I've just gone back out in the car.
Decided to force an EGR fault by disconnecting the EGR
Started the car, got a hard P0403 code (as expected) , yellow engine MIL light and 'Have Engine Checked' message
Stopped the car, refitted EGR connector, reset the faults and went for another drive
15 minute drive with a hard P0401 fault showing in diagnostics and an EGR blanking plate in place, but no MIL light. (yellow engine light on rev counter)
The only thing I have done differently today (this is something i've done for the first time) is to monitor the EGR using the option to monitor it on the status page of AlfaOBD...shown here...egr_mon | Flickr - Photo Sharing!
When I revved the engine the P0401 code came up, and the EGR monitoring status became stuck at 'off' ....EGR position stayed at 4% continuously after the P0401 (expected)
Does AlfaOBD transmit a message to cancel the MIL of the device you are monitoring ? I don't think so because I was able to force another EGR fault. But I thought maybe someone with a blanking plate and even the free version of AlfaOBD could clear their errors and then try using this monitoring routine to confirm it ? If your MIL light stays off even when yoiu have a P0401 we will know why
I'm going to let the dpf counter increment without resetting it to see if a regen takes place with a background EGR P0401 fault.
Fireman - can you check your regen information when yoiu check the other things too please ? Since fitting yoiur blanking plate have yiou had a regen ? If not is the clogging % value very high (like a regen is due but has been deferred ?)
The only other thing which may be turning the MIL off when it should be on....if you look at the AlfaOBD screenshot which I posted a couple of messages ago you can see I also have the same throttle valve error that I discovered, when my throttle valve was full of oil (water/meth fans need to watch out for this issue)
When programmers write code and they have multiple errors to declare, it is quite common to vector multiple error precedences to that of the most important error. This means you see the most important error (the one with the highest precedence) and when you respond to it by hooking up diagnostics you will of course see the others too.
It could be that the throttle valve error (doesn't bring on MIL light) is the end vector for EGR faults. It's very unlikely, but if someone has a blanking plate and a MIL light on it is common practice to disconnect throttle valve when it is troublesome, the engine works fine (soma say better), just like when you disconnect the MAF sensor.
With the throttle valve disconnected, reset all faults and then go for a drive and see if the blanked off EGR causes a MIL.
I can't guess either way. But out of interest I would like to know if I need to fix my throttle valve or not too