Failed 16-step damper test (1 Viewer)

[LGU62]

I've been trying to figure out what's causing the rough ride on my 99 lx470 with ahc using the FSM troubleshooting section and the threads I've found here on MUD. Basic info-

Heights : LF-19.25 in, RF-19.5 in, RR-20.75 in, LR-20.25
Pressures : Front-6.8 MPa, Rear-6.6MPa (High, but still in spec)
14 graduations from L to N (Brand new spheres)

The ahc has passed all the tests in the troubleshooting section except the 16 step test. On step 1 all corners are very soft except the RR corner which is firm. Steps 2-8 the other three corners gradually increase in firmness but RR stays the same. Steps 9-16 all four corners increase in firmness and feel the same. I tested the resistance on the RR damping force control actuator per FSM and all are in spec. I also tested continuity of the wiring harness between the ahc ecu and the corresponding terminals on the RR actuator as well as between the actuator ground terminal and body ground. Everything checks out ok. Could the actuator still be bad even though the resistance readings are in spec? The shock absorber seems to be okay (no fluid leakage, raises and lowers fine). My next thought would be a bad ecu but when I drive with techstream hooked up it shows the step values changing and such which would lead me to believe the ecu is working. Is there anything I'm misssing that may be causing this? I'd rather not just start throwing parts at it because $$$.

 

[suprarx7nut]

If the corner behaves normally in the stiffer settings, but has no response in the softer settings I'm leaning towards the actuator. You can get one new for ~$350 or used for almost nothing. Tricky part is finding a used one before the current owner trashes them.

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I've never seen someone with that sort of partial response, but I'm looking at the shock or actuator. Both pretty unusual failures.

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**I'm in talks with someone on facebook with a full set of AHC stuff that I requested he ship to me (at my expense). If I can make that happen shortly, I'd be happy to test them all and see if I can ID any behavior by applying voltages. If so, maybe we can come up with a test routine. I can also help get the part sent your way if that's helpful.

 

[IndroCruise]

I've been trying to figure out what's causing the rough ride on my 99 lx470 with ahc using the FSM troubleshooting section and the threads I've found here on MUD. Basic info-

Heights : LF-19.25 in, RF-19.5 in, RR-20.75 in, LR-20.25
Pressures : Front-6.8 MPa, Rear-6.6MPa (High, but still in spec)
14 graduations from L to N (Brand new spheres)

The ahc has passed all the tests in the troubleshooting section except the 16 step test. On step 1 all corners are very soft except the RR corner which is firm. Steps 2-8 the other three corners gradually increase in firmness but RR stays the same. Steps 9-16 all four corners increase in firmness and feel the same. I tested the resistance on the RR damping force control actuator per FSM and all are in spec. I also tested continuity of the wiring harness between the ahc ecu and the corresponding terminals on the RR actuator as well as between the actuator ground terminal and body ground. Everything checks out ok. Could the actuator still be bad even though the resistance readings are in spec? The shock absorber seems to be okay (no fluid leakage, raises and lowers fine). My next thought would be a bad ecu but when I drive with techstream hooked up it shows the step values changing and such which would lead me to believe the ecu is working. Is there anything I'm misssing that may be causing this? I'd rather not just start throwing parts at it because $$$.

This is not a problem I have experienced but the described symptoms do raise suspicions about the RR Damping Force Control Actuator. You may find some common ground by having a look at the discussion about these Actuators in the thread at the link below, if only to share the frustrations described by @cruiser03 back in 2014, in his exchanges with @PADDO and @uHu and others:

AHC does large accumulator affect damping? - https://forum.ih8mud.com/threads/ahc-does-large-accumulator-affect-damping.793110/

It may be helpful to try the variation of the test described at Post #8 at this link in which you jumper Ts and E1 of the DLC1 to get into diagnostic mode, start the vehicle, then press the brake pedal one time to get into Actuator step 1, then drive the vehicle around a chosen course, progressively and briefly pressing the brake pedal to move up through the 16 steps, noting when/if the damping and ride is consistent with each Step and with the settings of the “Comfort” switch on the centre console. Step 1 is softest damping, Step 16 is hardest damping.

The signals sent by the ECU to the Actuators can be observed in real time by observing "Front Wheel Step" and "Rear Wheel Step" and “Damping Force Switch 1” and “Damping Force Switch 2” on the Techstream read-out (best if someone else is driving for safety).

However, this effort only gives some assurance that the ECU is sending the expected signals to the four Actuators, but does not tell anything about what is actually happening down at each individual Actuator.

Within each of the four Actuators there is a “Soft Damping Force Valve” and “Hard Damping Force Valve”, so it is possible to imagine differences between Step Range 1 to 8, and, Step Range 9 to 16 -- caused if one valve but not the other is stuck or is wholly or partially blocked – noting that there are a lot of tiny passageways inside the Actuators. Unless the circuits or solenoids are damaged, a valve being stuck or a passageway being blocked may not show in testing nor as a DTC.

