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The malfunction indicator light on my Jetta dashboard has been going on for the past 6 months. I have taken it in to the shop at least 6x but the problem is never resolved. I have had a new catalytic converter put in, and yesterday a new thermometer but the light is on again! When the mechanic scanned for faults, four appeared: a problem with the cooling system, 2 faults with cylinder misfire, and one with converter efficiency. My mechanics solution was to replace the thermometer, but clearly this was not the solution. This morning he tells me that Jettas this age are "just finicky" and that it would be the same if I took the car to the dealer.... What do you think the problem is? Is it true that this kind of problem cannot be diagnosed? If I have to take the car in every second day, I will have to sell it - but 2003 does not seem that old to me.

Answers from the Automotive Experts

Amanda J. Pierce, MBA Mary Allen, Thank You for writing into AskPatty!! To address your concern with your 2003 Jetta, in my opinion there is no issue that can not be diagnosed. We just need to do a series of 'reason of deduction', (1) your cooling system fault code MAY be related to the Coolant Temperature Sensor (CTS), this is a sensor that tells the main computer (ECU) the perimeters set by the manufacturer. If this sensor malfunctions it CAN throw a code causing the check engine (MIL) to kick on. (2)& (3) Cylinder misfires can be caused by a few things such as; spark plugs that need to be replaced (Always couple this with replacing your spark plug wires as well!) Also, you may have a coil pack that generates that spark have a malfunction. If it has been over 60-75k miles I recommend have your plugs and wires replaced. (4) Converter inefficiency may be due to an oxygen sensor (O2) that may be malfunctioning. Hope this helps!! A. J. Valle

Judy Curry, Co-Founder and Vice President of Marketing at Currys Auto Service Hi Mary Allen! Any problem can be diagnose given enough time money and equipment, with a qualified technician. Depending on mileage one can assume the cat was damaged by the misfire. The misfire could be from ignition coils, spark plugs, vacuum leaks and or engine mechanical issues. A smoke test , compression test and cylinder leak down are in order to determine the engines ability to perform the needed mechanical task of internal combustion. If all that tests good then a scanner and oscilloscope would be used to read any affected sensors and or ignition coils to determine their ability. I am sure in the correct and capable hand’s this car can be restored to normal function in no time. Be patient and find a trusted technician who will take the time to get to the source. Good luck!

Kristin Brocoff, Director of Corporate Communications at Intermittent "check engine" lights sure can be frustrating, but with the average age of a passenger vehicle fast approaching 11 years, you should have a few good years left with your 2003 Jetta. I highly recommend that you get a second opinion from an ASE-certified techician or the CarMD Vehicle Health System. With more than a half million repairs in its database, when you get a diagnosis using the CarMD handheld device and software program, it's like getting a second opinion from thousands of trusted mechanics. You can also visit to see the most common problems for your year, make, model and mileage, but I would never recommend replacing parts based on just a guess or a trouble code. You may also wish to see if your car has any known recalls or service bulletins that may be associated with the problems you're experiencing. They can often help diagnose a finicky problem, and sometimes can even result in free repairs. Best of luck to you! Kristin Brocoff, Corp.

Lori Johnson, Owner and Instructor at Ladies Start Your Engines Dear Mary Allen, At this point I would have to say that your technician probably is not diagnosing the problem correctly. I would recommend that you take it somewhere else and probably the best place would be the dealer. You may find that a dealership knows what the problem is right away because they know the vehicle. Many people complain that dealers are too expensive, but one trip to fix it right is better than many trips and paying for things that don't fix the problem. And I've never been of the belief that a problem can't be fixed. Lori Johnson

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