Hi All, new member here in need of some help please.

I'm just back from the local test centre with a bit of paper that tells me my XJS has failed it's emissions fairly dramatically. The details are as follows :-

Model :- XJS 4.0 AJ16, UK model built late 1994 (actually a 1995 year spec)

• CO Idle % 5.950 (was 0.010 last year)
• HC Idle ppm 870 (was 33 last year)

It has around 80K miles on the clock but currently has very little use - less than 200 miles in the last year.
The car is running fine with no roughness or issues.

So I've plugged in my OBD2 scanner and it reports the following faults :-

• Error Code P1193 - O2 Sensor Heater Circuit Open - Inferred Fault.
• Error Code P0327 - Knock sensor (KS) 1, bank 1 – low input

Now I am very aware that the error codes are diagnostic and point in the direction of issues rather than telling you what to change.
So before I go off and change the O2 sensors what else should I be looking at ?
- The wiring harness and connectors to/from the O2 sensors
- MAF sensor clean

What Else ???

(I am assuming the Knock sensor fault may be due to the inclement weather today and will reset and test again when things dry out)

Thanks in advance
Neil

 

Knock sensors rarely fail, so even though the code points there, I wouldn't be so sure, just yet anyways.

First thing I'd do is replace the oxygen sensors. A failed, or failing sensor could cause the conditions you're seeing. Are these the original sensors? If they are, or you don't know the answer, then its time to change them. They are not designed to last forever.

Second thing I'd want to do is dump the fuel you have in the tank. I know that might not be possible, but I suspect you could have a really bad tank of gas.

It most probably is the Bank 1 oxygen sensor. If it was bad gas, or a MAF sensor, etc, you would see both banks coming up with a fault. Now don't be silly and just change the Bank 1 sensor....that second one is likely ready to go very soon as well. A bad oxygen sensor can trigger a knock sensor issue.

 

Neil,

As mentioned, forget the knock sensor code for now. The only time I had a strangely high CO figure on my AJ16 was when I had a failing lambda sensor.

For your own peace of mind, check the wiring connections on the sensor harness, and also the ecu connections and pins. But maybe it's time to invest in a couple of new lambda sensors.

I suspect that once you have the ecu getting correct readings then the knock sensor fault will disappear.

If you're going to syphon the fuel (as I did recently when recommissioning a friends AJ16) push a thin tube down the filler until you feel / hear it hit the tank bottom. It's really not a very far reach down. Pushing it further causes it to turn up back into the air space. Then syphon. You'll get quite a lot of it out. Then put some fresh (low / zero ethanol) and let it mix with the residual, before starting.

Good luck

Paul

 

The Downstream O2 sensors share an output for the heater from the ECU. What the code P1193 saying is that there is a high resistance on that circuit. That could be a sensor fault or a wiring fault or a dirty/corroded plug etc on either or both sensors. You will need to investigate to find the actual cause.

 

Thanks for all the thoughts
I don't know whether the lambda sensors are original but they are at least 22 years old so definitely up for replacement.
The car is a UK spec XJS-AJ16. It seems to only have two sensors, one in the downpipe from cylinders 1-3, the other in the downpipe from cylinders 4-6.

Does anyone know if this is correct ? or are there another two cunningly hidden further back ?

The two sensors I can see are pretty well corroded in place. I have soaked them in WD-40 in the hope they may free up.
Are there any other hints or techniques I should be using to get them out or is it just a matter of "brute force and ignorance" ?

I would guess the fuel in the tank is OK given that the vehicle is running smoothly, but I will syphon and refill just to be sure.

 

Neil,

Yes, UK cars have just 2 sensors. And YES, they can be tight! Try some heat on them.

See the other thread about o2 sensors for a link to www.gendan.co.uk and their titania sensor for the XJS. I've always found them good to deal with.

Cheers

Paul

 

Everyone goes straight for the complex - first ensure that you have no vacuum / intake air leaks, don't be so quick to go chasing computer information a heater not working is an issue but once hot the sensor should still have an output - you need a scope to diagnose - you may simply need to disconnect and reconnect with some electrical contact cleaner such as Servisol Super 10. The knock sensor only retards the ignition for lower grade fuels.

WD40 is not a penetrating fluid ....

Whilst there does seem to be a potential circuit issue I suspect it won't be the only one if the car has just sat around for most of the year (I'd have done 200 miles just blowing the dust off before a test never mind for the entire year) - the electrics in any car will degrade when standing unused, simply going around the car with contact cleaner separating and reconnecting connectors can resolve many issues.

 

Thanks to all for the input on this.
I'm just back from the test centre and the XJS has now passed its emissions test - Happy days.

To get to this point I spent a few days soaking the O2 sensors in WD-40. This freed them sufficiently to let me remove them with a 17mm spanner and a hammer.
New sensors we bought from SNG Barratt and installed.
Contact cleaner was used on all O2 sensor connections and on the MAF sensor.
I found the knock sensor, it was loose. I cleaned the connector and re-connected.
I filled up with a full tank of premium BP fuel.

The result was that all error codes are now clear and the emissions are sufficiently reduced to pass the test,

BUT

I still think there may be an issue. The CO reading was 0.28 (pass is 0.3) which indicates to me that things may still be running on the rich side.
What to I check/change next given that there are now no error codes ?

 

1. Replace Coolant Temp Sensor - sensor is cheap and easy to replace
2. Clean throttle body
3. Clean MAF Sensor

 

Neil,

You mentioned that last year you had a CO of only .01 (that's remarkable) and HC of 33. Mine was tested last week and had a CO of .1 but a HC of only 10. I was running late for the test and didn't get a chance to really warm it up hard before the test.

I'd be minded to give it a really good run (100miles+) to let the ecu bed down with the new sensor readings etc. The readings can be a bit variable depending on the temp of the engine and how settled is the fuel cycle. etc. Also see what mpg you're getting on a run before focusing too much on a single CO test reading. I did 300+ miles last weekend and got 27mpg with an Andy bracket & a K&N filter.

Drive the car, you'll enjoy it and the car will appreciate it!