, I would expect the faults and symptoms to be there permanently, but as it only happens on the upward ascent - it might be enough to disturb a faulty wire...

There are 4 wires on the MAF connector:

Terminal 1: FREQUENCY SIGNAL
Terminal 2: Air temperature signal
Terminal 3: Earth
Terminal 4: 12 volts supply

The frequency signal varies in relation to the air flow.
The frequency of the signal decreases as the air flow increases.
Example:
Frequency = 11000 Hz: Engine stopped, ignition on; (No air flow)
Frequency = 5500 Hz: Engine idling; (Medium air flow)
Frequency = 1000 Hz: Engine full load; (Maximum air flow)

As a Reference Graph, this shows Full load engine speed: You should therefore get something similar with the engine at full load.
C8 MAF Ref.PNG
Key:
"C" Voltage: 5 Volts
"D" Time: 200 ms

The air flow meter consists of two separate sensors:
The inlet air mass sensor (flow meter)
The inlet air temperature sensor

The inlet air mass sensor(flow meter)
From this information the diesel injection ECU determines the following parameters:
  • The calculation of the rate of recirculation of the exhaust gas
  • The calculation of the turbocharging pressure
  • The flow to be injected to limit fumes
The inlet air temperature sensor
The inlet air temperature sensor informs the diesel injection ECU of the inlet air temperature.
From this information the diesel injection ECU determines the following parameters:
  • The calculation of the theoretical volume of air
  • The calculation of the injection advance
  • The calculation of the injection flow
  • The activation of the additional heating (on the order of the BSI1)
Inlet air temperature (°C)Nominal resistance(ohm)Output voltage( volts)
2024002.7
4011001.8
So this might help you with some troubleshooting. As for different diagnostics tools - I wouldn't pay too much attention there really - as if the fault is intermittent it will just come back again regardless. I can't help with the Auto Gearbox fault - but I would get the MAF issue resolved first so you can eliminate that and any 'knock on' faults as a result of this fault.

jml
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Re: Unusual Diagbox result

Post by jml »

Hi Marc,

Many thanks for your speedy and comprehensive reply - as always :)

I will do as you suggest and in fact it is the relative abrupt vehicle motion change - from driving rapidly downhill then suddenly hitting the uphill stretch - so this could well be the thing that sets off the poor connection or loose terminal.

Just to check though, is this the MAF on my twin turbo model (Citroen describe this as the Doseur) ? I replaced it a couple of years ago (with a genuine Pierburg unit) as the plastic gear inside had stripped and I guess I may have strained or damaged the wiring.
5D61F6B2-66B2-4DD7-B69B-1A84B80C22D3.jpeg
C8D2816A-C88A-4E00-862C-1501F72ACF92.jpeg
Cheers

Julian

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Re: Unusual Diagbox result

Post by jgra1 »

hi Julian, I too get different success with different code readers! as Marc I dont worry about it too much but it's handy to have a second opinion/attack angle sometimes :)

that doesnt look like the MAF, the MAF should be engine side of air intake from Air Filter, a plastic black construction with a sensor sitting inside. and a 4 way plug to it, usually its jubileed into the air intake pipework

John

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GiveMeABreak
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Re: Unusual Diagbox result

Post by GiveMeABreak »

No, not the Air Doser Julian - MAF, which is item 29 below :-D :
image_2020-11-26_122303.png
Part 1920HH:
image_2020-11-26_122607.png

jml
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Re: Unusual Diagbox result

Post by jml »

Thanks Marc and John,

That’s easier to access :)

It’s interesting because that doseur also has an air temperature sensor but, of course, by the time the air gets there it’s been heated up by the turbos and then cooled by the inter cooler !

Cheers

Julian