C5 2.2HDI - DPF temp. sensors inaccurate?

[mwj666]

Hi all,

Another query from giving my GFs 2.2 HDI the once over on Lexia yesterday...

Even though the engine had been stopped for about 2 hours, both the upstream *and* downstream temperature sensors for the DPF said 104 degrees, though I'd have expected them to be more or less ambient temperature (about 17 degrees)

On starting the engine, the temperatures rise - but of course I have no idea whether what they are reading is correct or 100 degrees out, and presumably if they are way off beam that will muck up fuelling ratios and also the dreaded DPF regens as even tho' the car *thinks* the DPF is hot enough it won't be

It seems an odd coincidence that if both sensors had failed they would register the same temperature - so does anyone know if the '104 degrees' is the 'baseline' temperature for these sensors ie they are incapable of going below 104 degrees, or are they in need of replacement (AFAIK they are still the 14 year old originals)?

If they are scrap - does anyone know a source for them (other than silly-prices Citroen)? I'm struggling to find aftermarket suppliers, which seems odd as there must be millions of diesel cars out there with these things fitted

Thanks,
Martin

[dnsey]

I have a similar problem on my 2.0 - the downstream sensor has failed.
In my case, it's reading a permanent 308 degrees, which is near enough the default.
Doing a bit of research, I'm coming to the conclusion that there are only a handful of different sensors, with different connectors according to model.
Thinking aloud, I wonder if you could use soap (as when judging metal temperature for hardening etc) to judge the actual temp when hot, and compare that with the sensor reading?
Edit: mine registered a 'depollution fault' as soon as it failed, so yours may well be OK.

[mwj666]

first thing - my mistake, the sensors are of course upstream and downstream of the cat, not the DPF, all thats downstream of the DPF is the pressure sensor pipe.

Looks like the Citroen part numbers (for the 2.2 anyway) are 1628 VZ (upstream) and either 1628RX or 1618 LW (downstream depending on your RP number) - but hanged if I can find any generics that say they will fit

Still none the wiser about whether they are b*ggered or if 104 degrees is the lowest they can measure given thats what they say when the engine is stone cold. Some generic sensors don't go below 200 degrees, some say they go from about -40 upwards

Research continues - and its been throwing out antipollution messages for a while ... rather a lot less so mind you after I took a pressure washer to the damn thing, which I had to do in situ (front end up on ramps, split centre joint, drop back of DPF to put it on a slope and remove the front EGTS to provide a drain the otehr side of the DPF) as I'm damned if I can shift the nuts attaching the DPF to the cat and they are welded into the cat and didn't want to risk shearing them

Very tempted to just drill some holes through the damn' thing but that makes it complain as well unless you spend £lots on an ECU re-programme

I am *SO* happy that the XM is petrol

[GiveMeABreak]

Very tempted to just drill some holes through the damn' thing but that makes it complain as well unless you spend £lots on an ECU re-programme

Don't forget the likely new tests coming in to check for DPF removal 2017 /18:
http://www.frenchcarforum.co.uk/forum/v ... PF#p487852

...and it is now deemed illegal if removed (quote from Gov.UK):

"Some firms offer services to remove the filter, claiming it will improve the economy. But it is an offence to drive a vehicle that has been modified this way, as it will no longer meet the emissions standards the car achieved when it was approved for sale in the UK".