Originally Posted by slk230red

I see you are in California, doesn't your car have the built-in LED and button on the Diagnostic Block in front of the battery?

@1988 California and
@1991 with diagnostic trouble code
storage:
The CFI control module must be switched over
to output of on/off ratio because the signal for
the diagnostic trouble code (DTC) display is
output as priority.
The output of the on/off ratio is performed once
all the DTCs have been read out and the start
button of the impulse counter scan tool or the
non-locking switch on the diagnostic connector
(California version only) is then once again
pressed (see section m).
The % readout now fluctuates when the engine
is running at normal operating temperature and
there are no DTCs.

On/off ratio
in %
Possible causes of fault
- No voltage or ground at diagnostic connector (Xl 1)
- Cable from diagnostic connector (Xl 1) to CFI control module (N3) has open
circuit
- Lambda control tester defective
- Mixture setting too “rich”
(on/off ratio 0 - 8 % also possible)
- @ California model year 1988 and @ 1991: CFI control module not
switched over to on/off ratio output.

Originally Posted by socaleuro

Never even tired looking for that LED and button by the battery. When I do find it, all that is reguired is to turn the key to the 'on' position and then press the button for 2-4 seconds and record the pulses, correct? After that I should be able to read the lambda @ pins 3&2 of the X11 connector if everything is all good?