Jim_Chow
V8_Fan
Are you referring to the "control valve" assembly? That's where the hydraulic line from the pump goes and splits to each of the wheels and the height control cylinder.
How to reset AHC pump or bleed air from the system?
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Are you referring to the "control valve" assembly? That's where the hydraulic line from the pump goes and splits to each of the wheels and the height control cylinder.
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Not exactly.
I got the EPC disks, so I can understand the schematic of the Hydraulic.
The pump indeed delivers to this control valve assembly ( same HP pipe from HP pump to control valve is used for hydraulic fluid back to reservoir; instead of one HP pipe and one LP return pipe). Which makes already this valve not ordinary!
Then the control valve splits to the four actuator/nitrogen globes on each wheel as well as to to the Heigth control cylinder which I called - could be confusing- the central control accumulator.
I figure out this Heigth control cylinder is not just a reserve for the AHC function , but also for the suspension ( avoid that the pump runs too often everytime the actuators do operate) by delivering volume/pressure accumulated, thru again the main control valve to each of the 4 actuators ,when requested by the ECU .
So I guess if lot of air is trapped , it could be in the Heigth control cylinder ( there is a bleeder on it, so no problem) or in the 4 actuator/globes.
So my logic will be to flush first (if I can) the control cylinder, then the actuators.
And ... I will not give up !!
I got the EPC disks, so I can understand the schematic of the Hydraulic.
The pump indeed delivers to this control valve assembly ( same HP pipe from HP pump to control valve is used for hydraulic fluid back to reservoir; instead of one HP pipe and one LP return pipe). Which makes already this valve not ordinary!
Then the control valve splits to the four actuator/nitrogen globes on each wheel as well as to to the Heigth control cylinder which I called - could be confusing- the central control accumulator.
I figure out this Heigth control cylinder is not just a reserve for the AHC function , but also for the suspension ( avoid that the pump runs too often everytime the actuators do operate) by delivering volume/pressure accumulated, thru again the main control valve to each of the 4 actuators ,when requested by the ECU .
So I guess if lot of air is trapped , it could be in the Heigth control cylinder ( there is a bleeder on it, so no problem) or in the 4 actuator/globes.
So my logic will be to flush first (if I can) the control cylinder, then the actuators.
And ... I will not give up !!
Jim_Chow
V8_Fan
FYI, I found the DTC62 (pump & motor do not supply fluid) trouble shooting procedure as outlined in the FSM, vol 1, pg. DI-379. You are supposed to trouble shoot in this order:
1. Check fluid level of resevoir tank. If NG, fill tank w/ AHC fluid. If Ok, go to 2.
2. Check operation of the AHC pump & motor: disconnect the AHC pump & motor connector (the big black one w/ 2 thick wires), connect + battery lead to terminal 2, neg to terminal of the AHC pump, and verify that the motor operates. You did this. If NG, replace AHC pump & motor. If OK, go to 3.
3. Bleed air from AHC and AVS hydraulic system: Short pins Ts and E1 of DLC1. Push the down button of the height select switch at least 5 times within 5 sec of starting the motor. Verify the 0.25 sec flashing "off" light. Set damping mode to "comfort," push and hold the "up" button of the height select switch for 10 seconds. "Hint: at this time, the AHC motor relay comes on to raise the front of the vehicle and air inside the AHC & AVS hydraulic system start to bleed with the pump motor operating." Do not raise the vehicle height higher than "HI" in the active test. Turn ignition off, disconnect short on DLC1.
4. Check AHC motor relay: Remove AHC relay from engine J/B. Check continuity between each pair of terminals. Pins 1 & 2 (opposite sides) should be open, pins 3 & 4 (opposite sides) should be 62ohms. If you pull the relay off and look at the bottom, pins 2 & 4 are on one side, pins 1 & 3 are on the other. Pin 1 is opposite of pin 2, pin 3 is opposite of 4. Now apply battery power between pins 3 & 4. Verify that pin 1 & 2 are now shorted. If NG, AHC relay is bad. If OK, go to 5.
5. Check for open and short circuit in harness and connector between fluid pressure sensor and suspension control ECU. Unfortunately, this is a PITA since the ECU is behind the dash. If NG, replace harness or connector. If Ok, go to 6. I find this very unlikely.
6. Check fluid pressure sensor: Start engine and push the vehicle height select switch to select "N" mode. Measure the voltage between terminals 2 & 3 of the fluid pressure sensor connector. Voltage should be 1.48-1.85V. If NG, replace fluid pressure sensor. If OK, clear the DTC.
FYI, there's a DTC 63 & 64 (fluid pressure abnormality--valve does not open). If DTC 64 is detected, the ECU prohibits the accumulating and releasing of pressure of the height control accumulator. If DTC 63, the height control is disabled after certain conditions on differences in wheel height are met.
The one difference I noticed in reading this section vs. the section on performing the active test is it says the relay won't kick on until you've depressed the "UP" button for 10 seconds. I would try this before anything else since it's the easiest, plus you're on step #3 in the checklist.
1. Check fluid level of resevoir tank. If NG, fill tank w/ AHC fluid. If Ok, go to 2.
2. Check operation of the AHC pump & motor: disconnect the AHC pump & motor connector (the big black one w/ 2 thick wires), connect + battery lead to terminal 2, neg to terminal of the AHC pump, and verify that the motor operates. You did this. If NG, replace AHC pump & motor. If OK, go to 3.
