I'm with you on that. I suspect that with the high level of online antagonism towards AHC many folks are needlessly replacing it... They don't know neutral pressures so really don't know if major parts have failed.
AHC with harsh ride
- Thread starter kgrove
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- Thread starter
- #22
Could a harsh ride be caused by faulty electronics in the AHC system? How would I test for that (other than eliminating other causes)? For instance the sport/comfort switch... I don't recall it ever having much impact on the ride. Could it get stuck in a perpetually harsh mode?
Conceivably. Sensors - yes, valves yes (and more likely). Most perhaps all of these have DTC codes. So what are your reservoir graduations and neutral pressures? Any AHC DTCs? Comfort is "Lincoln Town Car" floatiness on mine. Generally mine stays on sport (thankfully we don't have Lincoln Town Cars down under!)
I have the same thing happening. No change when I switch over from sport to comfort.
I hooked up the Techstream and switched over. The ON/OFF values were changing so the switch itself does send a signal.
But that's about it.
- Thread starter
- #25
I searched for the AVS settings pdf you mentioned and couldn't find it. Do you mind re-posting or clue me in where it is?
Also - any guidance which fuse is for the AHC? None of the fuses are labeled and I don't want to just start pulling random 20A fuses until I get it right.
Unfortunately my laptop died (all Mac house so my XP laptop is ancient) so I can't get to TechStream. Everything so far is striking out so I need to go back and verify the pressures. I'm getting 10 graduations on my fluid from H to L, so it seems unlikely that my globes are bad. Kind of stuck doing basics until I can get that damn laptop functioning again, but in the meantime my truck rides like it has no shocks at all.
Aren't the fuses labelled on the inside of the lid? As I recall it is pressed in the plastic on my 2003 AU delivery LX.
The fuses in the cabin in my car are unlabelled as well.
uHu
Bridgeburner
Have you looked inside the lid?
Anyhow, the layout of the fuses is in the Owner's Manual.
Yes I have, nothing there.
And owners manual from a 12 year old car?
No way. i was surprised that all the keys were there, but no manual.
And owners manual from a 12 year old car?
No way. i was surprised that all the keys were there, but no manual.
I have an 03 LX with 100k. When I changed to new globes I immediately noticed I could feel all the small bumps in the road. I tested the system according to the manual and the 16 steps of dampening are working. I replaced the front shocks when they started leaking and did not notice any better ride. When the rear shocks leaked and i replaced them, the ride was much smoother. The truck does absorb large bumps well and the comfort/sport switch changes the ride, however I do not have ride quality very much better than most cars. Handling is good in turns since the AHC does not let the body lean. I did put the truck into diagnostics mode and drive around the block in soft mode just to see how it rode. No difference. There must be some other component involved. I am frustrated with this since it is hard to think it came from the factory like this. Sure wish someone could figure out what component exactly controls the ride quality. Pls do post you findings.
hoser
SILVER Star
Really, no label on the fuse boxes? That sounds odd. This might help but I imagine LHD to be different than RHD.
https://forum.ih8mud.com/showpost.php?p=7728626&postcount=9
https://forum.ih8mud.com/showpost.php?p=7728626&postcount=9
uHu
Bridgeburner
This is the fuse layout for 1998-1 to 2002-7 production. Doesn't seem to be any difference between LHD and RHD.
LHS kickpanel:
uHu
Bridgeburner
Engine room 1, - 1998-1 to 2002-7 production:
uHu
Bridgeburner
Engine room 2, - 1998-1 to 2002-7 production:
At risk of sounding like a round piece of worn out black vinyl... what are your neutral pressures?
- Thread starter
- #38
laptop back and semi-functional… DTC code C1718 present for the Pressure Sensor Circuit. Found this below elsewhere on this board (format is poor):
----
CIRCUIT INSPECTION
CIRCUIT DESCRIPTION
DI3GI−06
DTC
C1718 / 18
Fluid Pressure Sensor Circuit
This circuit is sending the data to detect the pressure output from the pump and to judge the abnormality of the fluid pressure by the ECU.
DTC Detecting Condition:
Either of the following 1. or 2. is detected:
1. When detecting the abnormal signal from the fluid pressure
sensor (Fluid pressure sensor terminal voltage of ECU is 0.3 V or less or 4.7 V or more) for every 0.01 sec. and that condition continued for 1 sec.
