Lexia codes help F408

[dumpvalve]

Hello all . ive just scanned my 2.2hdi x7 as I have.. fuel flap access not properly locked on the dash. ive got the fault code F408 and it says , Fault Fuel Filler Cap Not Detected.. iv checked that I have both magnets in the cap and it does , so the question is whats the next step? has anyone tried just buying a new OEM cap from Citroen, remember theirs no sensor as such on this model the magnets just complete a circuit, whats the difference between a P code and a F code, does the P code mean Permanent.

thanks
Andy

[RichardW]

I think P are just the OBD codes. There seems to be a raft of codes with other letter prefixes, but I don't know what they mean.

There is a reed switch in behind the fuel flap, so if the magnets are present, then this has either fallen off or is broken. If you look again in Lexia you might be able to see the status of the cap (which presumably will just show open?). If you can trace the wire back, then you may be able to bridge out the connector which will then let you see if it is the sensor or wiring the other way that is at fault.

The switch and wire is


Reference Description Quantity Price - VAT Price + VAT
00006534PF HARNESS 1 110.03 GBP 132.04 GBP

So you wouldn't want to replace it on a whim!!

[dumpvalve]

Hi do you mean the connector behind the fuel neck itself with 2 wires coming out of it , it sits at the back of the 3rd magnet in the fuel neck , you can only get to it from the rear wheel arch , ive had a quick look and cant find any wires cut or anything, I'm presuming I need to check resistance with a multi meter but unsure what readings I'm looking for, there is also a switch for the flap its self just to open the flap ive bought a brand new one from citroen £13 evidently just opens the flap with no electrical connectors

[Paul-R]

P codes are error codes according to EOBD specification so are generic to all vehicles. They're usually to do with faults that can cause emissions to the atmosphere and the like.

F codes are manufacturer specific and can only be diagnosed with manufacturers' code readers or high end code readers.

That's from memory - it might be the other way round!

[GiveMeABreak]

P code are 'Powertrain' codes - these follow the EOBD standards. For a brief explanation I have put together a quick table here:
EOBD Diagnostic Code Prefix Table

F408 is Fuel tank cap not detected. I will see what I can dig up.

[dumpvalve]

Marc thank you for all yr help with easydiognostics , I rang them up to confirm the correct Lexia with C revision and the guy was brilliant , and I got the discount , as my c5 is 2009 plate the software can go on a 64bit system , all has gone well and it reads my ECU spot on , I'm just thinking what root to go down next regarding the F408...

[GiveMeABreak]

Ok, no problem and glad you have it running. I'm sure you're aware now that although it will be fine on your car and later - it won't be able to be used on earlier vehicles circa 2007 or younger as that requires the encapsulated Lexia / PP2000 software what won't run under your 64 bit OS).

Back to the issue at hand....

I have been doing some digging, and although there would appear to be a warning light and message for the fuel filler cap open fault - I am not sure this was actually implemented in practice. As you can see from the diagram below, is is shown under warning T90, and if this was implemented, it would of course need an electrical connection to the actuator - which I have already looked at and cannot see anything listed apart from the connectors to the magnets on the actual cap and not the filler flap.

This is the same as the bulb out warnings - nobody has yet been able to confirm any warning shown on the diagram as actually being active when they've had a bulb failure. Perhaps it was included in the original design planning, but cost savings won over in the end!

'Icon representing an open fuel filler flap'

[dumpvalve]

All I can presume is,,, the wiring Harness from the switch is damaged in some way or the magnets in the cap are not strong enough other than that i don't see what else it points to

[bkod]

I've done some reading on international Citroen forums and most likely your fuel cap sensor is damaged. Magnets in your cap change the resistance of the sensor when cap is on. You could try and measure resistance of the sensor with and without the fuel cap on.
If you go to servicebox and look for the sensor by your vin, it sometimes tells you the nominal resistance of the harness so that might be a clue.

[dumpvalve]

Hi there is no sensor on the x7 models.. What about just buying a new cap OEM cap