AHC - Sudden Loss of Functionality - HELP

[LXstatic]

If a new potentiometer hasn't rectified the problem and DTCs won't manually clear (Tc&E1 jumped + brake pushes) then this really suggests a harness issue - DTC 1713 is "rear height control sensor circuit" open or short. The erratic and random height behavior you initially saw is/was indicative of a failing height sensor/mechanism but this won't necessarily throw a code until the system sees either a very low voltage , <0.3v ~ short, or > 4.7v ~ open circuit. If the sensor is in the process of dying through wear/corrosion then it usually provides bad feedback resulting in bad levelling control which is what you saw. Ideally you'd connect Techstream and with just IG on confirm that the sensors are responding to changes in chassis height, jack up/lower the rear and observe the feedback change to the ecu etc. At a minimum put a multimeter on the replacement sensor and confirm its function; about 3900 ohms iirc between pins 1-3, place the wiper at mid displacement and you should read about 1950 ohms 1-2 and 2-3; gently rotate the wiper shaft and observe the resistance changes from min to ~ 3900 ohms between 2-1 and 2-3 depending on which way you rotate the wiper shaft. If you can verify the replacement pot is fine then you'll need to get into harness and connector tracing looking for bad/loose/corroded connectors, chafed wiring, exhaust gas leak burn through and such.
You initially listed several other faults too - 1762 (very common fault that can probably be ignored if it doesn't continually set); 1763 (abnormal over pressure possibly due to solenoid valve failing to open - this is interesting); 1776 (speed sensor circuit - you've got the height sensor override? so not unexpected if the switch has been flicked whilst moving etc) and 1777 (steering signal? my 03 LX FSM doesn't list this as an AHC fault as such, it does come up as a GX fault though so not sure about this sucker). So where too? I'd try and start with a clean slate: clear faults; observe height sensor feedback; post a screen shot of the AHC ecu page up with all parameters; verify the 3 connectors at the ecu are seated properly and that the override wiring was done appropriately with good insulation on the splices and the switch; verify no other wires were inadvertently cut/badly reconnected etc; in Techstream I'd try operating the control valve and accumulator solenoids (you can also operate these manually by shorting Ts&E1 and configuring the height control switch modes); check/clean/reseat each connector.

OK, thanks so much for the feedback. I wlll give all this a look in the next couple of days. You rock!!

 

[patmeclark]

It is fairly simple, just remove the switch from the assembly and re-install. Make sure to mark the position of the top bolt of assembly in slot in order to put it back where it was, or take a picture of the position. Unless you want to go ahead and do an AHC lift while you're under there.

Thanks! PADDO mentioned in another post replacing the sensor then "dialing it in" in Techstream, and I wasn't sure exactly what that meant. It does make sense to me that the swap out would be pretty simple. I might do an AHC lift later on but for now I just need to get it working solid and make sure it's gonna stay that way. Hopefully new tires before too long, so I might do it then.

 

[LXstatic]

If a new potentiometer hasn't rectified the problem and DTCs won't manually clear (Tc&E1 jumped + brake pushes) then this really suggests a harness issue - DTC 1713 is "rear height control sensor circuit" open or short. The erratic and random height behavior you initially saw is/was indicative of a failing height sensor/mechanism but this won't necessarily throw a code until the system sees either a very low voltage , <0.3v ~ short, or > 4.7v ~ open circuit. If the sensor is in the process of dying through wear/corrosion then it usually provides bad feedback resulting in bad levelling control which is what you saw. Ideally you'd connect Techstream and with just IG on confirm that the sensors are responding to changes in chassis height, jack up/lower the rear and observe the feedback change to the ecu etc. At a minimum put a multimeter on the replacement sensor and confirm its function; about 3900 ohms iirc between pins 1-3, place the wiper at mid displacement and you should read about 1950 ohms 1-2 and 2-3; gently rotate the wiper shaft and observe the resistance changes from min to ~ 3900 ohms between 2-1 and 2-3 depending on which way you rotate the wiper shaft. If you can verify the replacement pot is fine then you'll need to get into harness and connector tracing looking for bad/loose/corroded connectors, chafed wiring, exhaust gas leak burn through and such.
You initially listed several other faults too - 1762 (very common fault that can probably be ignored if it doesn't continually set); 1763 (abnormal over pressure possibly due to solenoid valve failing to open - this is interesting); 1776 (speed sensor circuit - you've got the height sensor override? so not unexpected if the switch has been flicked whilst moving etc) and 1777 (steering signal? my 03 LX FSM doesn't list this as an AHC fault as such, it does come up as a GX fault though so not sure about this sucker). So where too? I'd try and start with a clean slate: clear faults; observe height sensor feedback; post a screen shot of the AHC ecu page up with all parameters; verify the 3 connectors at the ecu are seated properly and that the override wiring was done appropriately with good insulation on the splices and the switch; verify no other wires were inadvertently cut/badly reconnected etc; in Techstream I'd try operating the control valve and accumulator solenoids (you can also operate these manually by shorting Ts&E1 and configuring the height control switch modes); check/clean/reseat each connector.

