The code is a piece of information.

This has to do with my wife's 2003 VW diesel Jetta, but information on this topic maybe useful for any car. I'd thought I'd ask here before I call Click 'n Clack.

The check enginel light went on about a month ago. The dealer said the thermostat was bad (from a code?), so it was replaced, and we had the coolant flushed and replaced. Now the check engine light is on again, but this time I took it to my mechanic (for my daily driver, not Boxster). He said he got "codes" for the thermstat and for the coolant temperature sensor. I had him change the temperature sensor and he reset the codes. The light is on again. So, I called the dealer and he said that if I bring the car in the code would indicate that something is wrong with the cooling system, but what is wrong would need more study. It could be the thermostat, it would be some air got into the system when it was flushed, it could be the temp senor, it could a malfuncition water pump.

So, here is the essence of my question -- I thought, maybe wrongly, that the "codes" indicate something specific. Like a thermostat, a temp senor, a water pump. I guess I thought that the level of diagnostic precision was to tell you/the mechanic precisely what needs to be fixed or replaced.

I am not a dyi guy (other than emaculate detailing), so I don't have a diagnostic kit for my Boxster or any other car. But, I'd like to know how best to handle mechanics when they talk about "codes" for any car. What do they really tell you? Something specific or a general area to look at? Or some in between level of information?

Thanks, Bob

1999 Arctic Sivler/black/black (sold)
2008s Silver/black/black - so predictable
2011 Outback
8/24/2011 first Grandson

I varies in specificity by the type of signal they are trying to analyze in the ECU and in the number of causes that such a code can point to because, as your mechanic says, they list several things and I do the most obvious and it seems to fix the problem but some codes are only learned by repeated drives of the car and you don't want to pay your mechanic for accumulating the required number of starts, stops, temperature rises and miles. I do know one mechanic who drives your car around 200 miles after he does work but that is major work and you are paying many thousands of $ for that kind of treatment.

Many parts have many codes pointing to them in some way or another. Oh, and wiring, ECU or sensor can be at fault or even something else that caused the sensor to correctly report a out-of-expected-range condition. And that is where the experience of the mechanic and his documentation and tools comes in.

Some diagnostic manuals provide multiple pages of flow charts for following a code from first reading the code to determining the cause. And many of those steps are test this, change that and see if that fixes the problem and if it doesn't, then go on to the next step.

I've used a code reader on my Porsche and my Honda. I'm far from an accomplished or experienced mechanic. But I do read online forums, I can search for where others have reported the same problem and I figure I can do some simple things until I know I'm over my head and then I call for some level of experience...either a general mechanic who has tools for simple mechanical things or a Porsche expert for more complex problems. I like to know the code and look it up before my mechanic looks at the problem. A code reader like mine costs around $80...I don;t have the most complex one because I figure I'm not using it enough to acquire the expertise to know anything beyond read code, look up code, figure out how serious. If I didn't do that, the first question I'd ask the mechanic is what exactly is the 5 digit code. It shows you know something and he guesses you'll be checking behind him.

Frequently, for older Porsches, someone will post excerpts from the diagnostic manuals in response to a "what is this code telling me" request. Don't know if that is done on the VW forums.

... for several PCA Region's Newsletters regarding the CEL.
[www.pedrosgarage.com]
Hope it helps.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

you need to take that piece and analyze with other observed facts. Basically, it can point you in the right direction.

Frequently, there are 3 or four common things which can cause a particular code. If I check the code, MANY times I can find a simple fix which cost 0 to check out. For instance, if you leave the gas cap open, even a little you will get a code. I forget the number, but if I get that code, I would immediately tighten the cap and clear the codes. If it doesn't come back, try the next thing - until it costs real money. Then I spend some thought and see if there is a way to check each issue.

In another case, my SAAB had a light which could have been a number of things -- ABS module, ABS sensors. throttle position sensor, transmission position sensor and something else. In 2 of the three cases, it was a cheap fix, but would entail huge disassembly. The other thing was an ABS module - which could be rebuilt for $50 and required four screws to remove --- easy. There were some other symptoms - the dash was acting flunky, the speedo looked weird then stopped. Both suggest the ABS module.

I swapped the ABS unit from another car. No light. $50 bucks later -- problem solved. If I did not have another module, I may have taken a shot anyway. $50 is a lot for a guess but there were supporting facts. alternatively, you can frequently bench check sensors. You need to know how to do it, but it can be done.

What you want to avoid is blindly replacing parts. Unfortunately many shops and TOO MANY diy'ers do this.

Pedro, nice write up. Good history.

I was using my wife's car as an example so that I can have some general knowledge when going to the dealer for her car, but also for future car problems when talking with mechanics. I like even simply knowing to ask for "the 5-digit code", and I can ask them what the code means. At least I might sound like I know something. I'm still at their mercy, but I can ask questions.

Still, I am surprised that the system might not distinguish between a thermostat, coolant temp sensor, water pump, or air in the system (well, maybe there would not be a code for air in the cooling system). But, I can press on those issues when I talk with them. I am going to ask to look at the computer while it is hooked up to the car. That way they are not able to report an expensive repair and just fix something that is cheap to fix. (Am I being too cynical?)

Bob