AHC bumpy and rough ride (1 Viewer)

[goldigital]

Hi Guys,

I literally "hit the wall" in terms of trying to find out what's wrong with the ride quality, it was never velvet like but WAY better than in the recent months.
I am dealing with 06 LX with 104K miles, and the codes I get are DTC 1721 and 1723 which translates to front and rear damping force actuator circuit problem.
I have flushed, bleed and verified the AHC fluid levels, and have about 10-11 marks/graduations. Checked my damping force actuators resistance. Did the 16 step (walk around and bounce each corner) test. Nothing above indicated obvious fault. Checked all harnesses, connectors, etc
Replacing globes would be next logical step, but! ... I have been reading up that switching the AHC (HI to LOW) would have to be less than 7 graduations for the globes to be bad.
How can I check/verify the suspension ECU operation (resistance or voltage measurements) ???

I appreciate your input !!!

Cheers everyone!

 

[BillZ260]

Changing the ride settings does nothing? Comfort * * * * Sport

Maybe that switch went bad?

 

[geanes]

What are your neutral pressures? Have you tested them on Techstream? There is a fairly precise window for setup in order to maximize the potential of the AHC. Fronts should be around 6.7-6.9 and rear should be between 5.8-6.7 I believe. The AHC is a "balanced" system where the springs (rear) and torsions bars (front) take on around 60% of the spring load whereas the AHC takes on the 40% balance. If those are out of whack, your ride will be less than ideal. Your springs/TBs may be old and losing their spring rate which would absolutely impact ride quality.

 

[goldigital]

BillZ260: No difference in switching Comf ... Sport :-( .... chance for switch going bed are slim, but possible.

geanes, Yes, forgot to mention my neutral pressure which I checked about last year was is 7.1 fr and 6.5 rear. Not ideal i know but didn't suspect this to have such big difference in dampening force. Will redo the neutral pressure check again.

So, globes should be fine you think ???

Thanks for your help!

 

[goldigital]

Pulled the trigger and got myself 4 brand new toyota globes, to improve rough and bouncy ride, and after replacement shockingly didn’t see much ride improvement?!?!? ... which means I have old ones that were just fine :-( ... i listened to the Toyota dealer who said it is sure thing globes are gone! Anyway, I have new globes and still trying to get SOFT ride in Comf position. I see difference between Comf and Sport switch modes, and it shows in Techstream.
I did the neutral FR and RR pressure check. Adjusted TB’s to get the less front pressure, was sitting on the 9.0 mark, now I’m 7.0-7.2 for front. Evidently my trouble codes are still there, as they were before Globes replacement. I will check the Ohms on the Damping force actuators in the next day or so to get more info ...

Do you guys see anything particularly troublesome on my LIVE screen I should be looking at? ... any $.02 is appreciated !!!

Cheers!

Cheers!

 

[PADDO]

You’ve got over current system faults in both front and rear damper control circuits. It’s caused your variable damping control to be suspended - note your front and rear step values should be 8s in this situation and not 6 & 7. This fault isn’t related to damper accumulators or preload neutral pressure at all, its electronic/control and it’s either a common fault in your damper assemblies harness (very very unlikely all four stepper motors have developed low resistance or ground faults) or the ECU. Do you have the FSMs and EWD?

Could be worth pulling the 20A fuse to see if that resets the ECU (I’ve had a locked up ECU fault that wouldn’t clear any other way) otherwise try clearing faults in Techstream and repeating the 16 step damper test with Techstream hooked up. You will see both step values start at 1 and progress with the brake pedal push if the damping system is functioning properly. You can also drive with Techstream hooked up and watch, in a functioning system, the damper step values change with speed and road conditions.
If you’re following the 16 step damper test from the FSM it says to turn ignition on, you actually have to start the engine and do the test with the engine running.
If the faults won’t clear then you’ll need to determine if your harness is shorted and if it checks out properly then all that’s left is the ECU.

 

[goldigital]

Thanks Paddo ! I have to do the things you said, I also didn’t think FR and RR actuators motors died at once in the 2006 model.

... I don’t have full ccess to FSM just single pages, ... working on it!
THX again!!!

 

[goldigital]

Re-did the live active 16 step test, drove around and my suspension was rock hard, and Techstream showed no difference in STEPS count when pressing brake pedal, was stuck on 6 and 7. Removed 15A AHC-B and 20A AHC-IG fuse for good 2hrs (let the capacitors drain) with no luck (one thing I noticed the fuse for AHC-IG was 15A not 20A as it should be ... ???? wish the truck could speak!!!!! ... this tells me that the previous owner had to replace it with 15A. All fuses are good. Next I'll be checking harnesses from actuators to ECU and digging into ECU location and looking at ECU's connectors.

