Hello Chaps,
Well, this is annoying. I've been chasing the same pair of lean codes on my XJ Sport since I got her back on the road full time at the start of March. They are: P0171 and P0174 which tell me both banks are running lean. I've checked and cleaned the MAF sensor, the part and full load breathers, the snorkel, the rubber seal between the TB and the snorkel, checked the intake manifold is buttoned down tight and that the air hoses to the TB are intact too. I've cleaned and checked the TB too, but I still get this code.

Normally when it rears it's unwelcome head I get "Restricted Performance" for a few moments and the MIL/CEL light stays lit until I clear the code.
I've just driven the car around for three hours on a mixture of motorway, country, town and suburban roads where I've gone fast, slow and sat in slow moving traffic. I did this to see if there was a particular "trigger" for this event, but it seems as though there isn't. It came on whilst I was on the motorway and again (after I cleared it) later on whilst gently moving through traffic.

Seeing as this relates to both banks, I'm not thinking it's an 02 sensor, although it would be bizarre if two sensors have gone at exactly the same time. I could really do with solving this one as I'm supposed to be driving this car on a 1500 mile trip to and around Belgium and back home again in less than a month.

Any ideas?
S.

 

Maybe a long shot, but check the O2 sensor's heater relay. It's located in the engine bay (next to the ECM) and controls all four O2 heaters (AJ27 got four heated O2 sensor). See HERE http://www.jagrepair.com/images/Auto.../jagxj2002.pdf for the electrical guide of MY 2002 where you can find the exact relay location.

Having the O2 sensors not hot enough, they can cause the DTCs go haywire. And since the relay costs just a few bucks, it's worth a try.

 

Stu, apart from that what Alex wrote, there isn't much what both banks share.

Lean could be a vacuum leak somewhere. Have you searched for a leak somewhere? There aren't many areas it could leak from, luckily, but just check. The hose from the TB elbow to the brake servo can crack (mine was) resulting on a lean mix (I had a lean mix code). Or the take off for other vacuum connectors (not sure if your's has the same, as my AJ26 is more primitive).

Also, have you tried the throttle body? If the butterfly valve opens further than the sensor reads, it could also lead to a lean mix.

 

Thanks for the replies, I'll check those items tomorrow. I wouldn't normally bother the forum with something like this, but with it being so persistent I sought outside input. If it was something as simple as a relay I'd literally fling it over the roof of the house.

Daim, I searched and searched for a leak using the easy start puff method to try and find leaks. It's a bothersome thing this.

 

Yep, can be - but don't beat yourself up as you're doing the right kinds of things. Some more effort should work. Remember you can check if it's a leak by seeing if the LTFTs drop when you rev the engine.

 

Stu, did you check the actual functioning of the MAF sensor?
You might have cleaned it, but the do go off or out.
You will need to check it 'live', Jaguar values below in the attachment.
And as the MAF supplies both bank, its might be a suspect.

Besides, I had problems with the connector and wiring for a while, which let trim values spike all over the place.
I cleaned the connector, re-bent the clips, used some connectivity grease while install, but what did the final trick was to turn the connector on its wire a full 360 before connecting.
Seems the tension keeps things tight, and I left it like that ever since.

 

Recently I had a P0171/P0174 fault with my wife's 2001 XJ8 and looked for intake leaks (none).
I swapped a known-good used MAFS and the fault did not return.

You can read live data as others have suggested. You might try reading the data and using a flammable carb spray around suspected leak areas and watch the data readings.

A noticeable jump in readings or engine idle might indicate a source of 'false air' (induction leak).

