EGR dash light, how does the ecu know?

d4v1d sm4rt

A2OC Donor
Just thinking about installing a modified straight through EGR valve ( with a non shudder valve still in place ) and I have heard that it will put the Engine light on but as I have not done this I have not experienced it. So I was wondering how does the ECU know that you have blocked off the pipe that recycles the exhaust gas from the manifold back into the inlet as all there seems to be is a vacuum operated valve. Does the ECU monitor the momentary drop in vacuum from the actuator solenoid and then deduce that the valve is operating because it is seen to have used some of the vacuum stored? If this is the case then maybe you could just run the vacuum pipe to a dummy vacuum valve?
And if you just block off the vacuum pipe does the light come on? And if so,why?
 
i will happily be corrected if i am incorrect, but there is no sensor as suck on the egr to monitor its use/performance, but the car knows when is should be open and how much gas should be recirculating. It uses the MAF to calculate this. Ie, Air expected in engine (minus) air measured through MAF = amount of gas passed through EGR
 

wilco184

Member of the year 2015
Hi David,

I am unsure as to details regarding the BHC and ATL engines, but if you have an AMF engine and blank off the EGR valve, I can confirm that no engine light comes on and no issues are to be reported. This is with a physical blanking plate in the EGR corrugated pipe, and not a blocking of the vacuum hose; but the results should be the same.

Thanks,

Matt.
 
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And if you just block off the vacuum pipe does the light come on? And if so,why?
Hi,

Petrol or diesel?

On a petrol there is a potentiometer built into the EGR valve to let the ECU know how far the valve is open - can imagine the ECU will know if this feedback is missing.

"Audi self study programme 247" covers just do a search online
 

d4v1d sm4rt

A2OC Donor
It's diesel so no potentiometer
Hi,

Petrol or diesel?

On a petrol there is a potentiometer built into the EGR valve to let the ECU know how far the valve is open - can imagine the ECU will know if this feedback is missing.

"Audi self study programme 247" covers just do a search online
 

Valentin

New Member
Hello, i remove today my Egr valve ( 1.4 petrol engine) and clean it.What i find strange is the vacum part of the Egr seems not to work,the vacum is doinig nothing to the Egr, no resistence if i apply suction to the small pipe.
Electrical i test it with Vcds an works. It is normal? What is the porpous of the vacum line to the EGR?
 

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Howey

Member
i will happily be corrected if i am incorrect, but there is no sensor as suck on the egr to monitor its use/performance, but the car knows when is should be open and how much gas should be recirculating. It uses the MAF to calculate this. Ie, Air expected in engine (minus) air measured through MAF = amount of gas passed through EGR
Spot on!
 
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