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VWDoc
VWDoc, Independent VW Shop owner
Category: VW
Satisfied Customers: 6456
Experience:  20 years of experience working with VW's. Independent European shop owner and technician.
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2002 VW Jetta: Ltr..Turbo..My chec engine light came on and I..tire

Resolved Question:

I have a 2002 VW Jetta 1.8 Ltr Turbo that runs only on premium fuel. My chec engine light came on and I found a loose sensor cable underneath the front passenger side in front of the tire. The car shifts rough too. Where does the sensor cable attach to? It's round.
Submitted: 5 years ago.
Category: VW
Expert:  VWDoc replied 5 years ago.

VWDoc :

Hello, I'm Jason. I will do my best to answer your question quickly and accurately using the information you have provided.

VWDoc :

there really aren't any engine sensors in that area. Any chance you could take a picture of the cable and post it here?

VWDoc :

and ideally, it would just be best to have the engine computer scanned to determine the codes. I can help quite a bit more if I had those

Customer:

Where would I have my Engine Scaned? Autozone?

VWDoc :

They could certainly do that, yes. I would need a full list of the Pxxxx codes, and please do not allow them to sell you the parts that they think might fix the problem, as they're not trained for such things

Customer:

I'll take a picture and post it.

VWDoc :

perfect. Right now, it sounds like the passenger marker lamp bulb connector, but we'll see

Customer:

That's what it looks like. But, would that mae the engine light come on and shift rough?

VWDoc :

no it would not

Customer:

That's what it looks like. But, would that make the engine light come on and shift rough?


Customer:

Guess I'll have to schedule a trip to the nearest dealer which is about 40 mikes away. Thx!

VWDoc :

well, again, the dealer isn't the only option

VWDoc :

if I had a code list, I could likely tell you what needs to be done

VWDoc :

and I would suggest a European/VW independent shop over a dealer

Customer:

I'll go to Autozone and get it scanned. But, I need to mow the yard. I'll get back with you later.

VWDoc :

lol....as do I (the yard)

VWDoc :

I'll save this and I'll be alerted when you reply

Customer:

Dang thing grows like crazy.

Customer:

ok, later.

VWDoc :

Also, this will revert to a question/answer email format rather than chat...

VWDoc :

but I'll still be alerted when you reply

Customer: replied 5 years ago.
I have the following Diagnostic Codes PO171, P0420 and P0442. Two of the three say oxygen sensor.
Expert:  VWDoc replied 5 years ago.
Ok, first the descriptions, and then my recommendations

P0171 16555 System Too Lean Bank 1

P0420 16804 Catalyst System Efficiency Below Threshold Bank 1

P0442 16826 Evaporative Emission System Leak Detected (small leak)

Right now, it actually looks like you have a few separate problems, but let's concentrate on the one causing the running problem. That's the P0171 code. On these cars, they're very suceptible to intake air leaks. In some cases, this is caused by a faulty air mass meter, but I've seen far too many cases of air mass meters being replaced, not fixing the root problem. The best and most accurate method of determining if you have an air leak, and the location of it, is to have the intake system pressure tested using a smoke generator. Most good diagnostic shops will have this capability. Let me show you an example using my smoke machine and the same engine you have in your car.

graphic

You'll see the smoke generator in the center, the intake air hose capped on the upper right, and the smoke hose in the lower left to introduce smoke into the throttle body.

One common leak area is here:

graphic

Often, other leaks are found near the rear of the engine, either at the turbo diverter valve hoses, or other pressure hoses.


Now, let's talk about the P0420 code. This is a catalytic converter efficiency code that will likely require converter replacement, however, wait to do that until you get the lean running code fixed, then turn the light off, and see if the code comes back.

And finally the P0442. This is a fuel vapor leak, which can also be tested using the same smoke generator, but this time on the tank and related vapor systems. I've seen many cases of the vapor purge valve hanging open slightly. I'll show you a picture of this as well.

graphic


However, none of these codes indicate to me that oxygen sensor replacement is necessary.
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