 

[MongooseGA]

Anything new on this?

These are codes that only show in techstream, correct? You're not getting any kind of indicator on the dash or anything for it?

Replaced my globes recently as well and still have a crap ride after checking pressures and adjusting TBs. Interested to see what else you find.

 

[goldigital]

nothing on the dashboard, all Hi and Low works flawlesly i’m trying to figure it out where my techstream dtc 1721 and 1723 are coming from. So far i know i have a short circuit in the harness ... will be chasing this again soon!

 

[goldigital]

Just a quick update, the reason for my LX to have a firm ride, because my AHC was in a fail safe mode, not sending signals to actuators due to one of the junction connectors (namely BG1 and BG2) had short to ground state. I also had DTCs 1721 and 1723 in the techstream.

After “few” long nights I located the connectors and replaced them with just splice (solder, heat shrink, and cable shroud) ... and now truck rides like new again!

Lookup my other posts for more details.

Cheers!

 

[Stricmic000]

found related post about exhaust leak melting connectors on frame rail behind right rear wheel well, disreguard

 

[saudi]

Just a quick update, the reason for my LX to have a firm ride, because my AHC was in a fail safe mode, not sending signals to actuators due to one of the junction connectors (namely BG1 and BG2) had short to ground state. I also had DTCs 1721 and 1723 in the techstream.

After “few” long nights I located the connectors and replaced them with just splice (solder, heat shrink, and cable shroud) ... and now truck rides like new again!

Lookup my other posts for more details.

Cheers!

where are these 2 juctions on the car

 

[Stricmic000]

where are these 2 juctions on the car

Search my name, i posted images of fsm documents, cant be more help atm sry

 

[saudi]

Search my name, i posted images of fsm documents, cant be more help atm sry

Thanks

 

[Scrappy]

Hi everyone, I currently have code C1723 pulled from Techstream. I’ve thoroughly read through this thread but still feel lost given that I have no solid knowledge of electrical concepts. Can someone give more detailed context on how to go about diagnosing this issue, or am I better off trying to consult the dealer to help me out?

 

[suprarx7nut]

Hi everyone, I currently have code C1723 pulled from Techstream. I’ve thoroughly read through this thread but still feel lost given that I have no solid knowledge of electrical concepts. Can someone give more detailed context on how to go about diagnosing this issue, or am I better off trying to consult the dealer to help me out?

It's likely a wiring problem. That's a tough thing to troubleshoot if you don't know wiring very well. A Toyota or Lexus dealer will probably refuse to even attempt to troubleshoot.

You'll want to learn to DIY this troubleshooting or find a mechanic that specializes in wiring and has an EWD for a 100 series.

This is all labor so it's free if you want to figure it out (minus the cost of a DMM and the EWD if you don't already have them). Could be $1000+ to pay a pro.

 

[Scrappy]

It's likely a wiring problem. That's a tough thing to troubleshoot if you don't know wiring very well. A Toyota or Lexus dealer will probably refuse to even attempt to troubleshoot.

You'll want to learn to DIY this troubleshooting or find a mechanic that specializes in wiring and has an EWD for a 100 series.

This is all labor so it's free if you want to figure it out (minus the cost of a DMM and the EWD if you don't already have them). Could be $1000+ to pay a pro.

Thanks for the reply. I have no problem learning to DIY this, but I’m uncertain as to whether or not I’d be able to understand the DMM or EWD without a foundational understanding of wiring first. Do these documents aid in the understanding or should I get that foundational knowledge beforehand?

 

[Scrappy]

Thanks for the reply. I have no problem learning to DIY this, but I’m uncertain as to whether or not I’d be able to understand the DMM or EWD without a foundational understanding of wiring first. Do these documents aid in the understanding or should I get that foundational knowledge beforehand?

So I lucked out and was able to find the issue by studying the wiring diagrams that were posted from a separate thread. The bracket that was holding the harness that runs across the frame in the rear had rusted, so the harness fell and sat about a quarter inch away from the exhaust pipe. The exhaust pipe melted those wires. As Paddo had astutely observed, the majority of these C1721/23 codes seem to be as a result of the exhaust. In my case it wasn’t a leak, but nonetheless, a result of an exhaust heat source. Now I just have to figure out how to get these wires repaired myself!