Sensor Specifications

[John T Stein]

On 8-10, Thomas Ennis Bragg Jr wrote:
> 
> Where would I be able to find technical specifications on GM sensors
> like voltage and current levels, etc?
> 
> I need this info for TPS, CTS, MAP, MAT, O2 from an 87 Pontiac Sunbird Turbo.
> But any info would help out.
> 
> Thanks
> 
> Ennis
> -- 
> Ennis Bragg	
> gt9803a at prism.gatech.edu
> 
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.

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.

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.

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