I saw this 06-07 100 series. Obviously there is an AHC issue. Now I'm concerned about buying a newer 100 or LX470. Is that front low and rear high? Sorry for the sideways picture...
AHC Issue?
- Thread starter DallasFJ40
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Holy stinkbug Batman!
i had that problem - got me stuck in my garage 
for me it was just the rear sensor.
in the very least it's got a bad height sensor but with the rear sky high the neutral pressure would be sky high too and I would be concerned that the accumulators could be blown if the po had been driving it that way for a while. you cant do the gradations test to see if they're blown until the height is back to normal. so i'd assume they're bad.
using cheap prices for parts and doing the work yourself, iirc that's ~300 for the rear sensor (two more up front who knows if they're good) and 4x $500 for accumultors. so that's at least 2500 including ahc fluid, maybe more if the front sensors are bad or there are other problems.
If you want a good ahc system i'd factor in a few grand to get that sorted (again if you do work yourself - could be double of you pay others b/w parts markup and labor). If you plan to swap the suspension with non ahc then you can bargain down more and spend less to fix the problem - <2000 for the suspension you want (2000 for someone else to do your swap, and waay less if you do the swap yourself). Numbers not exact but i beleive they're in the ballpark.
for me it was just the rear sensor.
in the very least it's got a bad height sensor but with the rear sky high the neutral pressure would be sky high too and I would be concerned that the accumulators could be blown if the po had been driving it that way for a while. you cant do the gradations test to see if they're blown until the height is back to normal. so i'd assume they're bad.
using cheap prices for parts and doing the work yourself, iirc that's ~300 for the rear sensor (two more up front who knows if they're good) and 4x $500 for accumultors. so that's at least 2500 including ahc fluid, maybe more if the front sensors are bad or there are other problems.
If you want a good ahc system i'd factor in a few grand to get that sorted (again if you do work yourself - could be double of you pay others b/w parts markup and labor). If you plan to swap the suspension with non ahc then you can bargain down more and spend less to fix the problem - <2000 for the suspension you want (2000 for someone else to do your swap, and waay less if you do the swap yourself). Numbers not exact but i beleive they're in the ballpark.
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Yeah looks like the sensor. Why not just get one without AHC? Is that west village I see behind uptown pub?
- Thread starter
- #7
I just saw this one on the road. It was not for sale, but I would be embarrassed to drive it like that. It was a lady driving back from the grocery store...
Yes, that's exactly where I took the picture. McKinney and Lemmon. I've had plenty of cocktails there at uptown pub.
Yes, that's exactly where I took the picture. McKinney and Lemmon. I've had plenty of cocktails there at uptown pub.
She probably had no idea anything was wrong. The ahc just adjusts until the sensor is at the right position so the ahc thinks it is fine.
The place to you left in that pic the beginning to many a night that only have fuzzy memories of
The place to you left in that pic the beginning to many a night that only have fuzzy memories of
- Thread starter
- #9
I once lived within walking distance of Uptown Pub and the Loon. That was both good and bad. Good that I didn't need to drive there, bad that I didn't need to drive there. Thinking about it on this nice day makes me want to go hit that Uptown Pub patio.
Ouch $712.
Isn't this a DIY item for $50 if it's the pivot arm or $400 if the whole sensor is bad?
Isn't this a DIY item for $50 if it's the pivot arm or $400 if the whole sensor is bad?
Good question. It was acting up for about a month and for awhile would right itself if I turned the ignition off and on. It appeared electrical, not mechanical. The part was $400, so I was told, and I got a loaner for a couple of days which was worth something. It was $70K new and I have only paid for 30K service and tires, so I was extremely happy with the quote after reading about the costs to of completely replacing the AHC.
How would one know if it's just a bad sensor? Is there a test you can do? My Bro's AHC system is all the way down (on all 4 corners). Is that a chance it could just be 1 or 2 sensors failed? The funny thing is that there were no real warning signs.
Quick troubleshooting guide for mid-high mileage trucks:
Q1) If the ride is harsh but it goes up and down ok and you notice that the truck is adjusting height frequently; like every few stoplights.
A1) Bad spheres on whichever corner(s) is(are) hitting hard
Why? - Pressure in the spheres is so low that they have very little 'stroke' before they bottom out and their damping pressure will rise *very* quickly. As a result sharp edge bumps (curbs, potholes, pavement irregularities) hit harder than they should. Big slow bumps will still be absorbed ok since they will force the pressure relief to open, bypassing the spheres. Since the spheres are short-stroking the bypass is sending fluid back to the tank frequently, requiring the AHC to keep adjusting itself...you'll notice it bump up or down a little at lot more than it used to.
