The 986's Check Engine Light



 CELs on the Boxster

The CEL can mean a hundred things. Generally, it is a external warning set by the Engine Computer (DME) or Transmission Computer that something is wrong and the DME stores secondary “codes” that can be read by a mechanic to tell the mechanic what is wrong.

First, if the CEL is blinking, stop the car, stop the engine and get the car flatbedded to your favorite mechanic.  Blinking CEL means something serious and further running could damage your engine $$$$$.

You need to know the secondary codes to know what the cause might be. Fortunately, on every US car built after 1995, there is a standardized diagnostic port that will allow a readout of more diagnostic information in the form of 5 place codes. On the Boxster, the port is located over your left knee when sitting in the drivers seat.

I use an Actron CP9135  ( (generally about $100 to buy it) to read and reset codes.

But you can also get the codes read at some auto parts stores (AutoZone is said to do it for free, likewise Pep Boys).  They will have generic readers, the equivalent of the Actron I mention.

There are many other brands and models of readers.  They plug into a OBD II (On-Board Diagnostics Version 2) port above the fuse/relay panel just above your left knee (US cars).

There is also software and a hardware adapter available for ~$250 that loads onto a Windows  XP laptop. If you are buying for lots of different make cars, the Actron may be better.  Just for the Porsche, the Durametric software is  superior if you have a Windows XP portable with the USB connection. The Durametric can access codes the Actron can't.  But you can't beat the Actron's portability. Note that the Actron can read an infinite number of post-1995 model years cars while the Durametric has 2 versions and the cheaper will only read codes for 3 Porsche cars.

To find out what the codes mean on a Porsche, the best list is available for free on Look under the “Online Docs” button on the top right of the page for “OBCII P-Codes”. You need to look at the DME Engine Codes for your Car Model (Boxster 986) DME 5.2 for years 1997-1999 and DME 7.2 for years 2000-2004.

Be aware that there are codes that the Actron can't read that could be helpful in diagnosing a problem that a Porsche System Tester 2 (PST2) or the later PIWIS can. Dealers have these system tester and some independent mechanics specializing in Porsches have them.

There are multiple thick volumes written about how to diagnose a problem that your dealer has (The multi-thousand dollar multi-volume maintenance/repair manuals). Often the codes can have multiple causes. The dealer (and some independent mechanics) have multi-volume service manuals, PST2 code analyzers and additional diagnostic tools. The service manuals give the equivalent of flow charts to show how the mechanic should test to further isolate the real problem from amoung the many possibilities. That the same code can be caused by several causes explains why, in forums, you can get people asserting that their fix is the right one for your codes when someone else is equally sure the codes point to a different cause/fix.

But the Actron and its ilk are good enough to read the major codes and clear many of the CELs.

Once you know the subcodes, search for them on one of the online forums specializing in Boxsters (PPBB ("search the archives" function) or RENNTECH) and you'll often find explanations, diagnostic tips and even do-it-yourself instructions. 

If you then have to pass an emissions inspection, it may take some time (starts) and some miles after the fix and codes reset before the computer will report no codes to the emissions inspector.