Greetings All

Not posted for a while as nothing going on with my 2002 4.0 V8 S Type , well nothing out of the ordinary anyway.......until today.......
Had to do some work over the last 12 months, just MOT advisories.
Rear suspension bushes (upper & lower) both sides, new rear shocks, new front lower suspension bushes, couple of brake pipes.
Not bad really for a 20 year old car.

However, after doing the front bushes today, I thought I'd check my downstream O2 sensors as I have been getting a code pop up occasionally.
I had changed the sensors 18 months ago due to this code popping up before.
So, I checked the O2 sensor itself, heater side is fine, the ohms readings are good on both.
Checked the voltage readings.......nothing.
I then checked the readings at the plug on the harness where the sensor plugs in to, and no power supply at all.
I should be getting between 0.1 and 0.9 volts at the main plug, but nothing either side.
Thinking it might be just dirt or corrosion I gave the pins a scrape and clean as best I could but still no difference, no power.
So I've just scoured the electrical diagrams on JTIS and it appears that the wires go straight back to the PCM.
But I'm thinking that there may be a relay in the system somewhere as well, that I either can't see on the diagram or I'm reading something wrong.
Before I go and strip out the multiplug socket under the front and replace all the pins, could anyone enlighten me please?
I'd rather replace a relay than start replacing sockets and pins.

As an FYI, the emissions test comes back as near perfect as it could ever be, so that rules out cat failure in regards to the fault codes P420/P430

 

Do you have associated code(s) all the time for those sensor(s)?

If not, you're not checking properly. You'd definitely always have codes.

 

I'm not sure I follow your line of troubleshooting. Unlike most other sensors, there is no power supply from the vehicle to the O2 sensors. Think of an O2 sensor as a self-contained little voltage generator. The internal heaters are a separate circuit and yes, they receive power from the vehicle. But the output from the sensor itself? The power originates from the sensor and varies with the O2 content of the exhaust, and the computer reads this voltage.

How often are you getting the P0420 or P0430 codes? They usually indicate a failing cat, but it's not uncommon to get an intermittent code now and then. If you get either of these codes, don't rush out to replace the downstream O2 sensors or the cats just yet. These codes are triggered by comparing how dirty the exhaust is upstream and downstream of each cat. The upstream sensors rapidly switch lean and rich during normal operation, and fueling is tweaked to match. If a cat is working properly, the downstream sensor will show cleaner exhaust with very little oscillation. If a cat fails, the downstream sensor will rapidly switch lean and rich, just like the upstream sensor normally does. When the switching rate for the downstream sensor approaches that of the upstream sensor, this is interpreted as a failing cat and the code is triggered.

Bore you to tears yet? I mention all this because unfortunately the common response to P0420/P0430 is to replace the downstream sensors. However, the switching rate for a sensor slows down with age. A new downstream sensor will switch faster than the old one, and thus is even more likely to trigger a code. If you want to gamble, try replacing the upstream sensors but keep the old downstream sensors. This increases the desired difference in switching rate between the two sensors, and is less likely to trigger a code. Is this a guaranteed fix? Not at all, but I'd try it before replacing a suspect cat. Your mileage may vary...

 

What he said!

i’ve been fighting the P0420 and P0430 code for quite a while now and I actually had used the monitoring software from SDD last night to look at my fuel trims and O2 outputs. Below is what you’ll see when your cats aren’t doing what they supposed to do. By the way, the catalytic converter‘s on this car are aftermarket made by DEC or pacemaker and I put in all four new O2 sensors when I installed the cats.

 

One important point to mention: '03+ models use wide-band O2 sensors. Earlier models use narrow band sensors. A narrow band sensor can only say if the exhaust is rich or lean, but not by how much. A wide band sensor covers a (wait for it...) wider band and can indicate how rich or lean the exhaust is. Troubleshooting is similar, but a wide band sensor can provide much tighter control and won't cycle as much.

Not to get too far on a tangent, but are these new cats stock configuration or performance? If the latter, they may not be capable or achieving the same level of "cleaning" as stock, and thus the codes. Or even if they were okay when first installed, they may not have enough reserve capacity compared to stock and so would tend to trigger a code with age.

Another option: Have you considered O2 sensor extenders? They reposition the sensor tip out of the direct exhaust stream, and trick them into responding more slowly, which mimics what the computer wants to see. Not a true fix, but they do work.

 

yes you are correct about the earlier O2 sensors I didn’t catch that it was it earlier model but I’m gonna make my own posts to try not to model up this guys post but just for your FYI my cats were supposed to be compliant replacement cats, and not performance
And I had these codes from the gecko, but I was chasing some small, vacuum leaks that I have fixed, so I wasn’t sure of what was causing the code. In fact, I’m still not sure.

