Hi there. Maybe someone on here might have come across this problem before. I have a 420 dci premium 2005 t/u we use as a spare. It failed it’s mot on the air pressure in the emergency line was down slightly even though it builds up full pressure quickly. Also only one airbag in the rear axel inflates. No signs of any leaks. I’m guessing a valve issue but where do I start??
Many thanks for any help
Can you put on here exactly what the failure sheet says please 
Cheers
Steve
If it has individual bag control then its normal if uncoupled to have one bag uninflated.
Fuel tank loading will inflate one side but not the other, When a trailer is coupled this compensates and both bags inflate.
As for emergency line pressure being low,think somebody is feeding you bull.
If tank 1 and 2 are at full pressure how the hell cant you have trailer feed pressure?
Presume they told you this at the “test” station.If you have 9 bar at the red coupling
all it has to do is fill the trailer tanks.And if its filling the trailer suspension tank then you have to have enough brake tank pressure.
Thanks lads
It turned out the handbrake on one side was not holding enough on one side, the tester didn’t explain it properly to the driver so the emergency red line pressure was indeed ok. But regarding the air bag, it has independent side to to side control valves. One bag is definitely softer than the other even when you lift it. The tester said it’s not right even though I explained when it’s coupled up both bags are hard.
Can this be recalibrated or are all premiums like this? The bag that’s harder is on the fuel tank side by the way bking
There’s nothing you can do about the air bag being flat on one side when unladen.
There was a Tech Note about it years ago - If I can find it I’ll post a copy.
Steve
If you could find it that would be super I can print it off and show them
I don’t understand when they were looking at it, at test, without being hooked up?
Own Account Driver:
I don’t understand when they were looking at it, at test, without being hooked up?
What is not to understand? he presented a tractor for test without a trailer.Not rocket science?
Yep no hook up
It’s just the tractor unit that was being tested
trevm:
Yep no hook up
It’s just the tractor unit that was being tested
Take it to an ATF that doesn’t have a load simulator and hire a trailer.