i have had the same problem every one is telling you its the transponder but this is very rare the problem is usualy the coller around the steering lock its called an antenna its about 50 pound does it show immobiliser on the dash or transponder the coil in the coller is just not reading the key i have an fh12 and a 16 they have both suffered this problem no need to buy complete lock if that is the problem just the coller
Have you checked the relays, the power relays are K1 - K4 one of them is the “bodybuilder” relay you can swap that with the other 3 in turns.
Happens regular that the relays give in
Replace them + K5 every 2year (K5 is I-■■■■ relay)
Don’t search to far on diesel lines if it has been good so far, look in the electrics
You won’t get an error message on your screen, but he turns over without firing up.
If you lok inside the fuse box cover you find the relays on the top left hand corner is a group of 4
keith the thief:
i have had the same problem every one is telling you its the transponder but this is very rare the problem is usualy the coller around the steering lock its called an antenna its about 50 pound does it show immobiliser on the dash or transponder the coil in the coller is just not reading the key i have an fh12 and a 16 they have both suffered this problem no need to buy complete lock if that is the problem just the coller
caledoniandream:
Have you checked the relays, the power relays are K1 - K4 one of them is the “bodybuilder” relay you can swap that with the other 3 in turns.
Happens regular that the relays give in
Replace them + K5 every 2year (K5 is I-■■■■ relay)
Don’t search to far on diesel lines if it has been good so far, look in the electrics
You won’t get an error message on your screen, but he turns over without firing up.
If you lok inside the fuse box cover you find the relays on the top left hand corner is a group of 4
i would hope the OP has got it sorted by now, seeing as this thread is nearly 2 years old 
i have a volvo fh12 420, it did a load on wednesday no hassle,parked it up today,when back to it tonight and it wont start/? what could be wrong,
has diesel in it
good battery power
no leaks underneath it
turns over ok
its like its out of diesel,i mean that how it acts,but its not
there is an alarm on it, original volvo one, you push the lil rectangle thing that on the key into slot that has a red flashing light on it, you wait until it turns green, then u start truck, if you dont do this it wont start and turns over like it is now,except light does turn green, its ready to start,but still wont,
? anyone?
What year is your FH? Version 1 or Version 2?
try spare key sometimes transponder plays up .
check around deisel pump that there is no leaks because it sounds like its getting air in the system normal fault in cold weather over years seals can go therefor letting air in .
434mike:
What year is your FH? Version 1 or Version 2?
its version two i’d say its 1999, its not the early 1995 version,
version 2 yea,
what u think could be wrong
psv8:
try spare key sometimes transponder plays up .check around deisel pump that there is no leaks because it sounds like its getting air in the system normal fault in cold weather over years seals can go therefor letting air in .
guess i’ll have to get cab up, so you think the alarm thingy could be playing up, anyway to bypass?
argosy_610:
psv8:
try spare key sometimes transponder plays up .check around deisel pump that there is no leaks because it sounds like its getting air in the system normal fault in cold weather over years seals can go therefor letting air in .
guess i’ll have to get cab up, so you think the alarm thingy could be playing up, anyway to bypass?
just try the spare key as the chip inside the key plays up therfore would show up as working but not be doing its job .
imobliser will more than likly be on the pump but could be wrong .
i would try diffrent key failing that crack open one of the injectors nd turn the engine over a a few times while someone checks to see if any fuel is coming out , if so i would elimanate the imobliser .
A cure all for everything, check the stackpipe, either blocked with leaves or split… it is in the tank
psv8:
argosy_610:
psv8:
try spare key sometimes transponder plays up .check around deisel pump that there is no leaks because it sounds like its getting air in the system normal fault in cold weather over years seals can go therefor letting air in .
guess i’ll have to get cab up, so you think the alarm thingy could be playing up, anyway to bypass?
just try the spare key as the chip inside the key plays up therfore would show up as working but not be doing its job .
imobliser will more than likly be on the pump but could be wrong .
i would try diffrent key failing that crack open one of the injectors nd turn the engine over a a few times while someone checks to see if any fuel is coming out , if so i would elimanate the imobliser .
electronic injectors on them ! we had 1 that was an r-reg and it was like tha it turned out to be a fuse if ya take the center of the dash out behind te cup holder am sure it was something to do with the diagnostics fuse, make sure every fuse is ok
reply an let us know wa the problem was 
we had the same sort of thing with Scanias turned out to be a secondry filter in line that Scania had put in and hadnt advised wkshops they blocked up with the cold weather
On some FH’s, if the Oil pressure sender unit is faulty the engine won;t start as the engine management system needs to have oil pressure before letting fuel through.
could be the manual lift pump losing its pressure and your fuel is running back see if uv got any pressure on the primer its a common fault on them, pump should be about £25
The stop solenoid? Don’t know about truck engines, but certainly on a diesel car I’ve had it play up. It closes a valve in the fuel line to stop the fuel flow when you turn the engine off. They can stick, so they don’t open when you try and start again.
The solution was a light tap from a hammer on the solenoid to unstick it.
Like I said, that’s on a car though.
any joy ?
turn the isolater off and leave for 20 to 30 minutes. it resets the computer and when i have had similar problem its cured it.
argosy_610:
i have a volvo fh12 420, it did a load on wednesday no hassle,parked it up today,when back to it tonight and it wont start/? what could be wrong,
has diesel in it
good battery power
no leaks underneath it
turns over ok
its like its out of diesel,i mean that how it acts,but its not
there is an alarm on it, original volvo one, you push the lil rectangle thing that on the key into slot that has a red flashing light on it, you wait until it turns green, then u start truck, if you dont do this it wont start and turns over like it is now,except light does turn green, its ready to start,but still wont,
? anyone?
I hope its going now, my moneys on none return valve in the fuel pipe being your problem.
by the time you have gone for all the advice on here you could have stripped it down and put it back together.