You will have seen the FSM-specified diagnostic testing for C1721 and C1723 and you have indicated that the Actuators are electrically healthy and no Actuator-related DTC’s have been reported. This suggests that an Actuator mechanical fault or blockage maybe the problem. Note that defective seals in the AHC Height Control Accumulator have been reported as a source of detritus and blockage in the AHC/TEMS systems in older LC100/LX470 model years – see attachment.

If not seen previously, visualising the Actuator components may be helped by viewing the diagrams in the AHC/TEMS General Description found at
https://lc100e.github.io/manual/ , then tabs
New Car Features > CHASSIS > Suspension > Active Height Control Suspension and Skyhook TEMS

Ultimately, the expedient course of action may be to replace the RR Damping Force Control Actuator with a used part known to be in working condition.

While it does not seem to relate to the description in your Post #1, when chasing down causes of ‘rough ride’, it always is worthwhile to be sure that all three Height Control Sensors are in good condition by internal physical inspection and electrical testing per FSM – and that these Sensors are correctly adjusted – all so that there is no chance of a Sensor-related ‘fail safe mode’ disabling the TEMS adaptive damping and AHC. This 'fail safe mode' may not be accompanied by a DTC and is a frequent cause of 'rough ride'.

 

[informationjunky]

Probably a long shot.... do you have tech stream by chance?
I have a LS430 that began riding like a 70's Chrysler with springs and no shocks. When I hit a bump, it would bounce up and down for a while. I assumed I needed new air struts and have purchased replacements which I havn't installed yet. Last week I had a height sensor go out which caused my rear to default to highest setting. I replaced sensor and started playing around in tech stream to adjust heights. While in the adjustments, I stumbled across a "firmness" setting for each strut. My car now rides like it use to.

 

[LGU62]

Thanks for the replys and all the great info guys! After reading your posts I'm feeling a little more confident that the problem may lie with the RR actuator. A mechanical problem with the "Soft Damping Force Valve" certainly seems to fit the symptoms I am having. I took a drive with actuators set on step 1, then on step 8, and finally on step 16 as IndroCruise suggested. I could definitely feel the difference between the 3. Even with the actuators on step 1 there was some harshness ( I'm guessing from the RR although it was hard to pinpoint). when I got back to the house I ran through the 16 step test again with the same results. It would be nice if there were a way to test the mechanical operation of the actuators. If you make any progress on that suprarx7nut please let me know! No hurry though. I haven't really paid much attention to the height sensors as it seems to raise and lower just fine but it would probably be a good idea to test them. Techstream did show one of the front height sensors at .1 inch while the other front was -.5 inch and rear was -.3 inch. Would this be a big enough difference to cause it to go into fail safe mode? If it goes into fail safe mode would techstream show the ecu cycling through different steps? Every time I've driven with techstream hooked up it shows it cycling through steps. Thanks again for the help.

 

[IndroCruise]

Thanks for the replys and all the great info guys! After reading your posts I'm feeling a little more confident that the problem may lie with the RR actuator. A mechanical problem with the "Soft Damping Force Valve" certainly seems to fit the symptoms I am having. I took a drive with actuators set on step 1, then on step 8, and finally on step 16 as IndroCruise suggested. I could definitely feel the difference between the 3. Even with the actuators on step 1 there was some harshness ( I'm guessing from the RR although it was hard to pinpoint). when I got back to the house I ran through the 16 step test again with the same results. It would be nice if there were a way to test the mechanical operation of the actuators. If you make any progress on that suprarx7nut please let me know! No hurry though. I haven't really paid much attention to the height sensors as it seems to raise and lower just fine but it would probably be a good idea to test them. Techstream did show one of the front height sensors at .1 inch while the other front was -.5 inch and rear was -.3 inch. Would this be a big enough difference to cause it to go into fail safe mode? If it goes into fail safe mode would techstream show the ecu cycling through different steps? Every time I've driven with techstream hooked up it shows it cycling through steps. Thanks again for the help.

Not necessarily relevant to your original post #1 – but here is a bit more background information on the Height Control Sensors ….

The FSM suggests a tolerance of +/- 5 millimetres or +/- 0.2 inches on the Height Sensor readings – the explanation is less than clear but it means “close to zero, +/- 0.2 inches” on the handheld read-out. At page SA-313 of the first attachment an example is given of the Sensor readings on the handheld tester (meaning Techstream or similar) with the vehicle at stock Front and Rear heights from the factory and with “N” height selected at the centre console.

Later at page SA-315 the same attachment, the target voltage at “N” height at the actual Sensors is shown as 2.25 volts (+/- 0.08 volts at the Front Sensors) and also 2.25 volts (+/- 0.07 volts at the Rear Sensor).

Note that the AHC system is designed to self-adjust heights at the “N” height setting until the AHC Electronic Control Unit (ECU) receives a signal at or close to 2.25 volts from all the Height Control Sensors (after averaging the readings from the two Front Sensors).

