Hi all. Just a technical query for those in the know.
I have an issue with my 450 dxi premium. It got a new apu valve fitted in dec as it kept exhausting the air and the brakes locked on.
This weekend I have a similar problem and I’m not sure if it’s the valve is at fault again.
Basically when uncoupled it builds up full pressure and you can drive all day long with no issues. Couple to any trailer and I can get about ten miles then the air pressure starts to drop and the warning lights come on. No sign or sound of any leaks. If I switch off the engine for a while and then start it she build up full pressure again and I can go another ten miles or so. This has me stumped. Could it be a compressor fault?
I think the APU is what renault refer to their fancypants air drier that operates on quite sophisticated electronics. It may be that some sensor info from somewhere else is causing it to open the exhaust if you’ve had a new one fitted and the same issue.
If only with trailer I would be looking at the trailer control valve also. It doesn’t sound like a compressor fault unless a compressor fault stuffed the last drier and has now stuffed the new one, carbon build up is sometimes a problem.
Can you hear it ■■■■■■■ any air from the drier exhaust when uncoupled?
Hopefully Neversweat will be along, who is a Renault tech, and the issue might be familiar to him.
Hi thanks
No I can’t hear any leaks from anything when it’s coupled or uncoupled
Take it you’ve checked the susies.
Compressor flap valves coked up.
Wabco garbage?
Yep the Susie’s are spot on ok
I ended up taking off the compressor and it was pretty coked up inside alright , yep it’s a wabco!
I put a new berkraft compressor on it so I’ll see how it is tomorrow with a trailer, fingers crossed!
I would change the dryer cartridge as well and fingers crossed you might get away with it.
To be honest it’s pretty ■■■■ poor it wasn’t picked up by whoever changed the drier as it’ll be more than likely the carbon build up stuffed it in the first place.
Most APM failures are due to carbon build up - If we fit a compressor we have to clean out the pipes from the compressor to the APM - Sometimes it end up blocking them though - The stuffs pretty potent as it takes the coating off the inside of the flex pipe so that has to be replaced afterwards no matter what. Always change the silencer on the bottom of the APM when changing its filter as this clogs as well causing back pressure. If you get a genuine filter you alsoget a yellow sieve filter that goes inside the APM . Your problem could be either the APM is jamming and its leaking all the time but you can’t hear it very well as its coming out of the silencer or the compressor valves are sticking. There is a pipe from the APM back to the compressor that feeds air at max pressure to let the compressor run light - disconnecting this pipe can stop this but then the compressor runs heavy all the time.
Steve.
neversweat1:
Always change the silencer on the bottom of the APM when changing its filter as this clogs as well causing back pressure.
Are there any issues with running without an APM silencer fitted (apart from the noise at blow-off)?
Harry Monk:
neversweat1:
Always change the silencer on the bottom of the APM when changing its filter as this clogs as well causing back pressure.Are there any issues with running without an APM silencer fitted (apart from the noise at blow-off)?
Just noisy Harry - Normally comes off if it’s blocked - Probably contravenes some EU directive regarding decibels with it missing though 
Steve
Gents. getting a trailer control fault and sometimes a danger wheel lock`warning on my 2006 Premium DXi.Have looked through old posts that suggest the trailer brake modulator could be the fault (no trailer is attached),where on my lorry would I find the trailer brake modulator ? As you can guess I have very little experience but many thanks in advance to anyone that can help or give me further clues .