LX470AHC troubles/update

[fish933]

Hi all,
I am still fighting to repair my AHC system on my 2000 LX470 and after a trip to my local Lexus dealer am convinced I need to fix it myself.

An explanation of the fault:
The AHC 'OFF' light is constantly blinking on the dash indicating a fault.
The vehicle has lowered itself to the lowest positon possible and is now undriveable as i don't think there is any fluid in the shocks.

Trouble codes:
I have taken the LX470 to Toyota and an independant mechanic to have their scanner connected. The Toyota scanner showed the following trouble codes:C1718 & c1762. The mechanics codes were C1751 - Continuous current to compressor and C1762 - Abnormal Oil pressure to pump.


Thinngs I have tested:

All height control sensor have been checked and are working correctly.
All AHC relays were tested and working correctly.
The Height Control Accumulator solenoid was tested by applying 5volts from an independant supply. I could here it click closed so assume it is OK.
The four solenoids in the Control valve assembley were checked by applying 5 volts. Althought this test was only guess work. I checked resistance between the pins and found a common pin which I assumed was the negative side of each solenoid. Again I could here the solenoids click. I would still like to see the correct pinout of the valve assembly to check it more accurately.

Connection between above sensors and Height Control Accumulator to the AHC ECU has been checked and is OK, as is connection of the pump pressure sensor and temp sensor to the ECU.
I have checked resistance between pins on the Damping Force Control Actuators (which the round gas filled spheres or chambers are attached to). The actuator consists of a 16 step DC stepper motor. The resistance between each pin was the same on all four actuators so I assume they are working OK. Tho I am not sure if these are 'normally open' or need power to allow fluid in and out of the shocks??

I have removed the AHC Pump and run it directly from the battery with a pressure gauge connected. The pressure rose to over 1500psi before stalling which I beleive would be enough to power the system. The pump motor only drew about 8 amps at this point which I also beleive to be OK.

Things I need to test and get more info on:
The pump pressure sensor. Does anyone know how it operates? It is a 3 wire sensor and in my vehicle is being feed 5 volts from the ECU and one side is connected to ground. I assume the other pin is the signal output which I further assume is a variable voltage output - different voltages for different pressures. Can anyone confirm the operation of this sensor? What should the voltage input be? Is it a variable voltage output or is it a milliamp output?
The pump working pressure: Does anyone know what pressure the hydraulic system should operate at? I have documents showing the sealed gas pressure of the Height control Accumulator is 853psi and would assume the 1500 psi I ran it to would be sufficient.

The Control Valve Assembly:
Does any one have the pin out for this assembly? I would like to find out which pin drives each of the leveling valves and gate valves.
The temperature sensor: The temp sensor is connected to the pump housing only and is not in direct contact with the hydraulic fluid. Does any have any info on this sensor?
The ECU: Does anyone know how to reset the ECU so I can reset it between tests?

That is about it for now. I have spent many many hours on this system and probably many more. My wife thinks I am obsessed but I think it's just a hobby - tho a frustrating one at times.

Sorry for the long rambling email. Any help would be appreciated.

Cheers
Fish933

 

[hkeller]

Are the accumulators flat? Sounds like the ride I had when mine went totally flat.

 

[uHu]

That's the most in-depth fault-finding I've heard about on the AHC system. Impressive.
From your Q's it sounds like you don't have the handbook or diagrams. (They are most helpful) If that's the case, I 'll see if I can dig out some useful pages.

What is the production date of your cruiser, before or after 08/2000?
There are changes in how the sensors work before and after this date.

1751 is a time-out - the reqested action did not take place within a time limit. System halted by ECU.
1762 is "Pump does not supply fluid"

Here are a few pages on reading and resetting DTC's. Other pages depend on pre or post Aug 2000. (Get yourself a signature line)

 

[fish933]

Hi hkeller, by accumulators I assume you mean the four Dampind Force Actuators - the round softball size bladders. These may be flat in my vehicle - I haven't tested them yet. But even if they were flat I would think that I could still raise and lower the vehicle. Were you still able to do this when yours went bad? Thanks

 

[fish933]

Thanks uHu,
Your pages are a very interesting read. i willtry some of the tests tomorrow. One question though what is the SST they talk about in the checks. I assume that I can just link the Tc & CG with a peice of wire???
My car is pre Aug 2000. Any pages you can dig up will be very useful. Thanks again.

