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Re: Error 2142 from ECU...

Phil, Gerard,

> Should be good for MAC11/NAC12/MAC13:
>  Audi quattro - MB engine (MAC-12) ECU wiring
                Power Stage (N70)
> 23.  Br        Inlet Air Temperature Sensor (G42)
>      Br/Red    Hall Sensor (G40)
> 24.  Blue      Hall Sensor (G40)

Pin 24 should be the other end of the air temp sensor, I noticed this
minor error when I was putting together my web page with the ECU pin
outs. Check out 

The wiring diagram you emailed me for the MAC12 shows pin 24 as having
the air temp sensor wiring. Double check this and let me know if that is

> > One final question: why would this fault show almost all the time at
> > about 115km/h doing about 3000RPM? Why occassionally at hard launch,
> > but with tacho below 3000RPM? Why, when it happens, does it go away
> > if I back of very slightly from the gas, and return when I re-apply
> > gas for some 100RPM more spin and then the light stays on until I
> > back off the gas again?

The ECU will only set the code for the knock sensor system (bad sensor
or wiring) when conditions occur where the knock sensor operation is
critical, basically above 0.7 bar manifold pressure and >3000 RPM.
(engine temp needs to be warm enough >158F, 70C). If you want to see
this "feature" in action, just disconnect the knock sensor at the
firewall connection and drive the car around. The "Check Engine" light
will go on and off as you drive around at different engine RPM levels
and manifold pressures. The timing will be retarded by ~7.8 degrees but
the engine will run. If you have an intermittent knock sensor or
connection, effectively you are driving with the knock sensor
disconnected when the ECU sets the code.

Scott Mo.
1989 200TQ