Wide range lambda sensor

[Ludis Langens]

Here's some info about the Honda sensor gleaned from a troubleshooting
and repair manual:

One position of the 8 pin connector isn't used.  Two positions go to
[each end of] the heater element.  These are not connected to any of the
other wires.  Another two positions go to [both ends of] the calibration
resistor.  These also do not connect to any other wires.  The last three
connections go to the sensor/pump elements - one to a common junction,
one to the sensor, and one to the pump.

None of the five calibration and sensor connections are interconnected. 
Also, none of them are grounded or connected to a constant power
supply.  The expected voltage range at any of these points is probably 0
to 5 volts.

The heater element seems to be operated on 7 volts.  One end is grounded
via the wiring harness.  The ECM sources 7 volts into the other end.
This is different than all the other Honda HEGO applications.  The other
HEGOs are all connected to the battery voltage (nominally 12 volts) with
the ECM sinking to ground, presumably to measure the current to set a
malfunction flag.

The resistance specs for the heater, compared to regular HEGOs, confirm
that it should be run on something like 7 volts.  (Assuming that all
heaters need to be about the same wattage.)  I can only come up with two
possible reasons for the 7 volts:

  A high power quick heatup cycle.  However, the trouble shooting flow
  chart did not attempt to exclude any such cycles when checking for the
  7 volts.

  A need to have a fully heated and operating sensor even during
  cranking and when the battery is very low.

A caution: the troubleshooting guide did not specify how each circuit
was supposed to operate.  It merely listed the minimum number of checks
needed to identify the bad component.  Deducing the operation required
reading between the lines.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/