AHC blinking OFF DTC 13, 18, 31, 32, 33, 34, 36, 43

[Barns]

Hey,

one day OFF start blinking, no obvious reason, we were not on trail, or had heavy load. I will try to describe my steps chronologicaly. techstream ordered, but still waiting for it. I would like to buy FSM, but I would like to be sure, it does contain AHC part, which was my question to seller on ebay, seller did not responded so far.

LC 100 4.2 2000 with AHC on it and rear diff lock, build fo central Europe

Spring 2021, work on suspension, no error presented at that time ...
- rear hight sensor changed, sadly not for brand new, but for another old one
- AHC fluid changed

End of summer 2021, OFF start blinking and hasnt stoped since than
- toyota technicians did only codes reading, which did not worked for their diagnostic, they saw count of 7 codes for AHC, but not exact codes
- another toyota technician confirm first information, but on the top of that, hight sensors shown differences between each other, so he managed AHC to level up from L to N by adjusting each of the sensor. than he did not know what to do
- I have find Ih8mud, thanks lord. suprarx7nut pointed me to FSM and techstream, I ordered techstream and gather as much of info about AHC as I was able from diiferent sources on internet, mainly PDF files of original FSM.
- I did reading of codes .. 13,18,31,32,33,34,36
- I did reset of ECU by pressing break 9* within 3s, than read exactly the same sequence of codes
- checked continuity between terminals on control valve assembly - OK
- checked connectors on ECU, unpluged main relay, if am I right it is main relay, photo below, unplugged the top connector, all looks nice, clean shiny
- did not tried to unplug other 2 connectors, I was not able to identify cables on the scheme, neighter on ECU photo below
- Do not know how to identify wich wiring to check on the ECU side to confirm control valve assembly - ECU wiring connectivity
- plug everythink back and read codes, reset unit by pressing pedal and read again with no change - 13,18,31,32,33,34,36, 43 as new which points to main relay, I wish I do not burn it somehow
- still thinking about the rear sensor, I read a lot here, and understand that dtc codes sometimes lie. maybe perform

I would like to ask for help, where to start? unplug batteries, check AHC fuse, test that main relay (PADDO described sound that its doing), change rear sensor directly? - this is something I could manage

Here I do struggle how to
check of AHC ECU that SHB and SHG 5V? easy to identify S8 connector, but which cable is 1 and 9?

Please some advice

Photos

Is this main relay for AHC?

how to identify cables on ECU side going to rear sensor?

 

[suprarx7nut]

I don't recognize those codes by heart, but anytime I see that many codes I think there's a major wiring or electrical fault with a relay/ECU, etc...

The AHC section will be in any of the LX models and the 06-07 US LC models. For non-US markets, I expect AHC to be included for any model which had AHC as an option.

If I remember, I'll try to grab my manual today in the shop and see if there's a common element that would trigger all those codes.

 

[Barns]

I have understanding of codes. I know how to test 13 and 31 - 36 according to FSM. What I miss is test for 18- the preasure sensor, and 43 - main relay

I did some progress over the wiring, now I finally knows what I am looking at, which cables to test eg. rear hight sensor X ecu side

 

[Barns]

I went thru code 13 - wiring ok, sensor ok, cleand up connectors just for sure. Did not solve the problem
Than I focused on control vavle assembly, I was able to measure resistance between the pins on it. So control valve assembly itself looks ok according to inspection procedure. Than wiring, I did measure resistance on all except pin 2. My first tought was this is my guy! Unfortunatelly I have two schemes with a little difference .. watch picture below. What a shame that I was nit able to unplug accumulator solenoid connector to check wiring here

Question for a million. Is it ok to not measure any resistance between Pin 2 on control valve assembly and pin 24 on ecu S9 connector? Or better scenario, this one line is down and it is a root cause of all that mess?

 

[saucebox]

It takes a moment to load, but just about every configuration of 100 series is in here: LC100 Workshop Manual - https://lc100e.github.io.

 

[suprarx7nut]

I went thru code 13 - wiring ok, sensor ok, cleand up connectors just for sure. Did not solve the problem
Than I focused on control vavle assembly, I was able to measure resistance between the pins on it. So control valve assembly itself looks ok according to inspection procedure. Than wiring, I did measure resistance on all except pin 2. My first tought was this is my guy! Unfortunatelly I have two schemes with a little difference .. watch picture below. What a shame that I was nit able to unplug accumulator solenoid connector to check wiring here

Question for a million. Is it ok to not measure any resistance between Pin 2 on control valve assembly and pin 24 on ecu S9 connector? Or better scenario, this one line is down and it is a root cause of all that mess?