On the Dorman and OEM sensors there is a definite slot below the threads of sensor that looks to be important for install. Is it possible that the "slot" is in the wrong position and hence causing the sensor to not read correctly? Is this what you mean by "Best to swap over off vehicle to ensure you seat their lever arms properly and don't accidentally rotate the potentiometers wiper beyond its stops." ?? I am afraid this may have happened when I swapped in the new one. If this is the case, did I kill the new unit or could I just put it back in the correct orientation? Thanks again for all your input!

 

[PADDO]

Both the OE and Dormans have a raised rectangular profile on their respective wiper stub shafts that mates with a corresponding rectangular recess in the lever arm - the profile and recess lock in the lever arm (with 10mm nut securing both together) to ensure the sensors' wiper moves in unison with chassis/UCA displacement so as to provide accurate, proportional height and wheel displacement feedback. Ensuring they are aligned and seated during swap over is very important. If the lever isn't seated properly on to the stub shaft raised profile then you run the real risk (from experience) of over rotating the wiper past its stops when you tighten the nut because the stub can turn freely with the nut if not restrained by the lever. Once over rotated the potentiometers resistance to actual angular displacement is buggered up and its at best going to be very unreliable if you can realign it to where it was at production. For example, the OE sensors when at N height, which closely corresponds to the little transport/handling pin being inserted in its housing, returns 2000 ohms across terminals 1-2 iirc and if you cranked the wiper stub you'd no longer have that resistance to angular position correlation and you get ridiculous feedback numbers. Unless the guts of the potentiometer were so over rotated to the point that you've created an open cct then it's probably not the root cause of your on going issue (DTC 1713). Easy to check if the potentiometer is ok, put a multimeter on it and check resistances, the wiper should be limited to about 175 degrees of angular rotation and if you guesstimate the middle point then you should read similar and balanced resistance values between terminals 1-2 and 2-3. This all sounds a bit long winded, it's really no harder than, say, ensuring a bayonet connection light bulb is seated properly when you change it.

 

[LXstatic]

Both the OE and Dormans have a raised rectangular profile on their respective wiper stub shafts that mates with a corresponding rectangular recess in the lever arm - the profile and recess lock in the lever arm (with 10mm nut securing both together) to ensure the sensors' wiper moves in unison with chassis/UCA displacement so as to provide accurate, proportional height and wheel displacement feedback. Ensuring they are aligned and seated during swap over is very important. If the lever isn't seated properly on to the stub shaft raised profile then you run the real risk (from experience) of over rotating the wiper past its stops when you tighten the nut because the stub can turn freely with the nut if not restrained by the lever. Once over rotated the potentiometers resistance to actual angular displacement is buggered up and its at best going to be very unreliable if you can realign it to where it was at production. For example, the OE sensors when at N height, which closely corresponds to the little transport/handling pin being inserted in its housing, returns 2000 ohms across terminals 1-2 iirc and if you cranked the wiper stub you'd no longer have that resistance to angular position correlation and you get ridiculous feedback numbers. Unless the guts of the potentiometer were so over rotated to the point that you've created an open cct then it's probably not the root cause of your on going issue (DTC 1713). Easy to check if the potentiometer is ok, put a multimeter on it and check resistances, the wiper should be limited to about 175 degrees of angular rotation and if you guesstimate the middle point then you should read similar and balanced resistance values between terminals 1-2 and 2-3. This all sounds a bit long winded, it's really no harder than, say, ensuring a bayonet connection light bulb is seated properly when you change it.

So, first and foremost, thanks @PADDO for your infinite wisdom in the AHC department! Secondly, I made a big blunder of replacing the sensor. I was in a huge hurry when I did it and did not seat the arm on the sensor properly, therefore the feedback was "throw a code and give a wonky stance". I reinstalled the sensor today on my lunch break away from all the hectic crap at home that got me into a hurry last weekend (pretty sad, huh?). Anyway, I got it all sorted and all the codes went away, I drove it around and all is good for now. Thanks to everyone else as well for all your inputs in the matter, much appreciated!!

 

[leej]

I've been running the Dorman sensor on the rear since late 2015 with NO problems.

Lee
2000 LC
2004 LX470

 

[fjryan]

I got in mine this morning and I get a high front end and some bounce. Having done a little reading on here, I'm thinking I might have a bad sensor and maybe a globe. Does anyone have a FSM for the LX? Mine's a '03 LX470. I have a 100 series Land Cruiser but it doesn't cover the AHC. Thanks in advance for help fellas!