 

[hkeller]

No, if the accumulators or actuators are flat, not sure which term is correct, but yes, the round, softball sized thingees, then you will not be able to raise or lower your vehicle. The symptoms you describe are classic symptoms of failed accumulators/actuators, which is the most likely part to fail in this system.

 

[fish933]

Very interesting hkeller. Will the AHC ECU pick up a problem with the Actuators? And will the ECU lock out if it does? The AHC 'Off' lamp on the dash is blinking constantly indicating a fault.

 

[uHu]

Recommend checking the pump and in particular the pressure sensor first. (if the DCT is correct) (se attached)

As far as I know, and have experienced, the AHC system knows nothing about faulty/flat spheres, and will adjust to Hi, Low and Normal regardless. (The spheres are often called accumulators, but there is another cylindrical container named accumulator. The spheres are screwed on to the actuators)
There is a test for measuring the state of the spheres, but you have to get the up/down action going first

Yes, the Tc or Ts can be shortened to CG with a piece of wire.
Because the plug is a bit difficult to get to, I attached three small wires to an on-off-on type toggle switch, and plugged the common(centre) into CG, and the two sides into Tc and Ts respectivelty. That way I can just flip the switch (before starting and pressing 5xDown) for the Active Test, or the other way for reading DTCs.

 

[uHu]

To til: (yes, that's norwegian)

 

[uHu]

btw:
I'd say the symptoms are classic Faulty Pump, but since you have checked the pump itself(?), maybe only the sensor is faulty. Could be a few other things tho. Seems like the DTCs are not too good on this system.

Have you bled the system well??

PS
And tell you wife that this obsession is better than most other obstinate, obstructive obsessions you could have.

 

[hkeller]

The rounds sphere are actually the damping for actuator accumulators. The other accumulator (the large cylinder in the driver's side frame rail) is the height control accumulator.

When my front damping for actuator accumulators went flat, I mean completely flat with no travel in the system whatsoever, the height control would not work and the off light flashed. Replacement of teh accumulators fixed this.

 

[hkeller]

Let me correct my last post. The OFF light on flashed when I pushed the AHC up botton.

 

[uHu]

The spheres are the gas springs. They have the same function as steel springs. Some cars have only gas springs, either spherical or cylindrical.
In the LC, when balanced with the correct hydraulic pressure, they actually lift your vehicle off the bump stops. Because of the hydraulic transfer of force from the wheel (via the hydraulic cylinder which look like a shock absorber) to the gas spring (sphere), it is easy to adjust the damping via the actuators. I.e: The damping happens in the actuator, and the sphere is just a spring (or a pressurized gas sphere with a membrane separating the gas from the hydraulic fluid).

 

[fish933]

uHu, Thanks for all the info. The pressure sensor is definitely faulty. It is being supplied 5 volts but the output is very low - less than 1v. I have also tested the sensor whilst the pump was removed from the vehicle. I pressured the pump up to 1500 psi and applied 5 volts to the sensor. The sensor output voltage did not change.
My next step is to replace the sensor but Toyota and Lexus do not stock the item so it could be a 6 week wait whilst it is shipped out from Japan. I would like to look into using a non-genuine sensor. There are many on the market but I am not sure of the parameters of the sensor. Do you have any information on the sensor? It is made by Denso in Japan.
Toyota part number is 89192-60010.
Denso part number: 499000
Other markings: 3B20-4400.
If I can find out the pressure rating of this sensor, pressure range for the AHC system and the expected voltage output at different pressures I could install an alternative sensor. Any info would be great- thanks.

 

[uHu]

Try a wrecker (or whatever you call those junk-yards for vehicles. Think there's a different term for US, UK and Aus).
Maybe there's cruiser in your neigborhood you could pray on

 

[Texasoil]

send me an email and I will send you all the pages from the REAL repair manual. Gives the voltages needed. Just needs to have high enough for the 'computer' to tell the pump is delivering.

 

[rahper7]

bro can you send me the AHC repair manual?

 

[rahper7]

bro can you send me the AHC repair manual?

bro can u plz send me the AHC repair manual? regards