2. While the motor relay is non−operating, the condition that the fluid pressure exceeds 1 MPa (10.2 kg/cm2, 145 psi) continued for 10 secs.
Trouble Area:
- Fluid pressure sensor
- Fluid pressure sensor circuit
- Suspension control ECU
Fail safe function:
If trouble occurs in the fluid pressure sensor circuit, the height control is prohibited after the ECU has adjusted the vehicle height to the standard.
----
Suggestions where to go from here? I don't want to throw money at the problem and just start replacing things if I can further zero in on the problem. This is the first time I've dealt in anywhere near this kind of detail with Toyota codes and manuals (just got Techstream) and have more information than I know how to use.
BTW - my neutral pressures are a little high as well - 7.7 or 7.8 F and R. I'm going to try to fix the front this weekend with the torsion bars, but will have to wait on the rear and take it someplace that can install spacers or refresh the springs.
What is spec on the accumulator pressure?
----
CIRCUIT INSPECTION
CIRCUIT DESCRIPTION
DI3GI−06
DTC
C1718 / 18
Fluid Pressure Sensor Circuit
This circuit is sending the data to detect the pressure output from the pump and to judge the abnormality of the fluid pressure by the ECU.
DTC Detecting Condition:
Either of the following 1. or 2. is detected:
1. When detecting the abnormal signal from the fluid pressure
sensor (Fluid pressure sensor terminal voltage of ECU is 0.3 V or less or 4.7 V or more) for every 0.01 sec. and that condition continued for 1 sec.
2. While the motor relay is non−operating, the condition that the fluid pressure exceeds 1 MPa (10.2 kg/cm2, 145 psi) continued for 10 secs.
Trouble Area:
- Fluid pressure sensor
- Fluid pressure sensor circuit
- Suspension control ECU
Fail safe function:
If trouble occurs in the fluid pressure sensor circuit, the height control is prohibited after the ECU has adjusted the vehicle height to the standard.
----
Suggestions where to go from here? I don't want to throw money at the problem and just start replacing things if I can further zero in on the problem. This is the first time I've dealt in anywhere near this kind of detail with Toyota codes and manuals (just got Techstream) and have more information than I know how to use.
BTW - my neutral pressures are a little high as well - 7.7 or 7.8 F and R. I'm going to try to fix the front this weekend with the torsion bars, but will have to wait on the rear and take it someplace that can install spacers or refresh the springs.
What is spec on the accumulator pressure?
Kgrove,
IMO there is a 95% chance that your rear AHC globes (accumulators) are shot. 5% chance that the globes are ok and it is something else (shock body).
Neutral pressure is related to ride height and load but not really to globe health.
When the globes are shot the symptoms are precisely as you describe and there are no other normal reasons that have the same result.
It works like this…
1) Bump hits the tire
2) Tire flexes, absorbs a little shock, passes the rest through to the hydraulic fluid
3) Hydraulic fluid carries the shock to the damping valve body at whichever corner we are talking about
4) Hydraulic fluid in the damping valve body is connected to the AHC accumulator globe via the damping valves*
5) The AHC accumulate globe diaphragm compresses and rebounds to absorb the shock.
6) If pressure is too high for the AHC accumulator globe to handle then *after* the globe is fully compressed an over-pressure valve opens in the valve body to release the excess (~1500 PSI IIRC) pressure back to the tank.
So: if the ride is harsh on small bumps but ok over big bumps what is very likely happening is that:
a) on small bumps the AHC accumulator globes are unable to absorb the shock (little gas pressure left) and the bump is too small to open the over-pressure valve so your tires are the only thing in the system with any flex. Result - you can count every piece of gravel in your drive
b) on large bumps the AHC accumulator globes are unable to absorb the shock (little gas pressure left) but it does not matter because the movement is so large it opens the release valve. Result - since the valve is open the springs and damping valve are free to act and the truck floats. Note that if the globes are 100% done… zero flex…then pretty much any bump will cause overpressure so the truck will have a 1970s Cadillac ride (float and bounce)
Since this started after you hooked up a boat what likely happened is that the old rubber could not handle the strain and lost most of its remaining pressure.