View attachment 2866214

View attachment 2866215

I have a suggestion for you.

Focus on connector BI1. Do all your resistance checks of the control valve from that connector (probe the control valve side). That will tell you if the wiring from the valve running rearwards to the BI1 connector at the rear bumper frame rail is good. In two cases local to me (one which I diagnosed and fixed myself) that wiring section was to blame. It's an easy connector to get to and it has the conductors for the control valve and accum solenoid.

 

[Barns]

Hey @suprarx7nut ,

it took some time to unplug BI1 gently, and finaly I got understand ih8mud meaning . It had not make sense before as all of you love mudding with cars ... My wiring is broken between control valve assembly and BI1, you was right, I was not able to measure 3 out of 5 cables this time. My tought is that break has to be somewhere close to the BI1 and I broke 2 more cables during the unplug procedure.

what suprised me most is the condition of the connector inside ... all shiny clean gold white after 22 years

 

[suprarx7nut]

Hey @suprarx7nut ,

it took some time to unplug BI1 gently, and finaly I got understand ih8mud meaning . It had not make sense before as all of you love mudding with cars ... My wiring is broken between control valve assembly and BI1, you was right, I was not able to measure 3 out of 5 cables this time. My tought is that break has to be somewhere close to the BI1 and I broke 2 more cables during the unplug procedure.

what suprised me most is the condition of the connector inside ... all shiny clean gold white after 22 years

Yeah, despite being pretty accessible, that connector is real tough to undo.

That section of wire runs right on top of the frame over the rear tire. It seems to be a common failure point. I'm unsure if it's from rocks coming off the tires or what.

Glad to hear you found the failure point!

 

[Barns]

Hey,

finally repaired Cutted out 3 cm of Blue-Yellow wire, actually there was only blue dust inside .. and replace that part by new wire. This was located right about 10 cm from BI1.

When I turned the key, no OFF blinking, it immediately leveled itself a bit up. tried ALL modes since than, it rides, as it should, finally and again

MAny thanks @suprarx7nut

when I was under, I took a picture of my AHC pipe RL, and I do not know if that is too much? these housings are all dry on each damper, have a look ..

 

[uHu]

Good info here. I have/had the same problem, but I gave up on finding BI1, so I just added a new cable from the valve block, going forward and up through the firewall and in to the ahc ecu plug. Has been working OK for a year now. Now, with your help (Supra/Barns), I might give it another go. Holiday activity?
Good job, Barns.

My ahc shock pipes/connectors look about the same, but soaked with fluid film. Bloody road salt - can I sue the road authorities?

 

[suprarx7nut]

Hey,

finally repaired Cutted out 3 cm of Blue-Yellow wire, actually there was only blue dust inside .. and replace that part by new wire. This was located right about 10 cm from BI1.

When I turned the key, no OFF blinking, it immediately leveled itself a bit up. tried ALL modes since than, it rides, as it should, finally and again

MAny thanks @suprarx7nut

when I was under, I took a picture of my AHC pipe RL, and I do not know if that is too much? these housings are all dry on each damper, have a look ..

View attachment 2872709

That pipe looks to be ready for a leak. That's quite an annoying failure you'll have the opportunity to fix in the future.

 

[ClassyJalopy]

Adding to this very informative thread. Last weekend my AHC off light started blinking.
I checked the 50A fuse under the hood and found it blown. No big deal, replaced it and all was good for a couple of days.
But the off light started blinking again today and sure enough the 50A fuse is blown again!

Now I am thinking there is a short somewhere that's causing this issue. Unfortunately it is too damn cold to actually do anything abt it so I might have to park it until it gets warmer

 

[ClassyJalopy]

It warmed up to 16F today so threw on a new 50A fuse under the hood, fired up the techstream and found a single AHC error code: c1762 - oil pump pressure too high.
This is a little concerning since the AHC pump is brand spanking new in the last 5000 miles!
On to other measurements:
With the new fuse truck moved from L-N-H fine but a little slow. I measured abt 30 seconds for each transition!
Anyway, I think the culprit in my case might be high front pressure at 8.7 Mpa-g. Since my TBs are twisted in as much it would go so it might be time to get more stout TBs. I will continue this in my own build thread.