In other words, I have just gotten a return P0456, when I sort the problem, will this code automatically go away? I don't want to keep clearing codes if I don't have to. Thanks.

 

No if there is a problem the code will stay. If you fix the problem yes the error code will go away eventually. It will take a number of what's called "Drive Cycles". Just a fancy word for driving the car around and shutting it off and on! If you want after the repair you can clear all codes so you don't have to wait for the drive cycle stuff to complete.

I find clearing the codes regularly is a good habit as the system retains things forever and it's gets confusing to see all the "historic" codes when you really are just interested in what's currently wrong.

This happens with all codes not just the "P" codes.
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Thanks very much!

 

P codes generally stay around until the cause goes away and stays away, then P codes self-clear (well, stop putting on the MIL). Usually the cause needs to be gone for 4 warm ups (rather than drive cycles but don't get too fixated on the minutiae). Most causes only go away due to a fix!

The code stays recorded for ages (so a tech can see it in case an owner is late bringing a car in which has a problem that's intermittent, rattling cat, loose connector, or some such).

Eventually a code is completely erased on cars of the S-Type era - there are plans not to do this on newer cars but I can't recall if they are implemented.

 

Certain fault codes come and go on a semi-regular basis. Unless you are checking codes after every trip, you may never see them. How so? Based on the severity of the condition, many pending faults have to be seen on successive drive cycles before the driver is alerted. The idea is to limit false alarms, often caused by temporary conditions.

Even if the a fault changes from pending to a hard fault, the system is designed to automatically clear after certain criteria are satisfied. Typically, It's X number of drive cycles without a recurrence.

For example, a loose gas cap can cause a fault with the evaporative emissions system. Tighten the cap (correcting the fault), and the code will automatically clear as designed, although it may take a few drive cycles.

Got a misfire code caused by a bad coil? Fix the problem and the code will automatically clear. IIRC, this code clears right away, but don't quote me on that.

Tired catalytic converter, occasionally showing as efficiency below specs? This is a common one, more prevalent as a cat ages. If it keeps returning, you're probably looking at a new cat. But a single pending code once every other month or so? That's specifically why the system was designed to require more than a stray instance before alerting the driver. And the pending code will automatically clear on its own if not repeated.

 

Out of curiosity, I see advice about smearing grease on the gas cap before installing... so does that mean there is zero venting through the gas cap at all? Thanks.

 

Correct the gas cap is sealed these days. I would not put anything on that gasket. If it's not sealing just replace the entire gas cap.
If it's not tight you will get a EVAP code for a small leak and sometimes just tightening the gas cap will fix that.

Where I am at one of the emission tests is checking the gas cap seal.
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If you get a recurring code for a leak in the EVAP system, take a look at the sealing surface of the filler neck. It can get dented after years of repeated contact with the gas station nozzle. If damaged, the cap can’t seal and you’ll get a code.

 

Checked, but looks good. Am checking cap gasket for cracks.

 

Hi scrannel,

It's probably of less relevance in this case, but in general it is helpful to let us know the year, model and engine of your Jaguar, since this can make a difference in the diagnosis. To make this info appear in all of your posts, visit your User Control Panel and select Edit Your Signature and add the year, model, engine and mileage of your Jag and save your signature. This is very helpful to others who want to help you, and as you've already learned, the S-Type forum members are very knowledgeable and helpful!

A thorough smoke test of your EVAP system is one diagnostic tool for finding small leaks. But if your gas cap gasket seems to be sealing well and your filler neck seems undamaged and uncorroded, the next thing on my list to check would be your canister purge valve. They are known to fail. You can test it with a 9-volt battery to see if the solenoid valve operates and allows or prevents you from blowing through it.

Cheers,

Don

 

Thanks Don. My car is a 2008 4.2 NA. Will add that info and check out the purge valve.

 

Thanks Don for the smoke machine recommendation. This is one tool I don't have?
Do you have any suggestions? I have seen all kinds of things from a DIY machine on up. Just a lot of these out there.
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Hi clubairth1,

You can build your own functional smoke machine for about $20 - $30 USD - see YouTube videos. You can use a one-gallon paint can but I used a Harbor Freight paint gun bottle with latching lid because I had seen some like this for sale on eBay.

A smoke machine is useless if you can't seal the opening where you want to inject the smoke under pressure, so you need adapters to fit the various ports where you will want to inject smoke. These can sometimes cost more than a smoke machine. You can make some of your own adapters with just different sizes of rubber hose and one of the commercially-available taper fittings to fit onto the end of your smoke machine hose. I have assembled a collection of adapters to fit everything from standard EVAP Schrader valves to vacuum hoses, breather hoses, PCV valve ports, air intake pipes, throttle bodies, exhaust pipes, turbochargers, etc. along with blank-off plugs ranging from about 4 mm to 4 or 5 inches.

