Okay so I'm having some issues with my AHC and looking for some advice before I start buying more parts. Had this 2011 LX 18 months, purchased at 78k miles now at 90k miles. When I first test drove it and knew nothing about AHC, the AHC light would flash as if it were changing heights after pressing the switch to go up or down and nothing would happen. This was when testing it at the lot. Was not a Lexus/Toyota dealership and the salesman had no idea what AHC was either. After playing around with it for a while it eventually started working. Did a PPI at Lexus and told them about it, but it tested fine and had been without issue for about a year.
Now about 2 months ago saw a small leak in the driveway, long story short this height control tube had rusted out.
The vehicle has very litte rust and the rest of the lines look great. This height control tube is pretty high up against the body of the truck and when I visually inspected before purchasing I never got eyes on it. Two weeks ago after trying on my own I took it in and got the tube replaced. Lexus wanted $320 for parts and $800 for labor and said they weren't even sure if they could do it...... Purchased the parts for $200 and local shop did it for another $200. Since the repair, the truck has driven much smoother, I assume the damping was compromised because of the leak.
New issue is the truck won't go all the way into high and eventually regardless of what heights I'm changing between it will stop adjusting at all and just flash like it is changing heights normally but nothing happens. It will get stuck with the rear higher or sometimes one side higher. The rear seems to be much more responsive to height changes. If I turn the truck off for the day and start if the next day it will level off in normal mode. If I go to high it will move the rear up to what seems to be the normal height and start to move the front, but the front doesn't get the 2-3 inches higher, I'd say maybe an inch. After flashing High for a while it will finish up saying "N" on the dash. Now weird part is if I turn the truck off and then back on it will normally say "HI" after the restart without any changes in height. Even when it is working though it does not feel as smooth as before. For example when it was working flawlessly the front and/or rear would come up smoothly, both sides pretty much even with some minor left to right adjustments at the end before it would settle. Now I can usually feel the changes in all 4 corners if that makes sense.
In Techstream while conducting the active tests they all work great until eventually the system will become unresponsive again when testing any up or down function. No specific test will fail consistently. The gate valve, accumulators, etc. all open when tested. Only error codes I have received since the repair were last weekend, they were 1764 and 1765 which are due to hydraulic oil pressure getting too high (around 17 Mpa). This was during a test in Techstream raising the front by accumulator. This test pushed up the front higher then it would ever go under normal operation. Either way at the time it made sense because of the original issue of the rusted out tube. I figured contamination from the rust clogged the line going into the height control valve or clogged up the valves in the height control valve. Service manual says the same probable cause trouble areas for both codes:
- No. 1 height control valve (Each solenoid valve is stuck)
- Clog in the fluid line
- Suspension control ECU
That being said, I've watched the pressure since then and tested again today and pressure never went passed 12 Mpa. Exact same issues today during normal operation and during AHC tests in Techstream. No codes at all. Seems to do well moving between LO and N, but if I go to high it will not get there or if it does it won't go back to Normal height. It will drop a side and not the other or front and not the back, etc. I reset the ECU via Techstream and an hour long battery disconnect. Fluid has been replaced 3 times in the last 2 months.
I'm pretty far from a mechanic or an engineer so hoping someone can provide some expertise. At this point if I'm not convinced otherwise I'm going to assume there may be contamination in the height control valve no.1 and replace that since the rusted out tube that was replaced leads into it. I can get that part with the accumulator for around $300 on Ebay. Looking at the service manual it looks like a fairly basic removal and install that I can do myself. Planning to start with that and then maybe the ECU. I have attached my Techstream data for LO, Normal and HI if that helps anyone diagnose. I have done sensor lift and have bumper and winch on front. Thanks!
Now about 2 months ago saw a small leak in the driveway, long story short this height control tube had rusted out.
The vehicle has very litte rust and the rest of the lines look great. This height control tube is pretty high up against the body of the truck and when I visually inspected before purchasing I never got eyes on it. Two weeks ago after trying on my own I took it in and got the tube replaced. Lexus wanted $320 for parts and $800 for labor and said they weren't even sure if they could do it...... Purchased the parts for $200 and local shop did it for another $200. Since the repair, the truck has driven much smoother, I assume the damping was compromised because of the leak.
New issue is the truck won't go all the way into high and eventually regardless of what heights I'm changing between it will stop adjusting at all and just flash like it is changing heights normally but nothing happens. It will get stuck with the rear higher or sometimes one side higher. The rear seems to be much more responsive to height changes. If I turn the truck off for the day and start if the next day it will level off in normal mode. If I go to high it will move the rear up to what seems to be the normal height and start to move the front, but the front doesn't get the 2-3 inches higher, I'd say maybe an inch. After flashing High for a while it will finish up saying "N" on the dash. Now weird part is if I turn the truck off and then back on it will normally say "HI" after the restart without any changes in height. Even when it is working though it does not feel as smooth as before. For example when it was working flawlessly the front and/or rear would come up smoothly, both sides pretty much even with some minor left to right adjustments at the end before it would settle. Now I can usually feel the changes in all 4 corners if that makes sense.
In Techstream while conducting the active tests they all work great until eventually the system will become unresponsive again when testing any up or down function. No specific test will fail consistently. The gate valve, accumulators, etc. all open when tested. Only error codes I have received since the repair were last weekend, they were 1764 and 1765 which are due to hydraulic oil pressure getting too high (around 17 Mpa). This was during a test in Techstream raising the front by accumulator. This test pushed up the front higher then it would ever go under normal operation. Either way at the time it made sense because of the original issue of the rusted out tube. I figured contamination from the rust clogged the line going into the height control valve or clogged up the valves in the height control valve. Service manual says the same probable cause trouble areas for both codes:
- No. 1 height control valve (Each solenoid valve is stuck)
- Clog in the fluid line
- Suspension control ECU
That being said, I've watched the pressure since then and tested again today and pressure never went passed 12 Mpa. Exact same issues today during normal operation and during AHC tests in Techstream. No codes at all. Seems to do well moving between LO and N, but if I go to high it will not get there or if it does it won't go back to Normal height. It will drop a side and not the other or front and not the back, etc. I reset the ECU via Techstream and an hour long battery disconnect. Fluid has been replaced 3 times in the last 2 months.
I'm pretty far from a mechanic or an engineer so hoping someone can provide some expertise. At this point if I'm not convinced otherwise I'm going to assume there may be contamination in the height control valve no.1 and replace that since the rusted out tube that was replaced leads into it. I can get that part with the accumulator for around $300 on Ebay. Looking at the service manual it looks like a fairly basic removal and install that I can do myself. Planning to start with that and then maybe the ECU. I have attached my Techstream data for LO, Normal and HI if that helps anyone diagnose. I have done sensor lift and have bumper and winch on front. Thanks!
Last edited:
