D5 (D5244T to 2005) ECM 6805 low pressure from vac pump

[Newbie Tony]

Hi everyone

My 2003 XC90 D5 has thrown the fault code ECM 6805 a few times over the last few months. I've replaced the front engine pad (rear was and still is ok), and an elbow out of the VNT governor which had perished and normal service had resumed. Just for info I have today checked the control valve, engine pads and hoses, all pipework between the vacuum pump and control valve and VNT governor including the T pieces with a vacuum pump and gauge and all of that is holding pressure with my vacuum test pump.
I've connected the gauge directly to the outlet nipple on the vacuum pump that feeds the turbo side, and I'm only getting a reading of 15inhg. I believe the figure should be around 28. I've noticed that having connected my gauge, I go in and start the car and get out and walk back round and I can still see the gauge rising slowly up to 15inhg.

I'm thinking I have a problem with the vacuum pump itself but am not sure what exactly. I've read of two problems: leaking oil seals and perished o rings on the brake servo side. I have the quick connector on the bigger hose to the brake servo and it appears ok as do the hoses on the brake servo side of the pump. I'm stumped so any help would be greatly appreciated.
Cheers

[Clan]

Originally Posted by Newbie Tony

Hi everyone

My 2003 XC90 D5 has thrown the fault code ECM 6805 a few times over the last few months. I've replaced the front engine pad (rear was and still is ok), and an elbow out of the VNT governor which had perished and normal service had resumed. Just for info I have today checked the control valve, engine pads and hoses, all pipework between the vacuum pump and control valve and VNT governor including the T pieces with a vacuum pump and gauge and all of that is holding pressure with my vacuum test pump.
I've connected the gauge directly to the outlet nipple on the vacuum pump that feeds the turbo side, and I'm only getting a reading of 15inhg. I believe the figure should be around 28. I've noticed that having connected my gauge, I go in and start the car and get out and walk back round and I can still see the gauge rising slowly up to 15inhg.

I'm thinking I have a problem with the vacuum pump itself but am not sure what exactly. I've read of two problems: leaking oil seals and perished o rings on the brake servo side. I have the quick connector on the bigger hose to the brake servo and it appears ok as do the hoses on the brake servo side of the pump. I'm stumped so any help would be greatly appreciated.
Cheers

Have you actually tested the pump itself with nothing connected to it ?? ie , just the vacum gauge connected to the big vacuum port on the pump . Yes should be close to 28 in/hg

[Newbie Tony]

Thanks Clan. No I haven't yet. I'll do that after work today. Funnily enough, my engineer mate last night suggested disconnecting the vacuum hose at the brake servo end to check there's no leak in that pipe run. Your suggestion isolates the pump. If the oil seals are leaking in the pump would that cause vacuum loss? I'm trying to understand if it might? I guess if oil is getting out, air can get in?

[Clan]

Originally Posted by Newbie Tony

Thanks Clan. No I haven't yet. I'll do that after work today. Funnily enough, my engineer mate last night suggested disconnecting the vacuum hose at the brake servo end to check there's no leak in that pipe run. Your suggestion isolates the pump. If the oil seals are leaking in the pump would that cause vacuum loss? I'm trying to understand if it might? I guess if oil is getting out, air can get in?

I have yet to come across a pump with an internal leak .. you need to test it first if it cant generate and hold 28 in/hg or so you will need a new pump .

[Newbie Tony]

Ah that's a very useful piece of information! Thanks..... I will post an update later

[Newbie Tony]

So ...... I've just removed the vacuum hose to the brake servo and blocked up that port. I'm now getting and holding 29 in/HG from the nipple that feeds the turbo control circuit. It seems I have a leak on the brake vacuum side.

[Clan]

Originally Posted by Newbie Tony

So ...... I've just removed the vacuum hose to the brake servo and blocked up that port. I'm now getting and holding 29 in/HG from the nipple that feeds the turbo control circuit. It seems I have a leak on the brake vacuum side.

so it's leaking away through the brake servo ? do the brakes feel hard?

[Newbie Tony]

Interesting you ask that..... I don't drive it daily but recently I did think I was having to press the brakes a bit harder. I've just removed the last hose connection from the servo end and taped it up and I'm still getting 29in/hg from the pump. That would point to the brake servo wouldn't it? The plastic connection at the servo end is holding pressure and I was wondering if the rubber grommet might be suspect but I've just dropped it into the engine bay

[Newbie Tony]

I've just remembered that watching a couple of videos on vacuum pump replacement that when the connector is removed from the back of the servo, there's quite a "pop" due to the vacuum. When I pulled my connector off there was only the sound of a small air leak. This would confirm a problem with the servo unit I think?

[Clan]

Originally Posted by Newbie Tony

I've just remembered that watching a couple of videos on vacuum pump replacement that when the connector is removed from the back of the servo, there's quite a "pop" due to the vacuum. When I pulled my connector off there was only the sound of a small air leak. This would confirm a problem with the servo unit I think?

yes an internal air leak in the servo , can you hear any hissing if you gently press the pedal ? A rare problem which can happen .