EGR flow I think is measured between MAP and MAF sensors. Due to the turbo, the MAP should always be higher than MAF sensor. If EGR valve is open, this should boost the MAP reading higher than the MAF. This is due to the turbo able to spool more since the exhaust is recycled. That is the only way that the EGR flow codes can be triggered with the sensors available on the ZD30DDti CRD. MAP is the sensor on the intercooler.
The ECU relearn may reduce the ECU's sensitivity between MAP and MAF. Not saying it will stop it but if it was expect a lot of EGR flow before and now there isn't, the ECU will throw an error. If ECU isn't expecting much of a difference, it will be harder to throw the error.
The reason its variable is due to all the circumstances the car can do through. If you live higher than sea level, oxygen levels are going to be different and the expect variables will change. If it gets ridiculously cold, the oxygen is more dense and fuel mixture will need to be adjusted. Change exhaust? New intercooler? Different turbo?
These variables are held in the ECU as long as there is power. This is remembered for when you next switch on the engine so it can run at optimal settings.
Edit: I wouldn't know exactly. But if I was told by my boss that we had a checkbox to tick - "Identify when EGR is tampered as cheaply as possible" - I would do the above. IT person by trade. I just get into the heads of engineers on what they would do.
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Originally Posted by stewc1986
