How is egr monitored - 406 2.0 Hdi 90 hp Siemens

[Lee1978]

Hi all. As per the title, I'm wondering how the ecu monitors the egr flow? I have a P0402 fault code and here's the strange part, it comes straight back after deletion, even with the engine off!
The fault code seems to relate to a stuck open egr which is stranger still, mine's blanked off!
Obviously this is an electronic issue but I can't think what the problem might be.
As always any help is much appreciated.

[gumby6371]

Have you had the EGR mapped out?

I have read that on some cars once they're removed from the map you shouldn't leave the electro valve plugged in to the wiring harness.
Not 100% this applies to the 406 with a Siemens set up tho, my Bosch doesn't care plugged in or not.

[Lee1978]

I expected to need the egr mapping out as I read the Siemens 406's do require that, however I was lucky and didn't get the eml. I left everything plugged in and just made a blanking plate for mine.
I read the fault codes just out of curiosity and found the P0402 fault code lurking in my ecu which as far as I can tell doesn't relate to the egr being blanked off, quite the opposite, seems like that code indicates the flow is too high like it's stuck open.
I'm not sure what these 90hp cars are supposed to run like but mine is one of the slowest cars I've ever driven, I wonder if there's something wrong with it!

[Lee1978]

I know some cars rely on a differential pressure sensor accoss the egr to determine flow but I'm pretty sure that's not our cars. It's my guess our egr is monitored by regular sensor data, maybe the ecu notices the engine takes less air when the egr is open?

[rwb]

I had the EGR blanked on my Siemens 90 with no problems. The best way to do this is to pull and bung the vacuum supply to the solenoid valve (assuming of course that the EGR valve itself isn't stuck open). You must leave the electrical connection of the EGR valve plugged in.

The system can tell that not enough air is being recycled because the MAF reading is higher than expected. This always causes a fault, but does not make the EML come on. (The situation is the same on many other models, including ones with Bosch ECUs.)

So: if it's the air flow too high error then with a blanked EGR that's normal.

There are two parameters for the EGR that you can measure in PP2k: the requested position and the actual position (known as position repeat). The EGR unit measures its actual position and reports it back to the ECU. If it's far off the requested value then aunty polution is summoned.

[Lee1978]

Rwb, thanks for that info, exactly what I was looking for! The strange thing is I don't have to run the engine for the fault to return, I wonder whether the maf is reading artificially high and the ecu has got confused, shame I haven't got pp2000 to get some realtime values. I think, considering I've had this car for around 5 years and have no intention of getting rid I better invest in pp2000