The following description, from Wikipedia, which purports to be KE, is actually a description of the K-Lambda control method; note the reference to a "fuel injector inline with the fuel return"; that is the frequency valve of the K-Lambda.
The EHA is a component of KE, is in the fuel distributor, and varies the lower chamber pressure to adjust mixture. All KEs have O2 sensing, and mixture feedback control thereby.

From Wikipedia:

KE-Jetronic (1985–1993)

Electronically controlled mechanical fuel injection. The engine control unit (ECU) may be either analog or digital, and the system may or may not have closed-loop lambda control. The system is based on the K-Jetronic mechanical system, with the addition of an electro-hydraulic actuator (EHA), essentially a fuel injector inline with the fuel return that instead of injecting fuel allows fuel to bypass the fuel distributor, which varies the fuel pressure supplied to the mechanical injection components based on several inputs (engine speed, air pressure, coolant temperature, throttle position, lambda etc.) via the ECU. With the electronics disconnected, this system will operate as a K-Jetronic system.[1]

Commonly known as 'CIS-E' in the USA. The later KE3 (CIS-E III) variant features knock sensing capabilities.

Great information guys. There is a paucity of authentic reliable information as I see it and there are possibly many variants out there. One thing I found interesting throughout all of this is that the O2 sensor never detected a fault. Yes it does light up at key on so fuse 7 and bulb are fine. The CIS-E controller is obviously failing to detect any faults and I did sensor sig open, grounded, and of course the testing above. It never once indicated a failure. Through all of this and for past 3 years I have a very good Simpson analog meter in my cabin showing the lambda signal (pins 2 and 3 of diagnostic socket) which I calibrated for duty cycle. This is how I know when I am in closed loop and O2 is active etc. I wish I had the circuit schematic of that controller but my chances of ever getting it are slim to none. Anybody have a friend in the records center in Stuttgart????

The following is a link to a KE-Jetronic technical booklet which is actually a .pdf, not a .php

So download it, then rename .pdf and it will display. Then on page 15 it shows a block diagram of the ECU and discusses its inner workings a bit.

Note that they can "add" and "take away" additional components/functions to the basic ECU. And that being an international thing, I imagine other countries might not have an oxygen sensor.

Also California cars (don't know years) do have a digital "blinky light" read out for ECU diagnostic codes [near battery] whereas with other U.S. cars, you need to use pins 2 and 3 on the round X11 diagnostic connector and read with a multimeter or a multimeter set to duty cycle %.

Save and rename to .pdf instead of .php
http://www.ferrari400parts.com/kejetronicbook.php

This was an odd failure. The role of the anode and cathode can reverse in certain battery technologies (analogous to O2 sensors) if they get damaged by a sudden current drawdown. I'm no expert but I recall this happened because of chemical changes on the anode and cathode that changed their relative electromotive potential. It's possible that the sensor cracked or got contaminated in a way that the electromotive potential changed.

Another way on a planar sensor to get funny potentials is to change the partial pressures across the sensor. If I recall right the voltage is an integral from the exhaust pressure to the sensor internal pressure so if you crack the sensor cavity and clog the exhaust side of the sensor with carbon, the backwards integral limits will give a negative voltage.

Come to think of it if it is a vented O2 sensor (atmospheric reference) clogging the vent can make it sense more oxygen in the exhaust than on the vented atmospheric side or change the relative pressure on the vented side vs. exhaust side.

I used to work for NGK sensor about 20 years ago...but it's been too long.

Actually they are both, "Digital" and "Analog"
For ecample: The analog voltage form the O2 sensor is sent to an analog input. This input is in general a "Analog to Digital converter" the converted signal is then processed by some sort of an MCU (Micro Controller Unit) similar to an CPU you find in a Computer. As you can see, the control module is both, Analog and Digital.
The reason digitizing is used, is simply because a digital signal is fairly resistant to system noise.

Dionysius, great find. Because of my electronics background, the only explanation to that would be a manufacturing defect, think you said it was only 5K in there, hope this was from this threat.
The O2 sensor has different layers of material inside, if either the structure or a reference get disconnectet inside, it is very possible to cause this result.
If it is the one with only 5K, I would try to claim money back. They are not exactly cheap.

