My 93, 3.2l keeps getting a code for the EGR valve system. The code is 32. Which according to the book is " EGR system failure". How is the ECM determining a failure? There is no sensor on the EGR valve itself. The EGR valve is clean and I seem to have good flow from the tube feeding it. So, I ask again what is indicating to the ECM, that there is a problem with the EGR?