So we can see that at “N” height at the Front, the read-out tolerance of +/- 0.2 inches corresponds to a voltage tolerance of +/- 0.08 volts or about 3.6% (of 2.25 volts) at the actual Sensor. You have reported a maximum difference between Sensor readings of 0.4 inches. We can assume that the relationship is linear and this might translate as a difference of 0.16 volts or about 7% (of 2.25 volts) in the signals being sent by the Sensors to the ECU.

Note that ECU sees nothing, knows nothing, about any physical condition around the vehicle. The ECU relies completely on the voltage signals input to it by the various Sensors. Obviously, the Sensors need to be in a healthy condition with their set points and conditions correctly adjusted. Otherwise, the ECU will receive incorrect or conflicting inputs which it cannot resolve. When this happens, the ECU is programmed to put the AHC and TEMS systems into ‘fail safe mode’ until adjustments are made which eliminate the error or the conflict.

You have reported that “Techstream did show one of the front height sensors at .1 inch while the other front was -.5 inch and rear was -.3 inch”. When translated into voltages, would these differences be big enough to cause the ECU to put the system into fail safe mode? I don’t know but I don’t think so. As you have already perceived, if the ECU had adopted a ‘fail safe mode’ caused by conflicting signals from the Height Control Sensors, then with Techstream connected you would expect to see "Front Wheel Step" and "Rear Wheel Step" both stuck at Step 8 on the read-out when driving, that is, unchanged from their position when the vehicle is stationary. You could try some very fine adjustment of the Height Control Sensor positions if you wish to bring the Techstream Sensor readings in inches (or millimetres) closer to zero and within tolerance -- but this might be ‘pursuit of perfection’ without any real benefit.

Nevertheless, may I suggest ongoing scepticism about Height Control Sensor condition. The presence of a Height Control Sensor DTC indicates a certain fault. However, the absence of a Height Control Sensor DTC provides no assurance that the Sensor is healthy.

Why is this?

As can be seen at page DI-227 of the second attachment, the ECU expects to receive signals from the Height Control Sensors swinging in the approximate range 0.45 volts to 4.05 volts. The Height Control Sensors (and the external connectors and harnesses) live in a hostile environment under the vehicle and are subject to heat, cold, sand, sticks, stones, mud, water, snow, salt, etc, etc, etc. Eventually, parts will corrode or deteriorate, or wear out in vehicles which are now 14 to 22 years old. Or the internal carbon trace simply may become electrically ‘scratchy’ in the high-wear area around the “N” height position, even if deterioration is not visible. A worn or decrepit Sensor easily can send a signal in the ECU-recognised range of 0.45 volts to 4.05 volts but it is no longer the correct voltage corresponding to the relevant height. In such cases there may not be a DTC (because the circuit is still intact and operating) but there may be conflicts between the signals from different Sensors, resulting in aberrant behaviour of the AHC/TEMS system with possible ‘fail safe mode’ and poor ride quality. Physical inspection and electrical testing per FSM is essential whenever Height Control Sensors are under suspicion.

Anyway, apologies – this sermon has now gone way beyond the scope of your original post in this thread concerning Damping Force Control Actuators!!

 

[LGU62]

No need to apologize! Preach on brother! Seriously, thanks for the great info. Sounds like it would be worth the time to pull the height sensors, clean, inspect, and test per the fsm just in case. A good project for this weekend. After that I think I’ll go ahead and replace the actuator as this seems to be the most likely culprit. May be a little bit though because I have a windshield that needs replacing too. I’ll make sure to report back when I get it done.

 

[LGU62]

Finally got around to replacing the actuator and still no luck. I still have a harsh ride and the RR corner still behaves the same during the 16 step test. I don’t really know what else it could be but the shock. The FSM says if everything else checks out and there is still a harsh ride to replace the shock. I guess I’ll try this as a last resort.

 

[mistersiumai]

Finally got around to replacing the actuator and still no luck. I still have a harsh ride and the RR corner still behaves the same during the 16 step test. I don’t really know what else it could be but the shock. The FSM says if everything else checks out and there is still a harsh ride to replace the shock. I guess I’ll try this as a last resort.

I have a 98’ 100 series

Newly replaced gloves and pumps. Numbers on the leveling sensors and pressures on the globes are correct. My problem now are the force damping switches. The seem to be OFF. I can feel every bump on the road (similar to driving an FJ 40). Comfort and Sport damping selectors don’t seem to work. I tried to do a suggestion which was to clean the contact point of the switches but still acquire the same result.

What could be the cause and possible remedy to it?

 

[lxguy]

Finally got around to replacing the actuator and still no luck. I still have a harsh ride and the RR corner still behaves the same during the 16 step test. I don’t really know what else it could be but the shock. The FSM says if everything else checks out and there is still a harsh ride to replace the shock. I guess I’ll try this as a last resort.

Hi @LGU62 ! How it ended? Did you fixed it yet?