As to procesing a negative voltage, the input has to be designed to be able to see a negative voltage. Most of those electronics components can handle about the negatve output (-1V) as decribed here. If the controller works with a +/- supply, than its possible that the firmware routine might have a so called "Trap" which would lead to the CEL. Thats somewhat odd! Although, they need a few trips to trigger the CEL.
If the output would go more negative on a positive supply only, the component would be destroyed.
So, unfortunately, nobody of us has actually a schematic diagram for the controller, we all have to guess.

I believe, what the wikipedia is referring to, is the very first fuel injection systems. Remember the ones that would work on the principal of a carburettor and the only thing that really was electronic, was the rehostat that would let a very simple analog controller know where the flap was.

I've no experience with KE, but have some with K-lambda in late 70's - early 80's Volvo where the oxygen sensor discriminator was discrete -- before Bosch custom chips used in LH and later. k-jet ecu

Best I know there was never any mechanism to recognize or deal with oxygen sensor outputs in the negative region in any Bosch system. I've experienced this on Volvos with what is a well known ECU ground circuit resistance in LH Jetronic where the two fuel rail bolts are used as power and signal ground returns respectively.

Four wire sensors and attention to the ring lugs help, but I have also had a negative output caused by contamination of the oxygen sensor's reference air with ATF being spun from a leaking output shaft seal. The Volvo documentation describes and illustrates the rear of the sensor body as the reference air sniffing location for the Bosch heated lambda sond used beginning 84-85.

I am an owner/hobbyist with a family fleet of old 240 volvos. Porkface and I go back years on this subject.:)

Cool that some people here have previously worked in the automotive manufacturing industry - like with sensors. Perhaps one of you can answer a question for me?

I'm forever looking for technical documentation and/or specifications for various electrical parts. Sometimes just the amperage capacity of the contacts on a specific relay and other times anything I can get my hands on so far as the inner workings of an engine computer...

So question: Auto parts have just a part number on the box, no electrical specifications anywhere to be found (unlike parts you may buy from an electronics supply which have data sheets available online).

Where are the electrical specifications for these parts?

Secret and not accessible to the public or something?

Or perhaps on some automotive industry web site? Automotive engineering web site?

[Everyone else in the electronics world makes this information freely available.]

Sorry, the link above had a typo.

http://cleanflametrap.com/kjetController.htm

:D

art-i was right-this is over my head. thanks for the input, chuck.

check for water under passenger seats front and back lift the carpet could foul up the connectors

Chuck, about the only thing I could add is my experience with a sensor with contaminated reference port - and I do not recall checking the ATF-soaked one with a torch flame to see if it resulted in a 1V offset as the OP found, or if the polarity was reversed. What I do remember is you and I talked about this at some length when you found some documentation to support the claim often cited that reference air is drawn through the wire strands in some Bosch zirconia sensor applications.

Anyhow, it does come up on the boards now and then about getting negative output from the sensor, but no one yet has posted as convincing an observation as Dionysus has here.

In Progress Summation................
 

Excellent responses and great references cited. We have advanced our knowledge some on this subject and we now find we are up against the fact that the unreleased information that would help is our major obstacle. Most, if not all, of this vintage of information should now be placed into the public domain IMHO. There is very little that could be considered proprietary in what I have requested re a few more levels of detail on the electronic modules and their specificity to VIN numbers. Lets face it......it would be good PR. I already stated that this event resulted in a drive critical condition. Were I in a compromising situation it could have resulted in the domino sequencing accident that Bruce Jenner just found himself a part of. In this age of more complex technologies causation will have to be analyzed much more precisely than in the past. The advent of the IOE (Internet Of Everything) will introduce many concomitant issues and we are already beginning to broach the nightmare of hacker control of vehicles. This all will get back to transparency of design information to enable causation and allocate responsibility in tort and other legal actions. Essentially an automobile is an airplane in two dimensions and the same ability to recreate and replay with data recorders will have to be made part of the design specifications and the gov agencies will have to step up to the task without screwing the whole thing up. I wish I could be part of that but I am not looking for work right now!!!!! Once again my thanks to all who have advanced my knowledge by posting here. This thread remains open.

Some tips
 

You need to call an apps engineer at a place like NGK. You need tot talk to the guy who sells the sensor in qty 100k. This is not as hard as it sounds. There are entire departments at NGK, Denso and Bosch for this. You just need to act like somebody who is designing an ECU or a car and they'll send you all the data sheets on that part. Treat it like you're an engineer who needs design info rather than a tech who needs to swap a part. For each sensor there are miles of data sheets. Call your sales engineer.