AHC debug... won't go HI (1 Viewer)

[TexFJ]

Here's a funny story, and I hope that others did the same thing so I don't feel too stupid.

First time I sat in an LX470, I tested to see if the transfer case was working as it should by switching the shifter from High to Low . I proceeded to give the PO a hard time because the transfer case was broken as the LED never switched from HI to LO on the Dash. (bad Toyota)

 

[IndroCruise]

Here's a funny story, and I hope that others did the same thing so I don't feel too stupid.

First time I sat in an LX470, I tested to see if the transfer case was working as it should by switching the shifter from High to Low . I proceeded to give the PO a hard time because the transfer case was broken as the LED never switched from HI to LO on the Dash. (bad Toyota)

Hi TexFJ,

I smiled at your story! Maybe IH8MUD needs a collection point for new Owners starting out so that mistakes already made can be discovered in what are becoming old vehicles.

My own story is more embarrassing. We had been travelling in the North Flinders Ranges, a rugged, remote but beautiful spot in South Australia. A mountain track required exploration. ‘Track’ is being generous. It was dry, rough, rocky and very steep. I had not been on a trip for a long time. I thought I had prepared very carefully. A small detail had been overlooked -- I actually had not checked the transfer case shifter. Your thread is headed “AHC debug... won't go into HI”. My problem was the opposite -- on the side of a hill I was discovering for the first time that no matter how much persuasion, the transfer case “…. won’t go into LO”. Unsure of the problem and with nowhere to turn, the only choice was straight ahead, uphill hoping nothing would break, and then down the other side hoping the brakes would not get too hot . We survived -- although one mis-step caused a damaged sill panel -- no sliders! The cause was nothing to do with AHC -- it was a frozen linkage due to corrosion -- but it taught me a lesson in paying attention to basic details! I wrote up and reported the cause and the fix -- attached.

 

[TexFJ]

I want to say that's funny but I'm sure it was scary and worrisome when you're on the trail. You've put a scare into me and I'm going to grease those up this weekend

 

[TexFJ]

Update: Changed the Globes with OEMs.

The old Globes came out and I thought I was going to see a big difference when measuring distance from the tip of the thread to where the diaphragm starts, but it was exactly the same as the new ones. I was a little worried, but then I installed the globes, flushed the system including accumulator and Voila. Around 13 notches counted between L and H. All is good with the world and the LX is no longer "squirrelly" on the road.

I also need to check if my pressures are good but I checked them earlier and adjusted the torsion bars. Perhaps I'll need to now fix the back pressure with a coil spring spacer, assuming it's tired.... thoughts?

 

[uHu]

I also need to check if my pressures are good but I checked them earlier and adjusted the torsion bars. Perhaps I'll need to now fix the back pressure with a coil spring spacer, assuming it's tired.... thoughts?

Check height and pressure first, then decide.

 

[IndroCruise]

Update: Changed the Globes with OEMs.

The old Globes came out and I thought I was going to see a big difference when measuring distance from the tip of the thread to where the diaphragm starts, but it was exactly the same as the new ones. I was a little worried, but then I installed the globes, flushed the system including accumulator and Voila. Around 13 notches counted between L and H. All is good with the world and the LX is no longer "squirrelly" on the road.

I also need to check if my pressures are good but I checked them earlier and adjusted the torsion bars. Perhaps I'll need to now fix the back pressure with a coil spring spacer, assuming it's tired.... thoughts?

View attachment 2354357

Hi TexFJ,

Seems like great progress. You already know the drill but to repeat it for good order ....

For best results, suggest always stick fanatically to the sequence counselled by uHu, PADDO and others over the years:

On level floor, vehicle at correct weight (fuel full, no freight and no people on board), steering straight ahead:

