AHC stuck in low and flashing "OFF" - how to test?

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R

rwheelz

Joined
Aug 28, 2006
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My AHC is stuck in low and if you try to raise the truck, it gives up and flashes the "OFF" light for the AHC.

132k miles. AHC fluid flushed at 80k miles. Ironically, I have two new cans because I was just about to do it again!

Nothing comes up when scanning the ECU - I am guessing the AHC system runs off a different ECU...? Meaning I would have to pay Lexus to diagnose the system...? Nearest dealer is 550 miles away.

Is there any way I can test the system at home to determine the problem? I tried resetting the ECU to no avail. The pump is running, I can hear it, feel it, and it is getting hot as I try to make it raise the vehicle. The fluid is not moving and the height is not changing. The truck rides like crap when stuck in LOW mode. The AHC fuses are intact.

I DID search and there are many AHC threads, mostly telling people how to flush the system. I cannot even do a flush, as I cannot get the vehicle to raise. I would like to know if I require an expensive fix, because if so, I may opt to just scrap the AHC and buy some regular struts.

Suggestions?
 
I'm of no help, however a Toyota dealership should be able to diagnose since newer 100's came with AHC. I hope one is closer than 550 miles away! Thats insane. Honestly your best bet is to swap out the suspension. Therefor you don't have to worry about a 550 mile drive, or a $550 repair bill to fix a sensor. Which probably means you have a bad sensor (seriously)
 

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Jaybob said:
What was the solution? I am having the same problem.
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Your system has gone into fail safe mode and this could be for any number of reasons: overloaded, failed sensor, etc. Use the procedure provided at post#3 to try and extract codes and we can go from there.


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PADDO said:
Your system has gone into fail safe mode and this could be for any number of reasons: overloaded, failed sensor, etc. Use the procedure provided at post#3 to try and extract codes and we can go from there.


Sent from my iPhone using IH8MUD Forum
Click to expand...
I will look into getting that diagnostic tool. After two days, the pump succeeded in raising it back to N and is staying there. I will be able to get it to the shop next week and they can take a look at it.

Now to research aftermarket parts because I don't have any need to raise and lower.

J
 
Jaybob said:
I will look into getting that diagnostic tool. After two days, the pump succeeded in raising it back to N and is staying there. I will be able to get it to the shop next week and they can take a look at it.

Now to research aftermarket parts because I don't have any need to raise and lower.

J
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Good you've got it back to N. Not sure what diagnostic tool you're referring to; the "hand held tester" is what we collectively refer to as "TechStream with mini vci" and that requires a laptop to run, the other SST is a simple shorting wire. Nothing technical, some use a paper clip, literally, a short length of insulated copper wire, ends stripped back, works perfectly. Anyway, see what your dealer says next week. There is no shortage of conventional replacement options for your AHC/AVS if that's the direction you choose.


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Jaybob said:
Ran the techstream. Got codes
C1751
C1763
Beginning research now :-)
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It's possible the 51 code is also causing code 63 so try and eliminate 51 first. What's your neutral pressure? A cause of 51 is inadequate torsion bar support to the AHC system. Use TechStream to read your neutral pressures and adjust your torsion bars if necessary to get 6.9 Mpa front pressure. Clear all codes and test again.


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I wasn't sure what the process was for getting the neutral value, but when I raised it to high,
Front 9.9
Rear 8.1
Accumulator 10.4

Back to neutral
Front 7.0
Rear 8.4
Accumulator 10.4

I didn't want to go to low since I was stuck there before. Do I need to, or does this show that I'm really close?
 
Ok, I raised from L - N and was high. Adjusted torsion bars but could only get it down to 7.4 mpa. It stayed at 7.4 from 3-6 full turns.

Should I leave it at 6 turns or drop it back down to 3? It seems to be riding just fine.

Flushing the system next.

Thanks
 
Jaybob said:
Ok, I raised from L - N and was high. Adjusted torsion bars but could only get it down to 7.4 mpa. It stayed at 7.4 from 3-6 full turns.

Should I leave it at 6 turns or drop it back down to 3? It seems to be riding just fine.

Flushing the system next.

Thanks
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If you raise the vehicle to H it takes a little less effort to put turns onto the TBs. I'd go for a couple more turns to get the front closer to 7Mpa. Flushing new fluid through is good too. When you're done take it for a quick drive and recheck your neutral pressures from L to N, you want, ideally 6.9 front and 5.6 - 6.4 iirc for rear. If you haven't yet you want to clear the DTCs and hopefully you've fixed your problem.


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I was just reading more on the torsion bars - I was getting scared I should let them out. It has 100k and I'm pretty sure PO never adjusted.
 
Jaybob said:
I was just reading more on the torsion bars - I was getting scared I should let them out. It has 100k and I'm pretty sure PO never adjusted.
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Crank away to get that front pressure down to where you want it, you won't break the TBs. I would not be surprised at all if the PO didn't adjust TBs for neutral pressure, or change fluid for that matter. It escapes me why these systems tend to be so neglected. Let us know how things work out.


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