AHC rear sensor

[scanderson76]

Feeling a little defeated. I removed my rear sensor to take a look as I was continuing to get a low reading in the rear. Adjusted it a couple times to get the rear in spec and it wasn't working, so I removed it and took it apart. Cleaned it up and everything looked good. Reinstalled and got this.

Rear is really high but Techstream is showing just slightly low in N. The picture certainly tells a different story.

Any assistance would be helpful. I went from halfway decent to a $hitshow. Fyi, I already ordered a new sensor, but any insight would be helpful. Thanks all.

 

[LndXrsr]

When you remounted the sensor, I assume you put it back at the same spot in the adjustment slider? I'd play around moving it up and down a bit and see if things normalize. But most likely just need a new sensor despite the innards looking okay.

 

[medtro]

Rear is really high but Techstream is showing just slightly low in N. The picture certainly tells a different story.

With the key at ON, adjust the rear sensor down until -0.6 becomes 0.0 or close to 0.0. Fine tune more if needed.

 

[scanderson76]

When you remounted the sensor, I assume you put it back at the same spot in the adjustment slider? I'd play around moving it up and down a bit and see if things normalize. But most likely just need a new sensor despite the innards looking okay.

Yes, I marked the spot before I removed it.

 

[scanderson76]

With the key at ON, adjust the rear sensor down until -0.6 becomes 0.0 or close to 0.0. Fine tune more if needed.

I doubt that will do a thing when it is off over 2.5in. I messed with it after getting myself into this predicament. Thanks for chiming in. I think there is more going on here.

 

[suprarx7nut]

We've chatted, but to add further input now, I'm pretty sure you've just got a dead sensor. Those sensors are just like throttle position sensor a, pedal sensors, etc... You can't always see the fault in the carbon track, but the common symptom is improper or varying readouts. I think that's what you've got going on here.

If you want to get it back to level you could move the arm mount up or down until you get ~ 21" wheel center to fender. It might need to be somewhere other than where it was. It's a fool's errand though, imo. If the sensor is bad, that's not a battle you can win. Just wait for the new sensor.

 

[LXKevin]

After you change the sensor get those pressures in spec

 

[medtro]

Feeling a little defeated. I removed my rear sensor to take a look as I was continuing to get a low reading in the rear.

What do you mean by low reading in the rear?

 

[scanderson76]

After you change the sensor get those pressures in spec

Thanks Kevin, the pressures were in spec before this calamity. With the rear sitting so high its throwing everything else off.

 

[IndroCruise]

Feeling a little defeated. I removed my rear sensor to take a look as I was continuing to get a low reading in the rear. Adjusted it a couple times to get the rear in spec and it wasn't working, so I removed it and took it apart. Cleaned it up and everything looked good. Reinstalled and got this.

Frustrating!!

Agree with @suprarx7nut and @LndXrsr. Cleaning the sensor is a good start but it may not do the trick. It is still possible that unseen imperfections in the carbon track will result in 'scratchy', inconsistent voltage signals to the ECU.

You could try adjusting by sliding the sensor adjuster to achieve a zero reading as mentioned by @medtro – key “ON”, Engine “OFF” so that the AHC system does not start and cause the body to move up or down during adjustment, Techstream connected maybe with a long lead and laptop with you under car if you want to see the Sensor readings in real time. Easier if using a scanner with Bluetooth connection to ECU.

BROADCASTING AGAIN 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 is a ‘must have’ to ensure that an unexpected descent of the car body onto a human body is impossible, not just unlikely.

You also could try testing the Sensor electrically per FSM extract attached at Page DI-227 [always a good idea when Sensors are taken off for cleaning before re-fitting to see that the voltage output changes smoothly in a linear fashion -- no flat spots, no jumps] as the sensor arm is moved through its arc and that the voltages are as shown in the FSM extract with the arm approximately at the designated positions for “LO” and “N” and “HI”. Or at least check that resistance changes smoothly through the swing of the Sensor arm.

Bottom line: Your previous posts suggest that the vehicle is ’06 LX470 – so 15 years old, same vintage as my ’06 LC100 which lives on a relatively dry continent. All three Sensors are likely to be past their best. Perversely, the act of cleaning the Sensor may even have been enough to cause the final disruption. A new Sensor is recommended as the reliability of existing Sensors is questionable at this age and replacement is inevitable sooner than later.

It is also important to check the voltage available at the connector (with key “ON”, engine “OFF”), and also to check continuity of the Sensor connector back to the ECU or at least back to the next connector in the harness (with key “OFF”, engine “OFF”). Connector problems are not uncommon and harness problems also can occur especially in exposed locations.

By the way, the additional rear height accounts for the high rear AHC pressure but the Height Control Accumulator pressure is unusually low at 9.1 Mpa (expect ~10.5 Mpa). Hopefully, this may mean only that the measurement was taken a bit too quickly and the AHC Pump had not finished recharging the Height Control Accumulator – best to allow ~30 seconds after arriving at “N” height before pressure readings. It also may mean that the now-inconsistent Sensor voltages have caused the ECU to put the AHC/TEMS system into ‘fail safe mode’. This 'fail safe mode' will clear when the fault(s) is/are cleared. There could be more than one problem. The Front Sensors may not be innocent.