 

How's that Auto-Correct working out for ya?:

 

that damn gecko. never an understand a word I said. Voice to text can’t understand my mumbling.

 

"sorry mate, forgot about the codes
P0420 & P0430

 

[QUOTE=kr98664;2615609] Think of an O2 sensor as a self-contained little voltage generator.


Thanks Karl, that makes more sense. I'll run a different test then.
About these spacing collars.......Approximately how much do they extend the sensor out by?
I can easily knock some up on the lathe

 

[QUOTE=stevep10;2615809]Various lengths are available. A common size has an offset about 1". This moves the end of the sensor out of the direct exhaust path, and into a little pocket on the side of the pipe.

I tried to find some examples to show you, but they are mostly absent now from eBay and Amazon. There must have been a big crackdown from our beloved government, as previously they were widely available. Of course, these aren't exactly considered "legal". On the flip side, I know some manufacturers installed them by service bulletin to fix overly sensitive triggering of the codes.

Search for "oxygen sensor extender" or similar to see some examples. If clearance is an issue, 90 degree versions are available.

Be forewarned if your car requires emissions testing, and the procedure includes a visual inspection under the car, it will not pass.

 

[QUOTE=kr98664;2616027]I have tried using those extenders in the past when I put headers on my challenger, but I didn’t have much success and they threw code still because they interfered with the timing of a test where it would measure the reaction time of the O2 sensors when the PCM sent, they purposefully rich, make sure and then timed how long it took to see it change at the O2 sensors. I can’t remember which code it’s associated with, but I would fail that timing test because the headers with the extender delayed the sensing of that change in mixture outside the limit for the test. But for the 0430 and 0420 code the test is looking for the ratio of the lambda between the first O2 sensor and the second and I’m not sure there’s a timing parameter involved there.

I probably still have those extenders someplace so I might try them on my car to see what it does because I’m still getting that 0430 and 0420 codes

 

[QUOTE=Aarcuda;2616028]I don't think the early models had this self-test feature. For several years, I used an extender to milk the last bit of life from a marginal cat on my '02. No codes at all.

 

OK, so after taking the jag for the MOT, the tester found a couple of places that needed welding up. 4" section floor to sill passenger side and a smaller piece on the rear driver side rear.
Started on the driver side first, no problems there, cleaned up and plated well.
Over to the passenger side............................started knocking out the bad bit, and it ran like a good 'un. All the lip section rotted away as well.
By the time it got back to good metal I was staring at a 24" long plate needed to repair it.
Now obviously I would need to stitch it back to the outer sill as well, so the sill cover had to come off so I didn't melt it with the welder.
Then it got really horrible...............
The outer sill skin had gone through as well behind the cover. By the time I finished cutting the rot out of that, I was looking at a 54" plate to repair it, and I couldn't get a new sill skin from the motor factors either....................
So I just got stuck in and repaired everything.
Several hours of cutting and shutting and sealing and undersealing, it was MOT worthy again. And passed the test, thankfully.
But it made me make a decision to let it go. Now that I've had to plate it to this extent, over the coming few years I guess that I am going to start to chase rot in other places.
I've had the car for 5 years now, and it's lovely to drive, comfortable, plenty of room, power on command, and I really wasn't looking to change it, no need to until now.
So I bought another JAG.
A gold 2008 XF 2.7 diesel with only 49000 miles on it, and service history up to 45000 miles
It has a running issue which I'll deal with in time, but for £2000 I think it'll suit, and that's a different thread starter.
I'll continue to use the S-Type until the "new" one is sorted, but it's bye bye this room and hello XF room on this forum

Thanks to everyone who has chipped in over time for all your help, very much appreciated

 

I suppose it's 6 years younger so if it last 6 years and then goes the same way, very cheap motoring.

Be wary about the 2.7D - check the oil OFTEN for diesel.

 

Thanks JagV8
This 2.7 has a knock which I knew about. Had a look this morning and I can see that number 4 injector is leaking, or at least it is wet around the bottom of it. The dealer supplied me with another set of injectors that he bought but never got round to fitting so I'll get those in shortly and see what occurs. I've read the tales of bottom end blowing on these so the first thing I did was check the oil level and smell it for diesel contamination. It's right up on the max mark and I'm sure I can smell diesel in it, but I plan to do an oil and filters change before i do anything else. I've started a new thread in the XF section on the forum, I'll continue to update that

 

If anyone wants to follow the new thread, here is the link

https://www.jaguarforums.com/forum/x...diesel-267981/