I know it's been some months since I posted this but I finally got around to doing actual work on my AHC system.
A few updates: I acquired a copy of TechStream and bought an old 32bit windows laptop to run it. Works great and I love the idea of being able to tweak everything.
I was getting codes that both AHC front sensors were bad. My AHC OFF light was blinking constantly. Well, after replacing the sensors, the OFF light no longer blinks. A small success that I'm happy about. Hopefully that means I did the right thing.
My current situation: While my OFF light no longer blinks, the system still won't go into HI or LO. When I hit the switch, the green indicator light blinks and will keep blinking unless I cancel it and select neutral again. My doors are all closed and the door switches all work so it's not my doors. I have not adjusted the new sensors to be zero yet either. I just took them.out of the box and installed them. The way the truck sits doesn't seem to have changed at all so it hasn't self adjusted to the new readings which I believe it should do because the new height sensors are not even close to the same reading. They're an inch different in reading.
When I have techstream open to view live data, I'm getting good readings from all of the height sensors. But, all of the pressures are reading 0's across the board. I would think there has to be some pressure in the system or else I'd be sitting stuck in the low position, right? Also, I feel like the comfort control is actually working now. It could be in my head, but it definitely makes a difference on my butt-meter.
My question now is, should I be looking at possibly the system's pressure sensors? Or do I need to adjust the height sensors first to get them reading the same number?
I may have missed this information in some of my reading but you'll have to take it easy on me. There's a TON of information to read through. I read through the threads linked above, but I couldn't seem to find the information I'm looking for.
I was hoping to get the system bled and refilled bit I if the thing won't go into HI or LO, I don't want to chance bleeding the system, just for it to be stuck bottomed out.
I'll try to attach a pic of my readings on techstream and maybe somebody more familiar with the normal readings can see if something doesn't add up.
View attachment 2734289
Seems like you are making very good progress! You have made Techstream work and now you can see into the Electronic Control Unit (ECU) which controls the Active Height Control (AHC) and Toyota Electronic Modulated Suspension (TEMS) systems and also you can see various other items of information.
Good that you have posted the Techstream screenshot. That helps a lot because we can see the details you can see and can move forward
Physical information also is important.
The details requested by
@ramangain will help.
In addition, I would request the actual hub-to-fender distances at each of the four wheels, measured with a tape-measure under the same conditions for any AHC test work -- vehicle on a level surface, steering straight ahead, no persons or other loads in the vehicle. These physical measurements are just as important as anything on Techstream. Among other things, they indicate how close to cross-level the vehicle may or may not be at the front. This helps in interpreting the Height Control Sensor readings and diagnosing problems.
Cross-levelling is vital to setting up the system properly. It is done only with the front torsion bar adjusters (and not the Sensor adjusters) in accordance with the attachment below.
It is good practice to clear the Diagnostic Trouble Code (DTC) which is showing on Techstream screenshot at the “Number of Trouble Codes” line. Then start up the vehicle and Techstream again. The point here is that if the DTC is historical then you want that deleted and out of the way because it will cause confusion. On start-up, any
current DTC’s will show again and then you know that you are dealing with current information. As mentioned by
@ramangain, it is important to know what current DTC’s are showing. The DTC can be identified from the codes shown in the “DIAGNOSTICS” section of the Factory Service Manual (FSM) – see reference near the end of Post #7 in this thread.
There are several points of concerns showing on your screenshot.
Both voltages look low: Normally, “IG Power Source Voltage” would be higher than 12.3 volts. “+B Power Source” voltage usually will be a little different to the “IG” voltage but no way should it be so low at only 3 volts. Very strange results. Need to be sure about battery condition and that earthing is in good shape around the vehicle and that the engine was running at the moment the screenshot was taken. The “Oil Temperature Sensor” refers to the AHC Fluid temperature and shows as -22 degrees. This means either that the temperature sensors is disconnected or the engine is not running.
The “Steering Angle is a bit off-zero but worry about that much later, not now.
Then looking at the Height Control Sensor readings:
-0.0 inch Front Right (FR) Height Control Sensor reading
-1.3 inch Front Left (FL) Height Control Sensor reading
-0.2 inch Rear (RR) Height Control Sensor reading
Time for a long-winded explanation about these widely misunderstood readings ….
Large
differences in Sensor readings (FR to FL and FL to RR in this case) mean that the ECU cannot resolve the very different and conflicting voltage signals being received from the Sensors. In such a case, the ECU cannot determine which Sensor is correct. The AHC system then is unable to set the vehicle height automatically, so AHC cannot work. Height Sensor position also is one of the inputs on which TEMS depends. Conflicting signals prevent TEMS from regulating adaptive damping. In these circumstances, the ECU will put the AHC/TEMS system into ‘fail safe’ mode.
