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My truck won't raise. I get some air in the rears but nothing going to the front struts. I've been at this for a while now so I have some questions, any help is appreciated.

When I got the truck a month ago, the truck would raise to normal height but throw error C1A20 "pressure increase too slow", and I'd have to clear the code to get into other heights. Also, over a few days of not driving, it'd be on the bumpstops. I removed the fuse and measured the drop overnight, found all sides dropping an inch - inconclusive to a single leak. I replaced the front struts with Arnotts anyways since they were original to 2006 and after 120k miles, were long overdue. I drove on the replaced fronts for a few days and it was great, but still got the normal height only error. the Replacement rear Arnotts are coming this week as they are also original, and after feeling the difference to ride quality from doing the fronts, I know it'll be well worth it.

Then I got a rebuild kit for the original Hitachi pump, which is where I got some new problems. I probably should have left the pump alone and just done the dryer, since the pump was raising the truck at the time, but I thought I'd get better performance with a rebuild. :roll:

I'm getting C1131 "air supply" error code about 30 seconds to a minute after startup. I can clear the codes and the pump starts up again but then errors and stops after another 30 seconds. With my "carsoft" scanner, I can see the gallery pressure rise to just over 700kpa (100psi) but as soon as the error is thrown and the pump stops, the pressure quickly falls , returning to 87kpa faster than it took to pump it up to 700. This makes me believe there are two possible problems here, one the pump isn't making enough pressure and two the gallery isn't holding pressure.


  1. After the error is thrown and the pump stops, I can hear air hissing from the rear of the pump for maybe 10-15 seconds afterwards. Is this normal function of the "exhaust valve"? I thought it would be just one quick burst. I've not been able to find the source of the leak with soapy water, but access to the back of the pump is limited when it's installed and the tires are on.
  2. Where is the "gallery pressure" measured, before or after the non return valve (NRV)? If measured on the tank side of the NRV, then the pressure shouldn't drop so rapidly regardless of the pump possibly leaking? This would point to a problem with the NRV or a leak after the NRV. I've soapy water tested the valve block and the connections to the reservoir, no bubbles.
  3. Is the NRV part of the reservoir valve block, and if so would I have already cleaned it when I opened the valve block in two? If it's separate, is there a way to clean/rebuild it?
  4. Am I making any sense or have I completely lost my marbles? I'm almost broken down enough to get a replacement hitatchi style off ebay for $400CAD but it'd be a shame if my current pump isn't actually the problem or its just a bum o-ring causing all my problems.
Since the vehicle has stopped raising, I've disassembled the three valve blocks and cleaned them, where I found white powder in a lot of the o-rings, I believe from the old desiccant. When reassembling, I put a bit of silicone grease on the o-rings to help them seal. I also found a hair-line crack in the dryer cap, and have sealed it with superglue (and soapy water tested). No change to the error code.

I'm also wondering if the system makes pressure in the tank first (and throw a fault if it doesn't make enough pressure) before then sending the air to the bags. This would tell me if leaking rear air bags are causing the "air supply" code. I see the reservoir valve block has outs to the front and rear valve blocks, I just wonder if it tries to make a certain pressure first. The rear bags probably have a small leak but I don't want to wait a week for my new rears to arrive and find it's done nothing to solve the air supply issue.
 

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If your original struts were at 120K then they most likely had leaks. Compressors have to work over time to maintain the tank and keep up with leaks. This takes it's toll, compressors are a wear item. The error you are receiving is telling you bluntly that your compressor no longer has the ability to pump enough air to maintain the system.
 

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Discussion Starter #3
I understand that, and I'm spending the day pulling apart the pump and checking my rebuild job. I'm trying to figure out if a leaking air bag could through the "air supply" code on its own, or if the system is smart enough to isolate the pressure going in vs the pressure going out. Is there a different code for detecting leaks after the reservoir valve block?
 

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Discussion Starter #4
I pulled apart the pump and reassembled with an o-ring I hadnt changed. pressure when up to 890kpa but still throwing the error. I'm gonna start borrowing parts from my dads 07 range rover sport to see if I can find the culprit :)
 

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Airbags have no sensors thus can not "throw" a code. The system does indeed monitor tank pressure and how fast it reaches operating pressure. The C1A20 code you have received is due to the compressor not being able to fill the reservoir fast enough. I don't think I have read of a reservoir leaking on any model. If you don't have a leak then you have a weak compressor. Have you double checked your rebuild to make sure the seal on the piston has not slipped or become damaged? You say you pulled it apart and changed an ORing.
 

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It would take alot of neglect of the under carriage and some pretty serious rust to get reservoir to leak. Those tanks are very robust and thicker than required to contain the air pressure. I suppose if someone had a faulty drier on their compressor moisture could be introduced to the tank. It would rust a lot faster from the inside than from any surface rust on the outside. It's really no different than an air compressor in your garage. The tank has to be drained occasionally if you don't have a drier installed on the intake.
 

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Salt water probably contributed to my reservoir eventually developing a small hole as we did a LOT of beach runs down on the Gulf coast and even though we'd wash the vehicle on the underside afterwards...

, nonetheless, it would seem that northern climates with salt on the roads may contribute as well. Either way, if that's the issue, it's an easy fix...
 

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Discussion Starter #9
*update*
I borrowed the air pump off another range rover sport and tested it in my system, no errors and car raised up just fine after a few minutes of building up the pressure. So I know what I have to do now, I will venture the rabbit hole no further. New pump time. :cool:

I took a pressure reading off the other RRS before pulling his pump, and it was getting up to 1784kpa before the system shut the pump off. And the prolonged hissing from the pump after it shut off, a worry in my first post, was also present in the working pump. Just thought I'd throw this out there for future diagnosis.

When I put the working pump in my vehicle, it only got up to around 1500kpa before the system shut the pump off (no errors). This may be because I have leaking rear bags, or maybe my system is programmed to run lower pressure? His RRS is a 2007, mine's a 2006. I have new rear struts coming this week so hopefully :pray: that's all the leaks!

I'm probably going to go with this kit, as it's the cheapest all inclusive kit I've found, unless anyone has advise:
LR023964 Land Range Rover Sport LR3 LR4 Air Suspension Compressor Pump + COVERS
 

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Hey, 120K miles is a pretty dang good run for original EAS parts. They are wear items just like tyres and brakes.
 
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