AHC, here we go again, 2007 lx470 190k c1718 and c1713 (1 Viewer)

[aharlan001]

After 3+ years the AHC is striking again. On a short 15 min trip this morning I felt the rear end suddenly very stiff right away out of the driveway jarring the vehicle over small bumps, about 2 miles later the AHC off light started flashing. Upon arrival to my destination I found the rear end sitting on the bump stops. I inspected the system and saw no visible leaks at the globes, lines, or hydraulic shocks. Fluid level high in the reservoir. On the ride home the light continued to flash but the ride did improve. At home I found the car sitting at roughly the appropriate height. Quick research pointed to the rear height sensor so I took that off to clean and inspect but found the contacts inside to be very clean with minimal dirt inside. I put that back together and reinstalled to find no change. So next I pulled out techstream and I have a c1713 Rear Height Control RH Circuit Malfunction" and c1718 "Pressure Sensor Circuit" code. I'm leaning to the rear sensor but I should probably learn how to test the sensor batteries to confirm right? Additionally I could crack open and test the front two sensors too? I'm seeing online that despite the rear sag and rear height control code it does not necessarily mean the fault is there?

Background on the rig I have had it for a little over 3 years and a little under 30k miles. I baselined the AHC when I got it with new fluid and had a ton of issues when I got air into the system bleeding. Fortunately bleeding like 50x sorted that out after many hours of diagnostics. I checked the pressures just 2 or 3 months ago and was surprised to find the rear and front pressures still holding well. I also measured ride height on the front and both sides were to spec. Until today ride quality has been excellent.

Techstream data photo is sitting on a relatively level place with rear on bumpstops. Strangely after moving the vehicle from this spot to the driveway the rear end came up to it's normal height.

Please advise.

 

[Rhetoric]

Height sensors original?

They may look clean but they fail with age. Seems in most cases when these symptoms happen a new (Toyota only) height sensor solves it.

Partsouq or Impex is your friend.

 

[aharlan001]

Height sensors are original as far as I know. I just tested the rear sensor and it is giving me values to spec. 4.07 at one extreme (4.05 is spec for HI) 0.29 at the other extreme (0.45 is spec for LO) and 2.29 in the middle (2.25 is spec for N). I guess I can test the fronts too while I'm at it although I don't think I'll be able to get to it today. Based on the techstream readings this shouldn't be the problem though. If that is off the table I'll turn to c1718 next which according to the DTC code chart it is a fault in:

1. Pressure Sensor Circuit
2. Fluid Pressure Sensor Circuit or
3. Suspension Control ECU

Perhaps c1718 is causing c1713? Or maybe it's somehow one of the front sensors causing the rear sensor code and that is causing c1718? Seems unlikely since both front sensor readings in techstream are reasonable. The only problem that causes both codes is the Suspension Control ECU...

 

[aharlan001]

Last night I reinstalled the height sensor again after removing to test. Simultaneously I checked all the fuses under the hood and by the drivers left foot. I also unhooked the battery for an hour. Connected techstream again, cleared codes and they did not return immediately as they did before. Drove it 30 min this morning and it feels appropriate on the road and ride height looks correct. Not sure what to think. I plan to clean and test the front sensors as well as test the ahc ecu and pump pressure sensor pert fsm with multimeter. If those all test fine and the problem returns I plan to replace the rear sensor although it tested fine. I have one on order. Any thoughts? I have not tried to operate the system to H or L this morning since I don't have time to mess with it for a few days and it's riding fine now so I don't want to press my luck.

 

[Coin]

I don’t recall seeing many leople solve this problem with a new sensor. I had similar/same symptoms and new globes fixed it right up. Not to mention a superior ride as well.

Do you know if the globes have ever been replaced?

 

[IndroCruise]

Last night I reinstalled the height sensor again after removing to test. Simultaneously I checked all the fuses under the hood and by the drivers left foot. I also unhooked the battery for an hour. Connected techstream again, cleared codes and they did not return immediately as they did before. Drove it 30 min this morning and it feels appropriate on the road and ride height looks correct. Not sure what to think. I plan to clean and test the front sensors as well as test the ahc ecu and pump pressure sensor pert fsm with multimeter. If those all test fine and the problem returns I plan to replace the rear sensor although it tested fine. I have one on order. Any thoughts? I have not tried to operate the system to H or L this morning since I don't have time to mess with it for a few days and it's riding fine now so I don't want to press my luck.

Intermittent C1713 combined with erratic rear height behaviour as described means a definite problem in the Rear Height Control Sensor circuit, meaning any of:

• the Height Control Sensor, or,
• the connector, or,
• the harness.

The fact that removal and re-installation fixed the problem, at least for now, suggests an erratic contact and possibly intermittent open circuit or intermittent short circuit somewhere at some location within the Sensor or within the connector or within the harness.

After ~17 years of continuous movement every time the vehicle is driven, wear of the carbon track within the Sensor and/or wear or loss of pressure by the brushes which run on the carbon track (either causing constant or intermittent open of high resistance circuits), and/or moisture/dirt causing ‘tracking’ (short or low resistance circuits) within the Sensor are all eventually inevitable in this ‘wear item’.

Suggest close inspection of the connector and the wiring leading into the connector.

