Hi all,

I'm a new member here, having found you via google.

I believe my car needs an upstream O2 sensor on bank one due to code P1646. Can anyone confirm that's correct for a car first registered 2/2000? I believe the codes changed six months or so after that.
I'm also getting a P1121 code which seems to be fuel system related, I think it'll be caused by the P1646 code & the reason the car drops into engine failsafe mode at times.

Also do you the part number as I can't make sense of the chassis numbers on parts websites, they don't seem to match mine. I've had that issue before when ordering bits but the supplier sorted it without explaining how.

Thanks in advance.

 

for XJR O2 sensor fault code changed to secondary fuel pump fault code. I cant remember wich way it went now
Just find O2 sensor plugs right behind throttle body, you can trace the wires from sensor to plug with your eyes, disconnect both plugs and swap them, connect A bank sensor to B bank plug and vice versa. see if code change to P1647, if so then its O2 sensor fault, if not- then its your secondary fuel pump.

 

Cheers.

I'm pretty sure it's not the pump as that was replaced early this year, but your test proves it one way or the other.

 

Do you know whether your engine is AJ26 or AJ27? AJ26 has 2 wires to each ignition coil and AJ27 has 4 wires.

If it is AJ26, then the codes mean:


If AJ27, the codes mean:

 

Off the top of my head I don't know how many wires to the coils, I'll have to check this evening. From reading the ECU actions in response to the codes, I'd assume a AJ27. The actions for the P1121 code match the sequence of issues I get, 'No DSC, No Tracs, No ABS' and an unresponsive throttle with the engine running about 1,200rpm.

Do you know how to test the/reset the TPS as it appears that's probably faulty too, that remedy section suggests there is an adjustment that can be done.

I've just found the codes in a workshop manual I downloaded, wish I'd remembered I had that before!

Thanks for your help so far.

 

Sice the TB gets unresponsive to the accelerator pedal, it is probably AJ27. The simplest thing to try first is to unplug all connectors to the TB, inspect and clean the pins if there are any signs of corrosion. Sometimes, just unplugging and plugging the connectors back in a few times will clear any poor contact between the pins. Also check whether any of the connectors has gold plated pins in one half and zinc plated in the other. There was a Jaguar service bulletin about a particular connector (I cannot remember which one, MAF sensor or TB) which, from the factory, had a combination of zinc and gold plating which caused issues (poor contact). The service bulletin advised to replace the pins in one side of the connector to make their plating equal to that in the other side of the connector.

If this does not help, you may have to replace the TPS. I am not familiar with the AJ27 TB but, if the TPS on it looks like the one on the picture below, that is the only type that you can buy separately (and only China made).

 

For easier reference, I attach a drawing showing the TB and the two Position Sensors, Pedal and Throttle. I am not sure if the pedal position sensor can be replaced separately but, in any case, it is not available as new (not even from China). You may be able to find a used or rebuilt ($$$) one.

 

Thank you, I've been reading the workshop manual I'd forgot I had since getting home from work. So I know how to test it now.

Seeing what you say about sensor availability explains why throttle bodies for these seem to crop up regularly on parts searches, as if it's the pedal sensor it'd need the whole thing replacing.

I can confirm it's a AJ27, I've just checked the pics from when I did the secondary tensioners at the beginning of this year. That's quicker than taking bits off the car too look. There are indeed four wires to the coil packs.

The manual talks about testing the connectivity back to the ECU on plug EM11 (from memory) I've yet to find the ECU location in the manual, do you happen to know it?

 

Update as I've had a fiddle.

Previously both codes were appearing instantly when cleared just with the car idling. I've taken both sensor plugs off the throttle body, sprayed them with contact cleaner & reattached them several times. That might have solved the biggest issue of it dropping into failsafe mode as the P1121 code hasn't come back after several scans, even a bit of throttle use. I'll recheck after driving to work tomorrow to confirm that one.

I should have cleaned the plug for the O2 sensor too, but never thought of it till I'd put the intake pipe etc back on. I'll do that tomorrow as I had a rather early start today & need to eat more than fix the car. Looking at the ODBII readings, the fuel trim for Bank 1 is almost 9% where as Bank 2 is 0%. That makes sense to me as it's working of false readings or just in a 'failsafe' go a bit rich to protect the engine mode. At least looking at the job, it's the easiest O2 sensor to get to if it does need replacing.

 

Looks like you are progressing well. Don't bother with the links to the ECU for the time being as checking them may not be necessary. One thing about spraying contact cleaner - it cools the things quite a lot and causes instant moisture condensation which is trapped inside the connector if you plug it in immediately. I suggest you unplug the connectors you have sprayed and leave them open for a few hours to dry. In Malaysian humid climate, the condensation after spraying contact cleaner is such that you actually see tiny water droplets, I either leave the connectors open for some time or dry them with a hot air gun before reconnecting.

 

Interesting, I've not heard that before. It does make sense though, so thanks.

 

Well the TPS seems to have behaved today, so hopefully it was just a dirty connection.

I've ordered an O2 sensor, chances are it'll be gone. I've only ever known one show a fault that wasn't the sensor (the wiring had frayed) and I know the wiring to this is ok. It also means it'll be here for the weekend so I've got time to change it before the MOT is due.

 

Just recently replaced driver side upstream sensor. ECU doesn't show the code everytime even the sensor is broken. I could drive easily day or week in a row without any issues. Except slight erratic throttle response just above idle. That area was the most sensitive for the error code to show up. Sensor heater element was broken all the time.

 

I get codes all the time so I'm pretty sure it's broke. I'm surprised it doesn't light a warning on the dash tbh, but it seems it doesn't. I wouldn't have known if I hadn't checked the codes for the throttle issue.

 

Well that didn't work, it dropped into failsafe mode four times in nine miles this morning.

Bugger.

 

I have found a UK supplier of the TPS sensor though https://www.xk8-parts.com/2016/03/th...ve-as-a-spare/

 

That sensor looks very much like the China made ones available on Ebay (see the pic I posted earlier). Anyway, the new ones are only made in China.

Ebay, China seller: https://www.ebay.com/itm/New-Throttl...gAAOSwyExdWPYZ

Ebay, UK seller: https://www.ebay.co.uk/itm/Jaguar-XJ...AAAOSwkpxdUx6D

I think they are all selling exactly the same product but at vastly different prices. The only disadvantage buying from a China seller is the shipping time which can be more than a month.

 

As aj27 based engine, it has more accurate 4 wire wideband sensor as upstream sensors. These wideband sensors works completely different compared to the 4 wire narrowband what are used in downstream. And I guess that ecu doesn't actually measure heater current by any means. So if heater is broken and lambda doesn't give any signal in certain time -> bang a code from either sensor signal or more likely heater element.

 

I've ordered one from a UK seller for £40, it should be here the middle of next week to make my car mobile again.

Unfortunately I'd planned this weekend to scrape some surface rust, treat, paint & reunderseal it on the floors. I started to do that & found it's much worse than it looked so the only place my car will do is the garage to get welded before I can actually use it as the MOT runs out next weekend.

Good job we love these cars eh?

 

The new sensor arrived today, I plan to fit it tomorrow evening. I'll let you all know if it works.