Differential pressure sensor location?

Jimbo70

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2003 Jetta. I have a chronic "16785 - EGR System: Insufficient Flow" code. I replaced the EGR (it was plugged solid) but the code continues. the Ross-Tech Wiki references the differential pressure sensor or the EGF-DPF sensor. Where would I find this sensor?

Thanks,
Jim
 

Jimbo70

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Anyone, anyone, Buehler? I checked the new EGR to make sure it wasn't clogged again (it wasn't) and I hooked up a vacuum pump to the EGR diaphragm to "exercise" it. No CEL today, but I believe this car has gone days without a CEL before.
 

oilhammer

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Follow the vacuum hose from the EGR valve up to the firewall, where the little pressure valve lives.

It is however much more likely that your MAF sensor is sending an improper signal. The ECU uses the MAF voltage to monitor EGR flow. The ECU opens the EGR and looks for a certain amount of voltage change from the MAF. If a weak MAF cannot produce that voltage, the ECU can assume the EGR is not functioning when in fact it IS but the MAF is not.
 

Jimbo70

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oilhammer said:
Follow the vacuum hose from the EGR valve up to the firewall, where the little pressure valve lives.

It is however much more likely that your MAF sensor is sending an improper signal. The ECU uses the MAF voltage to monitor EGR flow. The ECU opens the EGR and looks for a certain amount of voltage change from the MAF. If a weak MAF cannot produce that voltage, the ECU can assume the EGR is not functioning when in fact it IS but the MAF is not.
Thanks for the info, Oilhammer. Interesting, I just replaced the MAF with a Pierburg in February; only 8k miles ago. I replaced it about the same time I replaced the MAF in my Golf (matching cars within 5k miles of each other; double your pleasure, double your maintenance bills.) I'll take a look at the lines that go into that little pressure valve. My wife has reported no CEL since I worked on the car on the 4th. Perhaps the new EGR was stuck closed and "exercising" it with the vacuum pump popped it loose?

Jim
 

Jimbo70

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It took a week, but the CEL is back on. I'm really stumped at this point. Could the new MAF be bad already? Did I read somewhere that the MAF can be cleaned?
 

2004STARWARSTDI

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Cleaning MAF

Jimbo70 said:
It took a week, but the CEL is back on. I'm really stumped at this point. Could the new MAF be bad already? Did I read somewhere that the MAF can be cleaned?
Yes there is a spray cleaner used to clean MAF.:) You aren't using a K&N or any "oiled" air filter-right?:confused:
 

Jimbo70

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We are not. This car is completely stock. The next time I have a moment I'll clean the connector. Should I also clean the sensor itself?
 

Jimbo70

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Update

I VAG-COMmed the car today and the good news is the EGR did not cause the CEL. The bad news is that I got the dreaded 17656. I hope that it is a matter of the roll pin in the case differential regulator coming out again. If it is I think I might put a drop of Crazy Glue or some Locktite on the roll pin before puting it back in.
 

Jimbo70

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Three months later, the 17656 timing issue has been solved, but the 16785 EGR Insufficient Flow problem has not. After reading about the Pierburg MAF in the FAQ, I purchased a Bosch unit and installed it. No dice.

One thing I neglected to mention (mainly because I forgot about it) is that I did attempt to recalibrate the EGR after replacing it and having the intake manifold cleaned. I'm going to take another crack at that when my wife gets back with the car.
 
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