What does ‘fail safe’ mode mean?
There are several such modes mentioned in the FSM.
For the ‘fail safe’ mode relevant to the Height Control Sensor circuits, returning to description in the FSM “DIAGNOSTICS” section for DTC’s C1711, C1712, C1713 at Page DI-224:
“If trouble occurs in the height control sensor circuit, the height control is prohibited after the ECU has adjusted the height to the standard (fluid pressure correspond to the standard height)”.
The Japanese-to-English translation is not perfect! It means that in this mode, the ECU cannot resolve the conflicting signals, and that the AHC part of system is stopped after the vehicle has been returned to “N” height or at a height corresponding to the correct pressures at “N” height. The TEMS part of the system also is stopped and locked at damping mid-range, Step 8 of 16 Steps, and there is no active damping.
Unhelpfully, the FSM does not mention that the
ONLY time DTC’s C1711, C1712, C1713 will be recorded by the ECU and seen on Techstream is when the signal sent by the Sensor is
outside the specified voltage range under the heading “DTC Detecting Condition”. (As further background, the diagrams at Page DI-227, show the approximate actual voltage signals for “LO”, “N” and “HI” height settings which are within the range required by the ECU).
You have new Sensors, so how can there be a problem?
A DTC is not registered if a signal is within the required voltage range but is an incorrect voltage for the actual height of the vehicle. This can occur when
- the vehicle is not correctly cross-levelled and there are different heights side-to-side, or,
- the Sensors are worn or damaged (this can happen and not be visible), or,
- resistance due to poor connections at the Sensor or Harness reduce the voltage received by the ECU, or,
- one or more Sensors are incorrectly adjusted.
With or without a DTC, if there are conflicting signals received by the ECU from the Height Control Sensors, then the ECU will put the AHC/TEMS into 'fail safe' mode.
Reading the symptoms described while on the other side of the world and without seeing the vehicle means that it is a bit difficult to be sure – but I think your vehicle is in ‘fail safe’ mode. That is a reasonable diagnosis which fits the descriptions you have given.
You can test this by driving the vehicle (or have someone else drive) with Techstream connected and observe “Front Wheel Step” and “Rear Wheel Step” while the vehicle is in motion. If these remain at Damping Step 8 (of 16 Steps) while the vehicle is moving, that means that the active damping of TEMS is not working. That would support ‘fail safe’ mode. (It is normal to be at Step 8 when the vehicle is stationary).
What should be done next?
- Cross-level front of the vehicle using torsion bar adjusters,
- Decide whether to test the Height Control Sensors, Connectors and Harnesses electrically per FSM “DIAGNOSTICS” section, even though Sensors are new – if satisfied with condition, continue as below:
- Use “Height Control Operation Test” (also called “Active Test”) as described at Page 6 of the second attachment (or some other means) to raise/lower the hub-to-fender heights to those desired (IH8MUD recommendation: Front 19.75 inches, Rear 20.5 inches) then switch OFF the engine,
- With engine OFF but with Techstream connected and ONLY ignition ON, adjust all of the Height Control Sensors to read zero +/- 0.2 inches, with minimum possible difference between Sensors to release ‘fail safe’ mode. (At the Front Sensors the slider adjuster or the heim bolt can be used – but be aware that manipulating the heim bolt can be very fiddly. The Rear Sensor can be adjusted only by using the slider adjuster),
- Test vehicle and AHC and TEMS operation, check for DTC’s via Techstream
- When heights are correct, adjust AHC pressures using torsion bar adjusters at front, replacement springs if necessary at rear,
- When AHC pressures are correct, check difference in graduations at AHC tank when height setting is at “LO” and at “HI”. A difference of14 graduations means ‘globes’ are near new; when the difference has fallen to 7 graduations, replace the ‘globes’. Note: AHC pressures tell nothing about ‘globe’ condition.
AGAIN BROADCASTING THE GOLDEN RULE: ALWAYS HAVE JACKSTANDS UNDER THE CHASSIS RAILS WHEN WORKING UNDER THE CAR ON THE AHC SYSTEM – and yes, this is shouted in bold capitals not to be offensive but for good reasons, cannot be repeated often enough. Accidents do happen. A hard barrier -- such as fixed, lockable stands secure at the chassis rails, certainly not jacks -- is a ‘must have’ to ensure that an unexpected to descent of the car body onto a human body is impossible.