Q2) If you cannot tell the difference between full-comfort and full-sport damping modes -and/or- you find that the full-sport mode gives the most comfortable ride (the 'softer' modes feel too 'sharp') -and/or- you notice that the truck is adjusting height frequently; like every few stoplights.
A2) Low spheres on at least two corners...probably either front axle or rear axle. You are probably in a high-mileage truck with spheres that are still ok-ish but ready for replacement.
Why? Same as above but if you can't "feel" a specific corner then the pressure is not critically low but you are noticing a shorter stroke. When damping is set to a higher rate (e.g. 4 instead of 1) more of the energy from a bump is dissipated in the damping valves before it gets to the spheres. The sphere has to do less work and will bottom less frequently (maybe not at all). At the softer setting each bump will be only partly absorbed and then will turn hard at the end. i.e. 'Sport' will feel firm but smooth and 'Comfort' will will feel soft but harsh.
Q3) If the truck keeps bouncing after hitting a bump...i.e. it does not settle down immediately (as if you have no damping) and it feels basically the same in all modes.
A3) Two likely options:
i) Spheres completely 100% flat.
Why? If the spheres are all blown then every bump will force the pressure relief to open (no resistance) so the truck will act like it has springs but virtually no damping at all.
ii) AHC ECU problem, Damping actuator/electrical problem, or failed pressure relief valve
Why? Could be that the ECU actuators are non-responsive/locked into full-comfort (very little damping). All four actuators (not the spheres, the actuators that the spheres thread into) could be bad but that would be a large coincidence or seriously bad luck. More likely an ECU problem. This should throw a code though.
Q4) Truck won't go up or down at all or goes up or down *really* slowly
A4) Two likely options:
i) Bad pump
Why? If the pump goes bad then the system will not get to pressure or will get there too slowly for normal function. During normal driving hydraulic fluid gets recycled back to the tank by the pressure relief valve if a bump cannot be completely absorbed by the spheres (with new spheres it takes big bump, with nearly flat spheres pretty much everything trips the pressure relief). The pump replaces that fluid by recharging the central AHC damper (the cylinder on the DS rail) which recharges each corner.
Note that on a mid-high mileage truck there are probably other problems. I.e. if a truck is driven a long time with flat/bad spheres the pump will have to work a *lot* more frequently and the pumps don't seem intended for high duty cycle
ii) If it won't go up at all then look for a bad pressure sensor. A bad pressure sensor will lock out the pump completely.
iii) Pump lost prime. Could happen if the tanks was run too low during a flush or bleed operation.
iv) Bad ECU. A shot ECU may fail to signal the pump to start.
v) Way overloaded? If it's too heavy it goes to low and stays there...but this one is obvious.
Q5) One end is high or low or one end adjusts frequently but the ride quality is still fine.
A5) Bad height sensor. Usually in the rear it seems
Why? AHC uses the height sensors to tell it where it is. If a sensor is bad it will adjust to the bad signal. If a front sensor goes bad I believe you will get an AHC error code but the ride height will be correct or close to it (this happened on my truck). It seems that the ECU can compensate for one being out but will throw an error and probably flash the AHC dash light. There is only one sensor in the rear so if it goes bad the ECU has no comparative. Seems like fail high is the usual for a rear sensor.
These are really easy to replace and not terribly expensive. They are very simple devices and can be field repaired. If you are in a bind they can be disassembled with a philips driver and the little tracking fingers bent back into place and/or cleaned...in my case that lasted about another four months.
There are other explanations for every problem above but IMHO these are the most likely for a regularly used truck with 60+ thousand miles. If the truck has made it that far then any weird 'bad part' or 'bad assembly' problems should have been found and resolved already. The problems/solutions above are what I would consider the go-to's based on wear and tear failure. Based on this board and my own experience the spheres last slightly longer than a regular shock absorber does...75-100K miles. However unlike a regular shock absorber if they are not replaced when they get low the stress can cascade through the whole AHC.
IMHO/YMMV/open to comment/etc
jonathan
Q1) If the ride is harsh but it goes up and down ok and you notice that the truck is adjusting height frequently; like every few stoplights.