1. Check static cross-level at front (AHC and engine “OFF”), meaning, use Torsion Bar Adjusters to make front static heights equal so as to equalise torsion bar loadings (Note: Torsion Bar Adjusters are not used to ‘correct’ functional heights in AHC system). It is important to do this basic static ‘cross-levelling’ step first,
2. Check functional heights (AHC and engine “ON”) – if necessary, adjust heights using Height Control Sensor Adjusters – but switch engine OFF for safety during actual adjustment (Note: Height Control Sensor Adjusters cannot be used as a substitute for static ‘cross levelling’ required in Step 1 to equalise static torsion bar loads),
3. Check AHC pressures front and rear,
4. Adjust front AHC pressures using Torsion Bar Adjusters to change load share between front torsion bars and front AHC system to arrive well within correct front AHC pressure range,
5. Recheck both static cross-level equalisation AND functional heights after this step – fine tune both if necessary,
6. Review rear AHC pressures, if high, correct using new springs and/or spacers (Note: AHC rear springs are lightweight – low spring rate – become ‘tired’ and require replacement if old – five years is a guide but experiences vary -- I left mine in for 13 years but they definitely were passed their 'use by' date!),
7. After all changes -- recheck change in levels at AHC tank in “HI/LO Test” – this becomes the new base-line,
8. Consider long term vehicle use and set-up – if additional permanent weights are planned (drawers, rear bar, additional fuel or water tanks, sliders, roof rack, etc – decide whether stronger rear springs such as KING KTRS-79 and/or air bags inside rear springs should be used. (Note: From personal experience and as expected, when vehicle is empty and with KING KTRS-79 springs fitted, ride quality is slightly more firm but not unacceptable. AHC functions still work provided AHC pressure limits are not exceeded).

 

[TexFJ]

I checked pressures before I get into the other items. The front and back were both good, especially since I adjusted he torsion bars, but now after I replaced the globes my back shows normal for a while, equal to front pressure and then drops down to 2.5.

Did I not tighten the bleed valves? globes? Don't see much of a leak but granted it sill was pretty oily from the install. anything else that can drop the pressure on rear?

 

[IndroCruise]

I checked pressures before I get into the other items. The front and back were both good, especially since I adjusted he torsion bars, but now after I replaced the globes my back shows normal for a while, equal to front pressure and then drops down to 2.5.

Did I not tighten the bleed valves? globes? Don't see much of a leak but granted it sill was pretty oily from the install. anything else that can drop the pressure on rear?

View attachment 2355708

I will leave it to more experienced Members to diagnose your inconsistent rear AHC pressure reading.

If the measurement is reliable, it would suggest that the rear of the vehicle is too low -- meaning too much weight is being carried by the springs and not enough by the rear AHC system, or, perhaps something is binding mechanically (rear control arm bushes?), or, there is some other problem.

However, unreliable readings are experienced from time to time, so the first step is to take more readings.

In my own case, I have had similar but unreliable readings from time to time and wondered whether something is not working properly. Usually, I drive around the block to settle the suspension (and myself!), return, remeasure the physical hub-to-fender heights (both at static cross-level with engine and AHC "OFF", and, also functional physical hub-to-fender heights with engine and AHC "ON") to make sure that there is nothing ‘hanging up’ due to poor bushes or whatever. Then I reconnect my measuring equipment (in my case Mini ELMscan327 dongle plus reader app on an Android tablet) and very carefully drop to "LO", raise to "N", making sure that the pump has finished recharging 'globes' and Height Control Accumulator, and then check one more time that functional hub-to-fender heights are as expected, then read pressures. I usually persist until I have three measurements that are consistent. In my case, this usually persuades me that the "something not working properly" probably is me rushing too much!

In your case, if highly variable AHC pressure readings are obtained consistently while following the correct procedure and with hub-to-fender heights correct and weight correct, and if satisfied that there are no mechanical problems such as the rear upper and lower control arm bushes, then it may be time to consider the next level of possible problems.

The area around the ‘globes’ and Damping Force Control Actuators are likely to be be wet after changing ‘globes’ but, given the pressures involved, if you had a leaks at the ‘globes’ or bleeders, you would not be in any doubt from AHC fluid dropping to the floor. (Nevertheless, globes and bleeders should be tightened to the FSM-recommended torques but not overtightened. By the way, OEM ‘globes’ normally are supplied with two special washers fitted to each ‘globe’ as shown in the FSM – or look at the relevant Partsouq parts diagram).

A consideration might be whether the AHC time for "drop from N to LO" is significantly longer than the 3 to 8 seconds mentioned in the FSM, and, whether the AHC time to "raise from LO to N" is significantly longer than the 10 to 15 seconds mentioned in the FSM (with the Height Control Accumulator fully charged and in the stored state), and, whether any DTC’s are showing up such as DTC’s C1751 or C1762 (which may indicate pump problems or blockages). See half-way down my post #39 in this string for a link to a post by uHu on this topic.

If these kinds of issues are real, then it all starts to become complicated and expensive, so it is best to ensure that the ‘simple’ things are in good order first.