Also be aware that Sensor problems do not always throw a DTC visible on Techstream or other scanner – be guided by the observed symptoms.

 

[scanderson76]

Follow up, replaced the sensor and we are all good in the hood! Everything back in spec and pleased as punch. Thanks for all the help!

 

[Mumblix]

Follow up, replaced the sensor and we are all good in the hood! Everything back in spec and pleased as punch. Thanks for all the help!

Good to know that replacing the sensor fixed your problem. Mine started doing the exact same thing yesterday. I've got a sensor on order. The poor rig looks and drives funky with its butt up in the air.

 

[AtoyotA]

We've chatted, but to add further input now, I'm pretty sure you've just got a dead sensor. Those sensors are just like throttle position sensor a, pedal sensors, etc... You can't always see the fault in the carbon track, but the common symptom is improper or varying readouts. I think that's what you've got going on here.

If you want to get it back to level you could move the arm mount up or down until you get ~ 21" wheel center to fender. It might need to be somewhere other than where it was. It's a fool's errand though, imo. If the sensor is bad, that's not a battle you can win. Just wait for the new sensor.

@suprarx7nut does this same answer apply here? i replaced my rear height sensor with OEM and when i took apart the old one, I expected to see corrosion or at least some dirt, but it looked super clean.

 

[suprarx7nut]

@suprarx7nut does this same answer apply here? i replaced my rear height sensor with OEM and when i took apart the old one, I expected to see corrosion or at least some dirt, but it looked super clean.

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That looks pretty clean, but this isn't a visual inspection kinda deal. The sensor can have faults in the traces or the arms that are tough to spot purely based on visual inspection. You'd need to hook it up to a logging device and move the sensor around to see if the response is stable.

Something like this would probably do what you need: https://www.digikey.com/en/products...jUF1K00Lbk1qaw1XNlnOAWo8toCmwIYAaAj9_EALw_wcB

Hooking it up to a normal voltmeter might help show an obviously bad sensor, but those are generally really slow to react and only show a measurement every second or so. I'm not sure what the AHC ECU needs as far as stability, but I'm sure it's sampling that sensor many times per second. My guess is 100-1000 times per second.

If you're not well versed in electrical testing or really into the concept as a hobby then I think you just need to try a new sensor. All it takes is a microscopic crack in the trace and the sensor is worthless.

 

[IndroCruise]

As mentioned by @suprarx7nut, internal visual inspection of a Height Control Sensor may give a few clues, especially if corrosion or other degradation is obvious, but visual inspection alone provides no assurance that all is good electrically, even if the internals look good. Testing is essential.

A version of the FSM method of Height Control Sensor testing is not as good as the more modern method suggested by @suprarx7nut -- because in rotating the Sensor in an effort to observe by eye that voltage changes smoothly as the tiny brushes move over the carbon path, a break or poor contact may not necessarily be registered quickly enough by the voltmeter before the brush moves to a new position. Testing for the FSM-specified voltages at the Sensor positions for LO, N and HI may be helpful but may not reveal what is happening between those positions.

There is an alternative method mentioned long ago by @PADDO -- this resistance method easier to do but it also relies on the speed of response of the meter. See Post #2 at:

High as a kite, hard as a rock! (Yes AHC again...)

Hi guys! I have a 2001 VX100 1HD-FT diesel with 300,000 miles on it. I've owned it for two years and love the comforts over the HJ61 it replaced. But the AHC is acting up! I don't want to go conventional, I want to keep the AHC. AFAIK everything except height sensors are original, and I know...

forum.ih8mud.com

It does not hurt to try these methods -- just be wary of the limitations.

Also be aware that provided that the Height Control Sensor is sending a signal to the ECU in the range 0.3 volts to 4.7 volts (within the FSM time limits -- see extract below), then the ECU will read this as a healthy signal and no Diagnostic Trouble Code (DTC) will be recorded, EVEN IF, due to a fault, the Sensor arm is in the wrong position for the voltage output. The ECU sees only the voltage signal. It has no idea of the position of the Sensor arm, nor the position of the internal tiny brushes, nor the actual height of the vehicle. For this reason, a DTC can be accepted as a definite fault -- such as a short circuit or an open circuit -- but the absence of a DTC provides no assurance that all is good within the Height Control Sensor. Observation and interpretation of vehicle behaviour also is required -- such as the vehicle settling too high or too low for the selected height, LO, N or HI.

For all of that, the main point is that Height Control Sensors are 'wear items' which are in motion whenever the vehicle is in motion. They also are located in a hostile environment. If Height Control Sensors are original on vehicles which are now 16 to 25 years of age, then replacement before failure is simply prudent preventative maintenance, especially if vehicle reliability is important.

All of that said, suggest also be wary of faults in connectors and harnesses. Faults in a connector or a harness will result in the same symptoms as a fault within the Sensor itself.

 

[AtoyotA]

i installed the new OEM sensor and was looking for justification for the $$ spent (considering how clean the inside of the old sensor looked) and both of you definitely gave me that justification - so thank yall for that!