need help with c5 lexia diagnostics

[Mandrake]

Fault codes read from the gearbox before driving or resetting fault codes:

(continued)

[Mandrake]

The next fault codes are those that were recorded after fault codes were reset and a very slow careful drive 50 metres down the road and back was performed: (During which the clutches stopped working a couple of times and we had to turn the engine off a few minutes to be able to move again)

[Mandrake]

Finally this is a snapshot of live sensor data taken crawling along the road around 10-15mph. (I think it was just changing from 1st to 2nd as the snapshot was taken) The snapshot was taken just before the pressure dropped below 1 bar, at which point the clutches opened and the car rolled to a stop.

As far as I could tell the clutches and gear change were working normally when the oil pressure was normal, there were no unusual noises, and when the pressure dropped below about 1 bar they simply failed to engage, acting more or less as if the gearbox was in neutral.

[CitroJim]

Ahh right, sorry for not fully reading the thread properly Simon

Now, that does kind of indicate a blocked filter in that it recovers after a time. The few minutes would give time for the pump body to fill again and get enough to pump for a little while.

Tell me, as the pressure falls could you hear a change in, or any form of noise from the gearbox? Normally if the pump is running dry you can hear a change of pitch or even a new noise as the pump runs dry...

[Mandrake]

To be honest I didn't think to get out of the car and lift the bonnet to listen for noises, being a diesel the noise from the engine was rather prominent and would have probably drowned out any smaller noises anyway. Sitting in the car with the door open and the engine idling I didn't notice any change in noise as the pressure dropped - all I could hear was the engine. At no time did I hear any noises unusual or otherwise from the gearbox.

[CitroJim]

Understood Simon, it is hard to hear what's going on when you have a diesel clattering away - even an HDi...

What's the next planned step? I think I'd be inclined to get a replacement 'box from a scrapper as I'm not sure if anyone has delved as deeply into an AL4 as has been done with an HP20...

Shame it's not an HP20 really as I could offer far and away more advice... Plus I have all the manuals...

[homer jw]

just a quick note to thank simon aka mandrake for his help it was much appreciated now we know codes or possible fault does anyone know what best to do next any info greatly appreciated and thanks in advance i have mechanic ready to help if he can be advised as he doesnt have any experience with this autobox

[homer jw]

any ideas what to do for sure

[homer jw]

anything

[Mandrake]

Hi John,

No problem, it was good to meet you, its a shame the problem wasn't something a bit less serious, like the oil wear counter just needing a reset.

If I read Jim's comments properly it appears the problem whilst in principle may not be major (it might just be a blocked oil filter feeding the oil pump) the problem is going to be quite major to fix in practice - the oil filter on the gearbox won't be accessible in place, at minimum its going to be a gearbox out of the car job with at least a partial strip down of the gearbox to even get at the oil filter as its down inside the bowels of the gearbox...

It's not the sort of job that a mechanic not familiar with auto gearbox rebuilding is likely to be able to tackle, certainly not without a full AL4 service manual on hand. (The PDF I sent you is a dealer training manual not a full rebuild/service manual, which I don't have)

Even assuming all that it might turn out not to be a blocked filter. There is an electro-valve that controls/modulates the oil pressure under command from the ECU which might be misbehaving, or there could be some other hydraulic fault causing a loss of pressure, or the pump could be faulty. Until its stripped down there is no way to know.

In short taking the box out and stripping it down could be a big crap shoot unless a proper rebuild is done by someone familiar with auto gearboxes, which may not be economic.

Jim's suggestion was that you might be better off checking nearby scrapyards to see if any have a gearbox from a similar model of C5, you might be able to find one well below the cost of repairing the existing one and as long as they're willing to refund you if it turns out not to be in good working order then its probably worth a shot - swapping the box over is far easier than doing a strip down job on the existing one.

Sorry the news isn't a bit better, and good luck in getting the car sorted out.

[DickieG]

If you do decide to get a box from a scrapper choose one that comes from a crashed car on the assumption that it must have been working to some extent right up until the point of impact (provided of course that it wasn't a side impact onto one of the front wheels )

[CitroJim]

In short taking the box out and stripping it down could be a big crap shoot unless a proper rebuild is done by someone familiar with auto gearboxes, which may not be economic.

Simon, amongst all your other wise words I quite agree.

If you do decide to get a box from a scrapper choose one that comes from a crashed car on the assumption that it must have been working to some extent right up until the point of impact

That's good advice Richard and applies to may mechanical/electrical things taken from scrappers.