Some of what I am about to tell you may be partially true.
A LITTLE insight- the long version. You noticed a previous poster made reference to the sensor with 4 wires rather than 2. In the MY98 engine control the upstreams were 4 wire heated zirconia lambda sensors while the downstream sensors were non heated zirconia type. By MY 2000, the upstreams changed to wideband sensors and the downstream changed to 4 wire heated zirconia. I am not fully aware of the technology used for the widebands, but the schematic clearly shows the sense circuit on them being entirely different to the ecu. The heater circuits seem to be the same for all 4 sensors.

The main difference in the sense circuit is that the downstream sensors have the negative side connected directly to ground and the "sense" side brought into the ecu. The upstreams (wide band) have the sense and negative side brought into the ecu, implying that the negative side is not grounded. That is consistent with a low voltage signal the engineers wished to sense very accurately, as I ASSUME the wide band signal is, being bought into what is called a difference amplifier.

Your measured data SEEMS to be consistent with the diagram so far. So lets interpret your data. For the downstreams, the sense ground is ground as the diagram says, the sense is also 0 or ground also - meaning the sensor detects a lean condition. Since it should be constantlyswitching betweeen .2 to .8 volts, that is not necessarily significant. The power to the heater is 14, as I previously told you, and the heater negative lead to the ecu is being regulated by the ecu to have 2 to 7 volts across the heater. (14-12 or 14-7). That is all consistent with what I would expect.

Now, the upstream circuit. The heater controls are not calling for heat from either sensor. Or the heater controls have a broken wire between the sensor and the ecu. No current is flowing thru the heaters since the voltage drop is zero (e=ir) That MIGHT not mean anything unless those readings were made just after starting a cold engine. As I said earlier, I really don'r know how to interpret the sense readings for the wideband, but obviously what you called "ground" is not ground, but that is consistent with the diagram.

So, what do I believe all this means? I do not know.- Are you sure you have the correct wideband lambda sensors installed in the upstream positions? MAYBE your original sensor was bad but now the wrong sensor is installed. If the right sensors are in, why is the heater circuit calling for no heat? Is this code part of your stumbling, or just another unrelated condition? I would get a scanner that can indicate and chart the lambda readings and see what is going on with them. AND, the diagram shows three different grounds coming out of the ecu, (under the plastic cover near the right hood latch) which should connect to chassis right near there. BTW, I suspect that less now that you have read voltages that indicate current flow on the downstreams.

Good Luck- this kind of stuff can be a pain in the assand make you snappy to others!



.

 

All hail Sparkenzap!!! That is quite the thread. Wow! Taking your advice, I checked the upstream sensor part numbers to verify they are correct. Guess what? They sold me the wrong ones. They are not the Bosch wideband sensors, just universal 4 wire sensors. I get the CORRECT ones tomorrow morning. I'm hoping they'll take back the ones they sold me, but at this point, I'd be happy with a smooth running Jag. They sold me the wrong front rotors for my Excursion earlier this year, but they exchanged them with no hassles after I installed them and drove for a couple of weeks. Either way, thats Strike Two. What's the consensus about the wrong O2 sensors causing a Rich fuel condition, in turn causing the car to stumble during acceleration? Again Sparkenzap, Thank you. I hear NASA is hiring, but you may be overqualified.

 

Thanks for the vote of confidence, but just for the record I would not bet my money that you have fixed the stumble. However, you have made a step toward finding it. Good Luck.

 

All is well, almost. I put the new, CORRECT, O2 sensors in and the hesitation and stumble is GONE!!!! Except for an occasional rough idle and misfire while driving. It's very subtle, but after paying such close attention to the engine for the past three weeks, I could feel it. I checked the codes after the test drive and P0304 and P1316 showed up. I cleared them, ran it again and nothing. I'm going to give it a day or two and see if it reappears. I still have a coil coming in the mail tomorrow, so I'll hang on to it just in case. I'll try replacing the coil boot first, if I get another code. A new set of boots all around may be in order. Thanks again to everyone who contributed to this post. My apologies again to yeldogt for being ugly, there was no excuse for it.

 

Well, I bet my money on finding something wrong with A4 cylinder coil or sparkplug. It sounds like you are close to Jaguar Nirvana.

 

Well, after resolving the issue with the stumble (O2 Sensors), I have been dealing with an onslaught of DTCs. Mainly a P0174, system too lean B bank, and sporatic misfires on the A bank. The misfires are sometimes one cylinder, two cylinders, or all four cylinders. No real pattern, but always the #4 cylinder, and twice the #1 cylinder. I switched the #1 and #4 coils with the #5 and #6 coils, and still had misfires on the #1 and #4 cylinders, plus #2 and #3. Ruled out the coils. First on everyones list for the Lean condition is an air leak or MAF sensor. I couldn't find a leak, so I bought a new MAF sensor. Installed it this afternoon, drove 20 miles to work, no more lean condition or misfires. Finally!!

 

see and everytime i tell someone mass air flow sensor. They want to wish, pray, and clean them and wonder why the code still comes back.. Its a good try but if that doesnt work they need to be replaced.....like my momma always said, " you can clean and pig up real nice and put it in a suit. But at the end of the day its still a pig!" ::))

 

Back to the drawing board....the lean condition is still gone thanks to the new MAF, but I still have sporatic misfires. I decided to replace all the coil boots. They didn't fit as snug around the spark plugs as they should have so I figured, why not. Instead of buying Jag boots for $13 each plus shipping, I went to advance auto and bought Lincoln LS boots which came as pairs for $12. They were about 1" longer than the Jag boots, but after a little razor blade work, they fit perfectly. I ran it up the road a bit and no codes. We'll see if the codes come back in the next day or so.