Also suggest replace the Rear Height Control Sensor for reliability as planned anyway. At ~17 years of age the Rear Height Control Sensor has had a fair innings in a hostile environment and it is well past its best. Strongly recommend using only OEM replacement Sensors (TOYOTA/LEXUS or possibly AISIN) to avoid the short life of the various subsitutes and fakes.

The Front Height Control Sensors are not implicated in the symptoms described -- but in 2024, they are closer to end-of-life than they were 14 years earlier in 2007 ex-factory. The intended further inspection/testing of Front Height Control Sensors is warranted anyway.

By the way, a faulty or damaged Height Control Sensor may transmit signals within the FSM-specified range of timing and within the FSM-specified voltage range of 0.3 volt to 4.7 volt, but at the wrong positions, meaning that the actual height of the vehicle is incorrect. Provided the voltage signal is acceptable to the ECU, there will be no DTC even if the vehicle height is incorrect – so observation of vehicle behaviour is an important part of diagnosis.

It is not clear why C1718 is showing -- suggest check the connector and wiring and test the Pressure Sensor at the AHC Pump, as intended. This is the only Pressure Sensor in the AHC/TEMS system on LC100/LX470.

ECU problems are possible but seem highly unlikely in the absence of other symptoms.

 

[aharlan001]

Intermittent C1713 combined with erratic rear height behaviour as described means a definite problem in the Rear Height Control Sensor circuit, meaning any of:

• the Height Control Sensor, or,
• the connector, or,
• the harness.

The fact that removal and re-installation fixed the problem, at least for now, suggests an erratic contact and possibly intermittent open circuit or intermittent short circuit somewhere at some location within the Sensor or within the connector or within the harness.

After ~17 years of continuous movement every time the vehicle is driven, wear of the carbon track within the Sensor and/or wear or loss of pressure by the brushes which run on the carbon track (either causing constant or intermittent open of high resistance circuits), and/or moisture/dirt causing ‘tracking’ (short or low resistance circuits) within the Sensor are all eventually inevitable in this ‘wear item’.

Suggest close inspection of the connector and the wiring leading into the connector.

Also suggest replace the Rear Height Control Sensor for reliability as planned anyway. At ~17 years of age the Rear Height Control Sensor has had a fair innings in a hostile environment and it is well past its best. Strongly recommend using only OEM replacement Sensors (TOYOTA/LEXUS or possibly AISIN) to avoid the short life of the various subsitutes and fakes.

The Front Height Control Sensors are not implicated in the symptoms described -- but in 2024, they are closer to end-of-life than they were 14 years earlier in 2007 ex-factory. The intended further inspection/testing of Front Height Control Sensors is warranted anyway.

By the way, a faulty or damaged Height Control Sensor may transmit signals within the FSM-specified range of timing and within the FSM-specified voltage range of 0.3 volt to 4.7 volt, but at the wrong positions, meaning that the actual height of the vehicle is incorrect. Provided the voltage signal is acceptable to the ECU, there will be no DTC even if the vehicle height is incorrect – so observation of vehicle behaviour is an important part of diagnosis.

It is not clear why C1718 is showing -- suggest check the connector and wiring and test the Pressure Sensor at the AHC Pump, as intended. This is the only Pressure Sensor in the AHC/TEMS system on LC100/LX470.

ECU problems are possible but seem highly unlikely in the absence of other symptoms.

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Thanks for weighing in, sounds like I'm on the right track. I feel like the two have to be related or ine is causing the other to trip. After clearing the codes the first time they both came back immediately. The height sensor code showing up just a second or two before the pressure sensor code. There is one thread for someone with a rhd vehicle overseas who had the pressure sensor code with a height sensor code (not the back) he went down a rabbit hole with the ahc for it to end up being a bad alternator. Per the fsm the only thing that can cause fault in both is the ecm but as you've alluded failure here this is most unlikely and although the fsm documents how to test I've not seen any thread on here documenting failure of the ecm. Seems like the pressure sensor code is rare to begin with and height sensor codes and height sensor failure relatively common...

 

[suprarx7nut]

Last night I reinstalled the height sensor again after removing to test. Simultaneously I checked all the fuses under the hood and by the drivers left foot. I also unhooked the battery for an hour. Connected techstream again, cleared codes and they did not return immediately as they did before. Drove it 30 min this morning and it feels appropriate on the road and ride height looks correct. Not sure what to think. I plan to clean and test the front sensors as well as test the ahc ecu and pump pressure sensor pert fsm with multimeter. If those all test fine and the problem returns I plan to replace the rear sensor although it tested fine. I have one on order. Any thoughts? I have not tried to operate the system to H or L this morning since I don't have time to mess with it for a few days and it's riding fine now so I don't want to press my luck.

A visual inspection is invalid on the height sensors. You can have a completely dead sensor that looks 100% brand new perfect. Alternatively you can have a perfectly good and reliable sensor with some imperfect looking internals. Even with the voltmeter, you need to ensure it's measuring smoothly which is tough with a typical DMM. You really need an oscilloscope or something so see if the sensor is reacting smoothly.

Make sure to only use genuine Toyota/Lexus sensors. Nothing aftermarket is worth the time, IMO.

Your Techstream results tell me you've either got a dead sensor or a bad circuit. Both are among the top failure points for AHC. If the problem persists after sensor replacement, I'd start running through very careful and thorough circuit tests.