Ahc acting up (1 Viewer)

[swoop]

Hey all, my ahc has been acting a bit different recently. The car when parked constantly makes small adjustments up and down. Raises probably a quarter inch, then lowers a quarter inch and does this repeatedly until I resume driving. It’s hard to say if it’s doing the same thing as a drive, but it’s definitely noticeable when parked. I’ve also noticed it seems to take longer to raise and lower when pushed into high or low setting.
The backstory here is worth mentioning I believe. I had the vehicle at a lexis dealership and asked that they let me know neutral pressure specs so I could determine if a new set of rear springs/spacer might be needed. When I picked the car up it wouldnt raise or lower at all, and ahc lights ready off. I sent it back to the dealership and let them know what was happening. They came back and let me know that the rear height sensor was oddly enough, failed. After the insane quote I got to replace it, I got them to agree to cover labor, and I supplied them with a doorman version of the height sensor. They installed, and things functioned, but didn’t seem to raise and lower the vehicle with anywhere need the speed it used to (guessing they pushed the pump to its last leg during the install by raising and lowering the vehicle repeatedly).
Now the vehicle is doing these constant small adjustments when sitting still(even on level ground), where as it used to make a large adjustment all at once say when I was parked on a hill. Could that be a sign of a bad pump? Or potentially failing front height sensors?
Thanks in advance.

 

[swoop]

Any thoughts here?

 

[l3n0x]

Probably a hight sensor is getting tired. They do wear out over time. Best would be to hook up techstream and check which sensor reading is jumping around.

 

[nbailz]

Probably a hight sensor is getting tired. They do wear out over time. Best would be to hook up techstream and check which sensor reading is jumping around.

Along those lines, maybe the Dorman isn't a good replacement? I replaced my rear height sensor with an Aisin HST - 026 without any issue.

 

[swoop]

I’ve seen the Dorman recommended here many times in the past and have never heard of issues. Have you heard of similar problems out of a doorman unit?

 

[nbailz]

I’ve seen the Dorman recommended here many times in the past and have never heard of issues. Have you heard of similar problems out of a doorman unit?

Nope, haven't heard of any problems assuming it was installed correctly.

 

[ramangain]

Take a look-see with Techstream. The $tealership may have made adjustments and naturally not taken notes or told you.

Correct the assumptions below if they are not true:

1. Fluid in reservoir has a few graduations left when in H and accumulator has filled
2. The system has been properly bled (when you crack the nipples at each globe and accumulator, you may get a very slight fizz at first but then just fluid)
3. None of the supporting bracketry or lever arms for the height sensors appears bent, even just a bit

If these assumptions are correct, let's hope Techstream has some answers for you.

 

[PADDO]

I’ve seen the Dorman recommended here many times in the past and have never heard of issues. Have you heard of similar problems out of a doorman unit?

It’s actually pretty easy to screw up swapping in a Dorman aftermarket sensor if you’re not just a little bit careful. They can be inadvertently over rotated when tightening the retainer nut and you loose the crucial mechanical to electrical (resistive) alignment and consequently get bad and/or random error position feedback. I used to recommend them as a low cost alternative to the Aisins but haven’t for ages. I’ve written a few posts a while back that should come up in search about the importance of ensuring the lever arm is properly seated on the potentiometer’s stub shaft before tightening the nut to avoid over rotations and ruining the supposedly new and good sensor when doing the swap.

 

[LndXrsr]

Not sure if they were Dorman or another random amazon knockoff, but plenty of folks have popped brand new sensors in after confirming a bad sensor and developed new issues dues to a cheap/faulty sensor or error during installation. The timing of your problem and the part being installed are too coincidental to ignore.

 

[swoop]

It’s actually pretty easy to screw up swapping in a Dorman aftermarket sensor if you’re not just a little bit careful. They can be inadvertently over rotated when tightening the retainer nut and you loose the crucial mechanical to electrical (resistive) alignment and consequently get bad and/or random error position feedback. I used to recommend them as a low cost alternative to the Aisins but haven’t for ages. I’ve written a few posts a while back that should come up in search about the importance of ensuring the lever arm is properly seated on the potentiometer’s stub shaft before tightening the nut to avoid over rotations and ruining the supposedly new and good sensor when doing the swap.

Not sure if they were Dorman or another random amazon knockoff, but plenty of folks have popped brand new sensors in after confirming a bad sensor and developed new issues dues to a cheap/faulty sensor or error during installation. The timing of your problem and the part being installed are too coincidental to ignore.

dang I hate to hear that. Question though- do all 3 height sensors work in conjunction where it would be possible the dorman is causing issues with the front end? Seems like it’s the front sensors doing the frequent lifting/lowering vs the rear that was replaced with the dorman?

also, are you able to buy the aisin without the brackets ect and just the sensor? All I’ve found is the complete package.

 

[swoop]

@PADDO Any thoughts on if the front and rear sensors are “connected”? The single rear is the one that was replaced with a dorman unit, but the front is what’s acting erratically.

 

[PADDO]

@PADDO Any thoughts on if the front and rear sensors are “connected”? The single rear is the one that was replaced with a dorman unit, but the front is what’s acting erratically.

The three sensors share a common signal point to the ECU, the two front sensors are on their own circuit and provide a front left and front right input to the ECU. The rear is on its on cct and it provides it’s own input. Firmware determines vehicle heights and leveling on actual voltage feedback from the sensors - L has its voltage, as does N and H. In control systems the term for constant small corrections to get back to the ordered position, N in this case, is called hunting and it can be an electrical issue due to a poor quality feedback signal of hydraulic due to internal leakage or some other problems.

 

[swoop]

@PADDO

The three sensors share a common signal point to the ECU, the two front sensors are on their own circuit and provide a front left and front right input to the ECU. The rear is on its on cct and it provides it’s own input. Firmware determines vehicle heights and leveling on actual voltage feedback from the sensors - L has its voltage, as does N and H. In control systems the term for constant small corrections to get back to the ordered position, N in this case, is called hunting and it can be an electrical issue due to a poor quality feedback signal of hydraulic due to internal leakage or some other problems.

Thanks for that information that I will admit is a little over my head. Are you saying that the rear dorman sensor wouldn’t be causing issues with the front end “hunting” due to it being on its own circuit and that it’s most likely a hydraulic leak?

also, hunting I’m sure causes some additional wear on the pump being that it’s adjusting so frequently, but any other issues with driving the truck as is when it is “hunting”?

 

[PabloCruise]

Any thoughts here?

Some good, general AHC knowledge: Definitive list of AHC maintenance items

 

[PADDO]

@PADDO

Thanks for that information that I will admit is a little over my head. Are you saying that the rear dorman sensor wouldn’t be causing issues with the front end “hunting” due to it being on its own circuit and that it’s most likely a hydraulic leak?

also, hunting I’m sure causes some additional wear on the pump being that it’s adjusting so frequently, but any other issues with driving the truck as is when it is “hunting”?

The vast majority of undefined, random height/leveling issues are the result of some sort of sensor or harness defect - wear and tear, broken/maladjusted mechanisms, internal corrosion or a harness issue. Without monitoring the sensors feedback (all three) and generally assessing the system it’s not possible to diagnose 100%. But I bet it’s a bad sensor