A1) Bad spheres on whichever corner(s) is(are) hitting hard
Why? - Pressure in the spheres is so low that they have very little 'stroke' before they bottom out and their damping pressure will rise *very* quickly. As a result sharp edge bumps (curbs, potholes, pavement irregularities) hit harder than they should. Big slow bumps will still be absorbed ok since they will force the pressure relief to open, bypassing the spheres. Since the spheres are short-stroking the bypass is sending fluid back to the tank frequently, requiring the AHC to keep adjusting itself...you'll notice it bump up or down a little at lot more than it used to.
Q2) If you cannot tell the difference between full-comfort and full-sport damping modes -and/or- you find that the full-sport mode gives the most comfortable ride (the 'softer' modes feel too 'sharp') -and/or- you notice that the truck is adjusting height frequently; like every few stoplights.
A2) Low spheres on at least two corners...probably either front axle or rear axle. You are probably in a high-mileage truck with spheres that are still ok-ish but ready for replacement.
Why? Same as above but if you can't "feel" a specific corner then the pressure is not critically low but you are noticing a shorter stroke. When damping is set to a higher rate (e.g. 4 instead of 1) more of the energy from a bump is dissipated in the damping valves before it gets to the spheres. The sphere has to do less work and will bottom less frequently (maybe not at all). At the softer setting each bump will be only partly absorbed and then will turn hard at the end. i.e. 'Sport' will feel firm but smooth and 'Comfort' will will feel soft but harsh.
Q3) If the truck keeps bouncing after hitting a bump...i.e. it does not settle down immediately (as if you have no damping) and it feels basically the same in all modes.
A3) Two likely options:
i) Spheres completely 100% flat.
Why? If the spheres are all blown then every bump will force the pressure relief to open (no resistance) so the truck will act like it has springs but virtually no damping at all.
ii) AHC ECU problem, Damping actuator/electrical problem, or failed pressure relief valve
Why? Could be that the ECU actuators are non-responsive/locked into full-comfort (very little damping). All four actuators (not the spheres, the actuators that the spheres thread into) could be bad but that would be a large coincidence or seriously bad luck. More likely an ECU problem. This should throw a code though.
Q4) Truck won't go up or down at all or goes up or down *really* slowly
A4) Two likely options:
i) Bad pump
Why? If the pump goes bad then the system will not get to pressure or will get there too slowly for normal function. During normal driving hydraulic fluid gets recycled back to the tank by the pressure relief valve if a bump cannot be completely absorbed by the spheres (with new spheres it takes big bump, with nearly flat spheres pretty much everything trips the pressure relief). The pump replaces that fluid by recharging the central AHC damper (the cylinder on the DS rail) which recharges each corner.
Note that on a mid-high mileage truck there are probably other problems. I.e. if a truck is driven a long time with flat/bad spheres the pump will have to work a *lot* more frequently and the pumps don't seem intended for high duty cycle
ii) If it won't go up at all then look for a bad pressure sensor. A bad pressure sensor will lock out the pump completely.
iii) Pump lost prime. Could happen if the tanks was run too low during a flush or bleed operation.
iv) Bad ECU. A shot ECU may fail to signal the pump to start.
v) Way overloaded? If it's too heavy it goes to low and stays there...but this one is obvious.
Q5) One end is high or low or one end adjusts frequently but the ride quality is still fine.
A5) Bad height sensor. Usually in the rear it seems
Why? AHC uses the height sensors to tell it where it is. If a sensor is bad it will adjust to the bad signal. If a front sensor goes bad I believe you will get an AHC error code but the ride height will be correct or close to it (this happened on my truck). It seems that the ECU can compensate for one being out but will throw an error and probably flash the AHC dash light. There is only one sensor in the rear so if it goes bad the ECU has no comparative. Seems like fail high is the usual for a rear sensor.
These are really easy to replace and not terribly expensive. They are very simple devices and can be field repaired. If you are in a bind they can be disassembled with a philips driver and the little tracking fingers bent back into place and/or cleaned...in my case that lasted about another four months.
There are other explanations for every problem above but IMHO these are the most likely for a regularly used truck with 60+ thousand miles. If the truck has made it that far then any weird 'bad part' or 'bad assembly' problems should have been found and resolved already. The problems/solutions above are what I would consider the go-to's based on wear and tear failure. Based on this board and my own experience the spheres last slightly longer than a regular shock absorber does...75-100K miles. However unlike a regular shock absorber if they are not replaced when they get low the stress can cascade through the whole AHC.
IMHO/YMMV/open to comment/etc
jonathan
