Sensor Specifications

[Bohdan L Bodnar]

>The following describe the sensors on my '87 Fiero, from other 
>experience with GM products I would expect these ranges to be 
>typical of most product from GM.
>
>TPS - This is a potentiometer between gnd and +5 volts.  Output 
>ranges from ~0 at closed-throttle to ~5v at WOT.  Closed throttle 
>offset from 0 is not critical as the ECM "learns" where closed 
>throttle is.
>

Close, but not quite.  Closed throttle voltage is around 0.5 to 0.6 volt.
Anything lower than this will set a diagnostic trouble code ("TPS shorted to
ground").

>CTS and MAT - These are voltage outputs from bridges in which a 
>negative-tempco thermistor is pulled up to +5 volts.  Resistance of 
>the thermistor ranges from hundreds of k-ohms in the cold to hundreds 
>of ohms in the hot.  to complicate matters, my Fiero switches the 
>value of the pullup resistance once the coolant temperature exceeds 
>about 100 degrees to widen the temperature range where the bridge 
>scale factor (volts/degree) is large enough to use.  Output is VERY 
>nonlinear, but so what, I assuem the ECM has a look-up table.  I have 
>calibrated the sensors on my Fiero and can give you some details if 
>you're interested.
>

This is done to limit analog-to-digital converter quantization error (similar
to mu-law and A-law companding in telecommunications).

>MAP - Outputs a signal which ranges from~0 to ~+5 volts. Pontiac has 
>used (at least) two different MAP processors in the past, for one 0 
>volts corresponds to atmospheric pressure, in the other ~5 volts 
>correpsonds to atmosphere.  My Fiero uses the second type MAT 
>processor.

Partially correct.  ALL GM MAP sensors which are not used with a turbocharged
engine will output something close to 5 volts at atmospheric pressure.  If
used with a turbocharged engine, a different MAP sensor is used -- its output
is 2.5 volts at "atmospheric" pressure.  The second type of sensor you're
referring to has two vacuum hose connections to it:  atmosphere and intake
manifold;  the output corresponds to the difference between the two pressure
signals.  I don't remember its name right now (MUCH too early in the
morning).
>
>O2 - A very high impedance source that ranges from ~-0 volt when lean 
>to ~1 volt when rich.  Output characteristic makes "step" transition 
>from 0 to 1 volt at ~stoichiometric ratio.  Look at the archive for 
>this mail list for thorough, and good, discussion of the O2 sensor 
>operation.
>
>
>John
>