Low Pressure AHC Pump Troubleshooting Help Requested (1 Viewer)

[AJLaz]

Greetings fellow enthusiasts,

Things have begun to go south on my '10 LX with ~95k Miles. A few weeks back I flushed my AHC with 0 initial problems, I followed the guides posted here including using the Metal can AHC Oil and I bled multiple times until the fluid from bleeders was perfectly clean. I cycled low through high many times and ensured the level was ideal, and drove around with no issues.

a few weeks past since flushing and I put my truck in High to perform some minor exhaust work below and I had left the truck parked in high overnight. When starting the next morning I received the beloved Check 4wd AHC System error. Techstream informed me it is due to a C1763 abnormal pump oil pressure. I am perplexed because prior to this the system was functioning better than ever in terms of lifting speed and ride quality. Maybe an air bubble developed in the system overnight or the pump somehow lost prime?

Right now I cannot seem to get the pump to run whatsoever, both on startup and through techstream active test. The pressure remains 0 MPA with no audible pump whine. The error code immediately returns upon clearing the DTC (even on accessory power) and I cannot get the pump out of 'safe mode'.

I just replaced the relay (to no avail), I've checked the fuses (I will replace them next just to be sure), and I am now mentally preparing to pull the pump and bench test. For anyone who has pulled the pump in the past, is it 100% necessary to remove the rear bumper? The 100 series reservoir/pump setup seems preferable at this stage...

Is there anything else anyone could recommend before going nuclear and pulling the pump and troubleshooting that assembly? I will do some additional electrical testing per the repair manual, but other than that I am losing hope.

Due to the system age, I would rather convert to a traditional spring setup and may do so in the future, but at this stage I don't have the money to cough up for upgrades, so I am hoping to get the current system reestablished.

Thanks you in advance,
Adrian

P.S. I also have noticed a code U1117 which I am unfamiliar with and have not yet dug into, I will troubleshoot this more before pulling pump as it may be related. It may have been caused by pulling AHC Relay

 

[AnyMal]

What was fluid level at when you were / are in high? Any chance it ran dry?

 

[AJLaz]

What was fluid level at when you were / are in high? Any chance it ran dry?

Fluid level was at max when in high so I don’t think so unless an air bubble somehow got trapped at the pump, or fluid entry became blocked

 

[AnyMal]

Fluid level was at max when in high so I don’t think so unless an air bubble somehow got trapped at the pump, or fluid entry became blocked

Hmm, thats not good either. Why would that have happened you think?

 

[AJLaz]

Hmm, thats not good either. Why would that have happened you think?

I filled it to the max line after bleeding, to ensure it wouldn’t run dry. still plenty of room in the reservoir the max is only slightly more than halfway up the tank

 

[AnyMal]

I filled it to the max line after bleeding, to ensure it wouldn’t run dry. still plenty of room in the reservoir the max is only slightly more than halfway up the tank

Well I guess it prob wouldnt have run dry at any reasonable reservoir angle.

 

[lx200inAR]

I’d check to make sure you are getting power at the pump. I think you were already headed down the right path with checking fuses/relays.

 

[AJLaz]

I’d check to make sure you are getting power at the pump. I think you were already headed down the right path with checking fuses/relays.

Yeah essentially it doesn’t seem to be getting any power, I replaced fuses and the relay with no change in behavior. It seems the system is cutting the power before the pump builds any pressure.. at this point I’m going to have to just pull it and rule out it being the pump itself. Oil pressure sensor seems to be functioning as I’ve seen some readings above 0, but I’m not sure if this sensor is replaceable anyways

 

[lx200inAR]

So when the pump is not engaged there will not be any pressure, but the static number is slightly above 0 .13mPa or something close to that). System pressure is maintained further downstream, so if the pump isn’t running there is no pressure on the sensor. If you are seeing a number higher than that, then the pump is engaging At least for a short period.

 

[AJLaz]

So when the pump is not engaged there will not be any pressure, but the static number is slightly above 0 .13mPa or something close to that). System pressure is maintained further downstream, so if the pump isn’t running there is no pressure on the sensor. If you are seeing a number higher than that, then the pump is engaging At least for a short period.

the highest I've seen in my current situation is 0.16, I'm guessing that may be the static number

 

[nwfl4runner]

Just trying to clarify a few things - when in HIGH mode your reservoir is at the MAX line? If you clear the DTC and immediately try to move the height to NORMAL the code returns?

 

[AJLaz]

Just trying to clarify a few things - when in HIGH mode your reservoir is at the MAX line? If you clear the DTC and immediately try to move the height to NORMAL the code returns?

correct and correct, the code comes back immediately upon clearing the DTC, even in accessory mode.
upon startup I am able to select a different height mode but the car gives the "Check 4WD AHC System" in under 1 second before the system changes height. I was able to put the car into low (accidentally) but now I am unable to go back up to a higher setting.

 

[nwfl4runner]

correct and correct, the code comes back immediately upon clearing the DTC, even in accessory mode.
upon startup I am able to select a different height mode but the car gives the "Check 4WD AHC System" in under 1 second before the system changes height. I was able to put the car into low (accidentally) but now I am unable to go back up to a higher setting.

Are you in low mode now?

 

[AJLaz]

Are you in low mode now?

yes, unfortunately

 

[nwfl4runner]

yes, unfortunately

I would check your reservoir level right now, I bet it is completely overfilled, which could affect pump performance. Are you shining a light from the spare tire area to check the level?

 

[AJLaz]

I would check your reservoir level right now, I bet it is completely overfilled, which could affect pump performance. Are you shining a light from the spare tire area to check the level?

It’s certainly too high right now with the suspension empty of fluid but I can’t set the level with it in low and that doesn’t really explain the initial failure.. and yes I am using a light from behind

 

[TeCKis300]

I know I've filled my reservoir pretty dang high before to purge it and it had no problem with it. I suspect that's not the issue as it doesn't care or can't tell unless it runs the reservoir dry. Not sure what caused the original C1763 issue, but it seems like the system is not actuating or responding due to some other error. Can you do a screen capture of the data list page?

I did a little sleuthing and I couldn't find any specific info on U1117 other than a generic CAN bus comms error

 

[AJLaz]

I know I've filled my reservoir pretty dang high before to purge it and it had no problem with it. I suspect that's not the issue as it doesn't care or can't tell unless it runs the reservoir dry. Not sure what caused the original C1763 issue, but it seems like the system is not actuating or responding due to some other error. Can you do a screen capture of the data list page?

I did a little sleuthing and I couldn't find any specific info on U1117 other than a generic CAN bus comms error

Here’s a screenshot from earlier, apologies on the poor quality.

I’m beginning to think the ecu isn’t sending the signal to the pump whatsoever but I don’t quite understand why. The fsm wasn’t particularly helpful on the u1117 code either, it basically said check for shorts.

 

[samaelestevez]

I have the exact same simptoms and techstream info as you... did you ever figure this one out?

 

[AJLaz]

Nope, I spent hours troubleshooting and ultimately deleted the ahc and put in billistien suspension. My ahc system was pretty rusty and not worth the money to replace components of. Basically what I deduced is that the system kicked into safe mode and was not sending current to the pump. I didn’t have a chance to fully strip out and test my ahc components but my guess is that the pump pickup either got obstructed or the pump was fried. I wasn’t willing to replace just the pump for the same cost as a complete traditional suspension, so I went that route.