Hopefully other IH8MUD Members are able to give further guidance.

 

[LndXrsr]

Rear pressures can be variable for unclear reasons in different vehicles. Try measuring a few times with the temp sensor to the AHC pump disconnected (this is recommended in the FSM and seems to fix the spurious readings for many). It’s the connector closest to the firewall on the AHC pump if I remember right.

 

[IndroCruise]

Rear pressures can be variable for unclear reasons in different vehicles. Try measuring a few times with the temp sensor to the AHC pump disconnected (this is recommended in the FSM and seems to fix the spurious readings for many). It’s the connector closest to the firewall on the AHC pump if I remember right.

 

[LndXrsr]

@IndroCruise can I throw this pic in my AHC tutorial for reference?

 

[IndroCruise]

@IndroCruise can I throw this pic in my AHC tutorial for reference?

Definitely yes -- please feel free to use any of my stuff in your excellent ABCs of AHC if it helps. The pic concerned obviously is compiled from Partsouq pics.

See also the pics at this link -- or maybe consider appending the whole article:

https://vacc.com.au/TechOnlineV2/Resource/PDF/2057c78d-37b3-4725-b051-002f420895fe

The source is clearly marked on the document as the Victorian Automobile Chamber of Commerce (VACC) -- Victoria is a State in Australia. This document is freely available on the internet so presumably it is open file. Some engine bay pics clearly are Right Hand Drive but otherwise the document generally is representative. If parts of the document are used, maybe some attribution would be wise.

 

[LndXrsr]

Wow, fantastic document there. Will add the whole thing to my attachments post in the ABCs when I get the chance.

 

[TexFJ]

The picture is fine but the pressure sensor by the pump is not the one I'm interested in, right? I should be disconnecting the rear pressure sensor, per the pic below. Just need to find that sucker.

 

[TexFJ]

Never mind. those are the height sensors. Either the AHC system can open up each valve and sense the pressure (through the return valve/Accumulaor and valves) OR there is a pressure sensor built into either in the Level/Gate Valves or in one of the Damping Force Control Actuators.

one thing doesn't make sense in my case. If the pressure was really that low, wouldn't the rest be held up by the springs hence it would fall below normal height? Perhaps 2.6 PSI is enough. I need to compare heights to before globes were changed.

I can't imagine the one sensor works for fronts and then stops working for backs... IF there is only one sensor.

 

[TexFJ]

Measured the pressures a 3 more times today. And what do you know, it came back fine now.

One thing new I've noticed is when it gets to LO it seems it stops suddenly like it hits bottom. I'm thinking that this is just the valve closing suddenly as there's really nothing to hit, right?

I guess I'll skip any spring spacers as the pressures are fine. I'll start replacing bushings to get a tighter / stabler ride.

 

[IndroCruise]

Measured the pressures a 3 more times today. And what do you know, it came back fine now.

View attachment 2356831

One thing new I've noticed is when it gets to LO it seems it stops suddenly like it hits bottom. I'm thinking that this is just the valve closing suddenly as there's really nothing to hit, right?

I guess I'll skip any spring spacers as the pressures are fine. I'll start replacing bushings to get a tighter / stabler ride.

Patience rewarded! Pressures look good – assuming cross-levelling equalisation done and hub-to-fender heights are correct with AHC functioning. Curious to know whether disconnecting the temperature sensor per feedback from LndXrsr and FSM instruction made any difference when measuring rear AHC pressures in your case??

Not sure what to make of sudden stop at "LO" -- maybe check visually whether front is landing on the bump stops?

 

[uHu]

The picture is fine but the pressure sensor by the pump is not the one I'm interested in, right? ....

That pic of Component Locations is not for the 100 series.
Edit (added 5 hrs later):
The "misplaced" components are: ECU, Valve assembly, and the pump. The front position for the pump is right for the RHD version (and opposite side for LHD), while the "Alternative position" is for 150 or 200 series, I think.

 

[TexFJ]

I assumed it's just the RHD version.

 

[LndXrsr]

Glad you got some reasonable pressure readings. Oddly it is the temperature sensor on the pump that sometimes needs to be disconnected for unclear reasons. My method was always just take as many readings as possible until I felt like I could determine what was consistent/accurate and what was outlier.

Important to keep in mind for all that come to read this in the future that Techstream takes readings every second or two, so depending on how that timing lines up with your transition from L to N, it can result in quite variable readings. More repeat measurements = more precision usually.