The easy way to check this is to put the back of the truck on blocks, remove one of the globes, and look down the throat. When you take it off if you get a few tablespoons of fluid then its probably fine. If you get a pint or two then you know its shot…which you can confirm by looking into the throat. If the top of the diaphragm is pressing the bottom of the throat area (about an inch down) then pressure may be low but still usable (and of course that diaphragm pressure prevents it from holding much fluid). If it is not then pitch it and get a new one (the weak diaphragm allows the globe to fill up with a lot of fluid).
My rears went before the fronts and I had ~10 gradations high-low. If all four are gone then it will be lower, like 6-7. With new ones you'll see 13-14. Replacing the globes is trivially easy BTW.
The alternate (unlikely given your story) would be a bad shock body. The AHC globes are a wear item. The shock bodies are not. That would be much more of a pain to check and to repair also.
Best,
Jonathan
PS: I have not been on the forum for a while (work) so email me if I don't respond. jonathan@turnerclan.us
IMO there is a 95% chance that your rear AHC globes (accumulators) are shot. 5% chance that the globes are ok and it is something else (shock body).
Neutral pressure is related to ride height and load but not really to globe health.
When the globes are shot the symptoms are precisely as you describe and there are no other normal reasons that have the same result.
It works like this…
1) Bump hits the tire
2) Tire flexes, absorbs a little shock, passes the rest through to the hydraulic fluid
3) Hydraulic fluid carries the shock to the damping valve body at whichever corner we are talking about
4) Hydraulic fluid in the damping valve body is connected to the AHC accumulator globe via the damping valves*
5) The AHC accumulate globe diaphragm compresses and rebounds to absorb the shock.
6) If pressure is too high for the AHC accumulator globe to handle then *after* the globe is fully compressed an over-pressure valve opens in the valve body to release the excess (~1500 PSI IIRC) pressure back to the tank.
So: if the ride is harsh on small bumps but ok over big bumps what is very likely happening is that:
a) on small bumps the AHC accumulator globes are unable to absorb the shock (little gas pressure left) and the bump is too small to open the over-pressure valve so your tires are the only thing in the system with any flex. Result - you can count every piece of gravel in your drive
b) on large bumps the AHC accumulator globes are unable to absorb the shock (little gas pressure left) but it does not matter because the movement is so large it opens the release valve. Result - since the valve is open the springs and damping valve are free to act and the truck floats. Note that if the globes are 100% done… zero flex…then pretty much any bump will cause overpressure so the truck will have a 1970s Cadillac ride (float and bounce)
Since this started after you hooked up a boat what likely happened is that the old rubber could not handle the strain and lost most of its remaining pressure.
The easy way to check this is to put the back of the truck on blocks, remove one of the globes, and look down the throat. When you take it off if you get a few tablespoons of fluid then its probably fine. If you get a pint or two then you know its shot…which you can confirm by looking into the throat. If the top of the diaphragm is pressing the bottom of the throat area (about an inch down) then pressure may be low but still usable (and of course that diaphragm pressure prevents it from holding much fluid). If it is not then pitch it and get a new one (the weak diaphragm allows the globe to fill up with a lot of fluid).
My rears went before the fronts and I had ~10 gradations high-low. If all four are gone then it will be lower, like 6-7. With new ones you'll see 13-14. Replacing the globes is trivially easy BTW.
The alternate (unlikely given your story) would be a bad shock body. The AHC globes are a wear item. The shock bodies are not. That would be much more of a pain to check and to repair also.
Best,
Jonathan
PS: I have not been on the forum for a while (work) so email me if I don't respond. jonathan@turnerclan.us
Forgot to add the * for damping valves.
* the damping valve is just a bank of drilled holes that the fluid passes through on the way to the accumulator globe. The system selects one of the available hole sizes to restrict the fluid flow more or less depending on the orifice chosen. The restriction burns some of the energy as heat like the valving in a regular shock absorber. They are just flow restrictions though and cannot ultimately add any flex. This is why another symptom is that the system feels pretty much the same at any setting…and usually feels a little *better* with max damping.
* the damping valve is just a bank of drilled holes that the fluid passes through on the way to the accumulator globe. The system selects one of the available hole sizes to restrict the fluid flow more or less depending on the orifice chosen. The restriction burns some of the energy as heat like the valving in a regular shock absorber. They are just flow restrictions though and cannot ultimately add any flex. This is why another symptom is that the system feels pretty much the same at any setting…and usually feels a little *better* with max damping.
