Knock Sensor Question

[Dan Dwyer]

I've been playing with the boost in my '89 200Q.  If I go too high with the
boost, I get a check engine light above 3800 rpm.  When I check the error
codes, I get an error code 2142.  Investigation on SJM's sight gives the
following explanation for the error code:

    2142
    Knock sensor #1
    Open or short circuit, Defective sensor
    Check sensor and wiring
    Symptom: Timing retarded, High fuel consumption, power loss, Boost
pressure not attained

I can drive the car forever and not get the above error code if I have stock
boost.  My question is, if my knock sensor is bad, how come the computer
only realizes it above stock boost levels.  The higher boost could certainly
cause knock, but then wouldn't I get the following error code if that was
the case:?

    2141
    Knock regulator #1
    Excessive knock, timing is being retarded by maximum amount 7.8 degrees,
Low boost on 20V,
    Fuel octane too low, Excessive Compression, excessive boost

If anybody can help me to understand if I have a problem with engine knock
or just a faulty sensor I would appreciate it.

TIA,


Dan