Mystery engine light

I have a 2001 New Passat GLS 4-cyl. 1.8L. 61,000 miles.

The engine check light has been on for 6 months. I have had 3 diagnostics run. Each time they find small fixes(faulty jet pump valve, vacuum hoses etc)but otherwise, it looks good. The light goes off, but with in 48 hours, the engine check light is back on again. There has never been any performance issues; the car runs fine. I am hesitant to go back to the dealer because they’ll keep charging me. So what to do? The car runs fine. Do I ignore it? Could it be a fault in the engine light somewhere? I didn’t get my 40K check up at the dealer, could it be set for that? Help solve the mystery of the light that would not shut off!

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

The “check engine light” is set by things that, negatively, affect emissions. Go to an auto parts store and have the scan done. Bring the codes, including the freeze frame data, and the incomplete monitors list, here for review and advise.

Thanks. Went to AutoZone and came up with the following code: P0171. Says the fuel system for bank 1 was too lean. Suspects: 1) fuel pressure or MAF sensor. 2) Oxygen sensor defective. 3. Ignition misfire 4. Fuel injector problem.
Given that this car has been through a few diagnostics with little or no results and the CEL keeps coming on, any recommendations?

Here’s a list of things that can cause this code, and possible solutions to correct it.


The first thing you should be looking at here for a P0171 “Bank 1 Too lean” on a Passat is a broken vacuum line. On a 2001, you are due for replacement on all of them as they tend to dry rot. You need about 15 feet of 3.5mm line. Pay particular attention near the turbo (they dry rot there because of the heat), and in areas where the line goes into a fitting.

Once all your vacuum lines are in order, and if the code returns, look at the Mass Air Flow sensor. It may need a cleaning. Remove it and stick it in a gallon ziplock bag with some rubbing alcohol, shake it up till the fluid is nice and dirty, and set it out in the sun to dry for a couple of hours.

This is the easy stuff. If it still doesn’t go away, have your mechanic make sure the MAF sensor is operating within spec.

Like David Letterman’s Top Ten List, I will give you my shorter list of things to do, starting with the most likely problem first.

  1. Check for any air leaks on the bank 1 side of the intake and exhaust systems.
  2. Clean the MAF sensor using the proper cleaner.
  3. Get a bottle of Techron and pour it into the empty fuel tank to help clean the injectors.
  4. Check the bank 1 O2 sensor out for a problem.

Hopefully by doing one of these things it will correct the problem but there are other things that may be the cause of this trouble.

Great site.