Porsche Boxster 986 engine control light, too lean mixture and lambda sensor from cat. Bank 1 to Cat. Bank 2

  • Hello dear members of the forum,

    I am facing a problem with my 2002 Boxster 3.2l switch.

    About a week after I bought it, the engine control light (ECL) came on and the error "Lambda sensor after catalytic converter bank 2" was displayed. I replaced the lambda sensor and drove on for about 500 km, when the MKL appeared again. This time it also showed errors for bank 1 and bank 2 before the catalytic converter.

    My Porsche mechanic checked this more closely and found that the original catalytic converters and manifolds had been replaced by sports accessories (fan manifold and sports catalytic converter). However, the rear silencer comes from Porsche (flap exhaust).

    His diagnosis is that the entire exhaust system, apart from the rear silencer, needs to be replaced and it would be best to use original Porsche parts.

    The mechanic explained that the mixture was too lean and that this could be due to the exhaust system.

    Now my question to the Porsche community: What do you think about this? Do you have any inexpensive suggestions for replacement catalytic converters? The costs at Porsche amount to 2400 € for the catalytic converters and 1200 € for the manifolds. Could the lean mixture be due to the exhaust system?

    Incidentally, the lambda sensors work perfectly and the catalytic converters do not clean the exhaust gases.

    Can I continue to drive with a mixture that is too lean, or could this lead to consequential damage? The engine otherwise runs perfectly. :hilferuf:

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  • Hello,

    Welcome to the forum.

    The message with the lambda sensors has already been described several times, the reasons for this can be different, also look for 996 or 997.1, which have the same engines. But what I can already say is that you don't need to replace the exhaust and your mechanic is suggesting the simplest and most expensive solution for him, presumably because he has no idea. k:facepalm: Did he actually read the messages with a PIWIS? Or at least durametric?

    Here are a few suggestions:

    • Lambda sensors sooted up, blow through on the track after warming up.
    • How many tkm does the Boxster have? Possibly worn Variocom pads? Are the Variocam solenoid adjusters clogged/defective? Can be easily determined by a deviating ignition curve when the engine is running.
    • Is the mass air flow sensor working correctly or has the intake manifold been modified?
    • Is the intake manifold seated correctly?

    .....etc. etc.....

    :pfeil: Find a freelance professional for Porsche, preferably in your area. There are a few here in the forum, even in the banner ads.



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  • Hello tkm,

    thank you for the detailed answer.

    I forgot to mention an important fact, hence the addition; the boxster does not clean exhaust gases, the mechanic put a sensor in the exhaust and the values showed that the lambda sensors work, but the HC value is much too high because the catalytic converters do not clean or do not work.

    About the boxster, it has run 178tkm and got a replacement engine at 40tkm, so the engine has run 130tkm.

    VG and have a nice Sunday :thumb:

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  • To add, the intake manifold is tight and fully intact.

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  • Hello,

    yes, that was really important to know. In this case, does sport cat mean that it is empty? If so, you need new catalytic converters, 200 cells with test mark, if you don't want to have the map adjusted. However, there are people here in the forum who have already done this on the 986 and therefore have more experience than I do with my standard silencers on the 996.

    What can also be a problem at 130 tkm are the Variocam pads, or the Variocam solenoid adjuster, see above. Start here:

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  • however, the HC value is much too high

    this is poor incomplete combustion. There's nothing the cat can do.

    How long have you had the vehicle, warranty still available, private purchase perhaps still feasible.

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    Porsche Boxster 981, Bj. 2012

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  • Hello FrankV8,

    according to the mechanic and others, a too high HC value is due to too many exhaust gases and thus the lambda before the cat tells the engine that it should get less fuel because the exhaust gases are too high :wink:

    Does that sound plausible to you?

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  • A high HC value means unburned fuel in the exhaust gas. It is logical that the engine control unit then reduces the mixture. Now you just have to find out where the fault lies. What are the values left/right, before and after the catalytic converters?

    If your workshop doesn't come up with anything else apart from replacing almost all exhaust-gas-carrying parts, well, that's your decision. But it has nothing to do with the high HC value.


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    Nach 320'000 Spiegeleiern kann die Kantine nicht so schlecht gewesen sein!
    Harm Lagaay

    PS: Ich heisse nicht Greetz k:thinking:

  • First of all I would change the plugs, if they are old the combustion is bad- theHC value increases-

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  • Hello everyone,

    Many thanks for the numerous answers and tips.

    So you don't think that if the catalytic converters are defective, they would have to be replaced because the engine gets a mixture that is too lean?

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