The "professional" smoke fluid is usually just mineral oil ("Baby Oil"), sometimes with a fluorescent additive so it will glow under ultraviolet light like A/C or cooling system leak detector.

"Professional" grade smoke machines start at around $500, and Snap On thinks you should pay more than $2,000. I probably have less than $300 in mine including the Harbor Freight paint gun, resistance wire, electrical connectors, EVAP and cone adapters, rubber hose, etc, but not including my turbo boost leak kit, which cost more than everything else combined. I have an air pressure gauge, flow gauge and manometer gauge that I'd like to mount onto a case into which I would mount the paint gun bottle so my machine would have the additional functionality of pressure adjustment and flow monitoring like the better commercial units have. I may never get around to it.

To learn how to use a smoke machine, a great start is to download and study the instruction manuals for commercial smoke machine models. Some are very helpful.

Cheers,

Don

 

Thanks again Don!

Now another favor? Any pictures of what you have built?
I do see Harbor Freight has released an Icon smoke machine but HF has really changed! It's $500!
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Sure! I'll try to work on that tonight.

Cheers,

Don

 

Here are most of the smoke testing items I've assembled over the past several years:




I built the smoke source in the bottle of a Harbor Freight paint spray gun. I patterened it closely after one I saw for sale on eBay. Beside the paint spray gun, the other parts were either things I had on hand or purchased from Amazon, eBay or McMaster-Carr. The smoke source uses a section of nichrome resistance wire wrapped around a length of Tiki torch wick submerged in mineral oil. Regular mineral oil/baby oil works just fine, though its smell is not pleasant, so it must be used with good ventilation. Commercial formulas vary but may include glycerine and/or glycol and a fluorescent additive to glow under ultraviolet light. You can add a little A/C system leak detector UV dye oil if needed. The hose that goes down the side of the smoke source feeds compressed air into the bottle to force the smoke upward and out. The pressure regulator on the bottle now is limited to 1 psi for safely testing EVAP systems:




I've collected various cone fittings for connecting to different size ports, air intake pipes, throttle bodies, exhaust pipes, fuel filler necks, etc.. At the center is an inflatable bladder that can seal inside tubes of various diameters. At the bottom is a short hose with a fitting for EVAP system Schrader valves and the red-handled tool is a Schrader valve core remover (the fitting does not depress the Schrader valve stem, so the core must be removed):




The smaller tapered cone fittings connect to various diameters of vacuum and breather hoses or to the short hoses on larger adapters. One of the tips is just a beach ball inflator tip and another is off of a helium balloon inflator. The wye and the hose with duct tape on the end are things I cobbled together for particular jobs. The 20 psi air pressure regulator at upper left can be used in place of the 1 psi regulator when testing air intakes, exhausts, etc.




This little tire inflation compressor plugs into the cigarette lighter so I can use the smoke machine on remote jobs away from shop compressed air:




The stack of yellow blanking plugs at lower left and the smaller rubber plugs and caps in the Sterlite container at upper right are useful for sealing hoses and ports that would otherwise prevent air/smoke pressure from building up in the system under test.




This is my most expensive investment, the Lisle 69910 turbocharger adapter kit for pressure- and smoke-testing turbo boost leak issues. It comes with its own adjustable pressure regulator:




Several years ago when I began shopping for a smoke machine and decided to build my own, affordable "entry level" options were limited. But today there are some very interesting affordable options and I would probably just start with something like one of these instead of building my own and having to source every adapter just to get started. For the occasional user, these machines will probably work just as well as or better than the one I built. If they had been available when I started my journey, I would probably have given something like these a try:





Cheers,

Don

 

Wow Don what a setup!
It will take a while to absorb all this and thanks for the cheap smoke machine pointers!
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Coming back to this: so if I use a 9 v battery to check my purge valve, how would it behave if not working? I presume if it does nothing, that's not good news, but if it opens how can one tell if it might be opening too soon in service? Thanks

 

To test the valve, you can blow into it with the solenoid unpowered and powered (briefly). In one state you should be able to blow through the valve, and in the other state the valve should be fully closed. If you don't fancy using your mouth and lungs, a hand-operated vacuum pump can be used.

The purge valve is operated via pulse width modulation, but it should respond to the 9 volt battery. If it operates very weakly on 9 volts, you can try briefly connecting to your 12 volt car battery. The solenoid should operate quickly and positively and the closed state should be completely closed.

I can't think of a scenario in which the purge valve would "open too soon," because it should only open when grounded by the ECM. But a common failure mode is for the valve to be stuck partially open, which allows unmetered air into the engine intake.

Cheers,

Don

 

Thanks Don -- head under hood!