03' passat 1.8T CEL codes


ok, car runs rough until blower fan turns off (for turbo?).

Codes are as follows:

PO 302

PO 303

PO 304

PO 3D1

PO 300

PO 171

We have new plugs and I think it is the O2 sensor. ($$$)

Any other good ideas before I take to dealer or indy? Appt with dealer is 20 June…


P0302 ? Cylinder 2 Misfire Detected
P0303 ? Cylinder 3 Misfire Detected
P0304 ? Cylinder 4 Misfire Detected

P03D1 ? Code not found
P0300 ? Random Misfire Detected
P0171 ? System Too Lean (Bank 1)


My guess is that the PO 3D1 is really PO 301 and you are having an ignition problem. However that does not identify the cause of the problem. It could be wires. They don’t last forever you know. But there are a few other possible causes as well. Changing out wires it cheap and easy.

Now about going to your dealer for non-Warranty work:

    Dealers are no better (or worse) than independent mechanics for almost anything you might need done on your car.  They will almost always charge more per hour and often more for parts and supplies.  They also tend to look at repairs a little different than the independent. 

A dealer may well recommend work that strictly may not be needed, but could be connected to the problem or maybe replace a part when a little repair would fix it ALMOST as good a new.  

There is no need to bring your car to the dealer for any service other than service that is going to be paid for by a recall or original warrantee. 

I suggest that most people would be better off finding a good independent (Not working for a chain) mechanic.


[b]I don’t believe there’s a problem with the O2 sensor. If there was, there would be a code indicating so.

All these codes indicate random misfires in all cylinders, and a lean condition in all cylinders. Which would cause the misfires. So what needs to be done is determine as to why the engine is running lean.

Things to check are a dirty fuel filter, weak fuel pump, vacuum leak somewhere on the engine, and an exhaust leak prior to the #1 O2 sensor.

Also, the Mass Air Flow sensors used on the VW’s of this year were notorious for failures. And when these failed, it could set all the codes you listed.



The shop manual for my 02 Hyundai Sonata shows 10 possible causes for the PO-3XX codes. One of them is “Vacuum leak in air intake system.”

For the PO-171 it lists 7 possible causes. One of which is “Vacuum leak in air intake system.”

As Tester sez take a look for a possible vacuum leak.

You might get lucky & solve this one yourself.


Dealer replaced Mass Airflow Meter - Covered under Warrantee :slight_smile:

Part on GermanAutoParts costs 225$ alone.