Keep diagnosing.

bob

 

I am having a similar problem with my Vanden Pas, (I Know different car, but same problem), Did the cleaning of the MAF, checked the hose connections on the Purge Valve,
New O Ring seal on the lines coming off the valve covers. Still had the code come back after driving a bit like you in different areas and speed, got home, pulled in front of garage and the code/warning came on. Since I was going to replace the valve cover gaskets (need it) I changed the Purge Valve, fuel injectors (my son bought me some), and still getting the codes and all. What I did find out after a bit more reading, The coolant temp. sensor can also cause this problem, so now to check that, my check is to replace it, but the connector needs replaced as it was brittle and craked

 

It's using pretty much every sensor as here OnBoardDiagnostics.com - Engine Basics

 

If you decide to replace the temp. sensor just buy a new crossover pipe. It includes the sensor, and also gets brittle.

 

The suggestion is good, and the cross over pipe often overlooked.
Same material as the thermostat tower.

However, I think the engine should run rich if the coolant temperature sensor is out, at least if the engine is fully warmed.
Seems not the case for Stu.

 

Eric, I do agree. Just wanted to recommend changing the pipe instead of the sensor, and not a bad idea as a maintenance item.

 

I do agree that you agree that I agree on change the pipe.
Now it is up to Stu to agree

 

I agree too! As you can also get the same pipe as an aftermarket part too! .

 

Hi, sorry for not replying, yesterday was a busy day for me and I never got a chance to look at the car. I'm of for four days now, so hopefully can try and get this nailed down.

I'll try swapping the MAF sensors round as suggested, and see what that gives me. I'm also going to replace the relay to see if that helps, I've got about 50+ spare Jaguar relays from my previous XJ's I've checked for leaks all over the system, but nothing seems to be jumping out at me. I might replace the TB gasket just to rule that out, it's only a cheap part.

I recently changed the thermostat with an OEM one, the old one was faulty. I've yet to fit my alloy tower, but the plastic one is sound so I'll run with that a little longer. I've just not had the time or inclination to tackle the tower yet. The plastic crossover pipe was also ok, but I've got a spare one of those with a sensor attached so a "lets see" swap might be in order if nothing else works.

This is annoying, when I bought the car I drove it 110 miles home and there were no issues at all. This is something that has developed whilst she's been inactive during the renovation. I've not really touched the engine either during that time, the code first popped up during a nice sedate drive after passing the MOT test.

 

OK Just a little update on this:

I swapped the relay as advised first, as that was an easy option. I eventually got those silly screws out of the ECU box and swapped the relay, replacing the silly screws with conventional ones. I know the silly screws are for security, but as I got them out with a flat head screwdriver and light pressure they're not that good.

Anyway, it wasn't the relay as the light came back today

Returning home, and after lunch, I popped the bonnet and removed the MAF. I replaced it with the one from my old XJ which I gave a clean first. I also removed, cleaned and closely inspected the full load breather hose and it's connections, which were all fine. I left it at that as I'm trying to work through this methodically rather than blitzing it all at once.

So I need to do more test miles, which isn't a problem




Silly Screw vs Conventional Screw.

 

Well, hoping it works out, I give it a good chance.

But I don't understand is why you don't get some readings on your smart phone (of course supposing you have one).
In stead of the light, which is more of a on/off switch, you will be able to see immediately your engine readings, including the MAF functioning, and the fuel trim levels.

It is soooo much pro-active than waiting if a light or code returns.

 

Because I don't have the equipment to do that sort of thing. I've only got a very basic OBD reader, believe it or not, and it doesn't allow you to view trims etc. Now I'm starting a new job with better wages, I'll probably be able to invest in a better OBD reader.

However, it won't be phone based. If a Police Officer in the UK clocks you using a phone in any capacity whilst driving, you've had it.

 

I've got a little netbook with XP and JLR/IDIS. Does the job right. Software cost nothing and the netbook was an Ebay job for like EUR 30. Only thing you need is an adapter for the USB port. Mine is a Mongoose...

 

Ideally whatever I get, I'd like to be able to run it off my iPad as that'll be convenient for me with it's big screen and ability to be placed out of sight of the Polizei's prying eyes.

I took her for a 50 mile run this morning, and nothing has come up yet. She'll probably sit for the rest of the week, but I'm intending on having her out and about next weekend.