3. Bleed air from AHC and AVS hydraulic system: Short pins Ts and E1 of DLC1. Push the down button of the height select switch at least 5 times within 5 sec of starting the motor. Verify the 0.25 sec flashing "off" light. Set damping mode to "comfort," push and hold the "up" button of the height select switch for 10 seconds. "Hint: at this time, the AHC motor relay comes on to raise the front of the vehicle and air inside the AHC & AVS hydraulic system start to bleed with the pump motor operating." Do not raise the vehicle height higher than "HI" in the active test. Turn ignition off, disconnect short on DLC1.
4. Check AHC motor relay: Remove AHC relay from engine J/B. Check continuity between each pair of terminals. Pins 1 & 2 (opposite sides) should be open, pins 3 & 4 (opposite sides) should be 62ohms. If you pull the relay off and look at the bottom, pins 2 & 4 are on one side, pins 1 & 3 are on the other. Pin 1 is opposite of pin 2, pin 3 is opposite of 4. Now apply battery power between pins 3 & 4. Verify that pin 1 & 2 are now shorted. If NG, AHC relay is bad. If OK, go to 5.
5. Check for open and short circuit in harness and connector between fluid pressure sensor and suspension control ECU. Unfortunately, this is a PITA since the ECU is behind the dash. If NG, replace harness or connector. If Ok, go to 6. I find this very unlikely.
6. Check fluid pressure sensor: Start engine and push the vehicle height select switch to select "N" mode. Measure the voltage between terminals 2 & 3 of the fluid pressure sensor connector. Voltage should be 1.48-1.85V. If NG, replace fluid pressure sensor. If OK, clear the DTC.
FYI, there's a DTC 63 & 64 (fluid pressure abnormality--valve does not open). If DTC 64 is detected, the ECU prohibits the accumulating and releasing of pressure of the height control accumulator. If DTC 63, the height control is disabled after certain conditions on differences in wheel height are met.
The one difference I noticed in reading this section vs. the section on performing the active test is it says the relay won't kick on until you've depressed the "UP" button for 10 seconds. I would try this before anything else since it's the easiest, plus you're on step #3 in the checklist.
I would love to know what ultimately fixed your issue in the end. I just completed step 4.
I can't seem to get the height of the car to change while in the active test. I can run the pump manually with 12v directly hooked up to the pump and the relay works.
Also, my lx470 went into the Low condition while on a long road trip. I'm ran it for atleast 5 hours since the condition started, but now have parked it in the garage. I am not on bump stops or anything. Does anyone have an experience as to how long I can keep driving it like this? I need to take it to a cabin 3 hours away loaded with people and luggage. I'm thinking I'm ok, but ya never know.
I can't seem to get the height of the car to change while in the active test. I can run the pump manually with 12v directly hooked up to the pump and the relay works.
Also, my lx470 went into the Low condition while on a long road trip. I'm ran it for atleast 5 hours since the condition started, but now have parked it in the garage. I am not on bump stops or anything. Does anyone have an experience as to how long I can keep driving it like this? I need to take it to a cabin 3 hours away loaded with people and luggage. I'm thinking I'm ok, but ya never know.
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2001LC
SILVER Star
It's under the hood on RH fender, center area, high, near hood. About 4 x 1" black box. Look close and you'll see top is hinged. Flip open top, and you'll see pin holes. It not a CPU. It's a port for diagnostic work.
Does anyone know what shorting Ts and E1 on the DLC1 (Diagnostic Plug) is actually doing??
uHu
Bridgeburner
It puts the AHC ECU in a mode for input signal checking, and for the Active Test (up/down at front and rear individually).
I have been struggling to find out why the AHC is not working on my 2000 LX470 (190K). It is relatively new to me having been owned by my BIL in Phoenix (no rust) and well maintained at dealer. I have read through the AHC threads and tested and eliminated problems with relays (in engine and under dash), all 6 fuses, switches, pump. The issue is that the lights flash to go up or down but nothing ever happens. The pump never runs. I connected E1 and Ts pins and got the flashing lights but raising and lowering did nothing. Pump runs when I connect to power.
I got TechStream working. A challenge by itself but I was able to see readings as below. I could not find anything on bad AHC ECU in the posts but am beginning to suspect that could be the issue. What would you gurus recommend next?
I got TechStream working. A challenge by itself but I was able to see readings as below. I could not find anything on bad AHC ECU in the posts but am beginning to suspect that could be the issue. What would you gurus recommend next?
I just dealt with this identical issue. Lights flash, truck wouldn't move, perpetually stuck in N. I figured it was bad globes (truck is new to me so no backstory) so replaced them, all fresh fluid, cleaned the reservoir, and rebuilt the pump. Still nothing. Ahhhhh. Also, what struck me as very strange was that the truck was bottomed out on the bump stops (since I completely drained the system) but the indicator light continued to show that it was in the N position.
The manual got me nowhere. I bled the system a bunch but that didn't fix anything. Here's what fixed it though.
I removed and reseated the AHC relay in the fuse box. Then I went over to the AHC pump and disconnected the power connector. I started the truck up with the pump power disconnected, and that obviously the an error and shut the system down (AHC OFF light came on). I then turned off the truck, reconnected the power to the pump, and turned the truck back on. Voila. It immediately registered the light at the L position. A push of a button and 20 seconds later, the truck was in H.
Wise man once said "if s*** broke, unplug then plug back in".
I finally was back home and tried this but no luck. Interestingly when I disconnected the pump I did not get an error. I tried running the pump directly from the battery but it appeared to be drawing too much power so I stopped. Not sure of next steps.
Are you sure you disconnected the power harness from the AHC pump? There are 3 connectors there, the power is the most forward connector. ABCs of AHC has good pics that you can reference.
If that was done (relay and power disconnected and then car turned on) and it didn't throw an error, you may want to run techstream and see if the system is operating and reporting.
Edit : I just reread your earlier posts. Your techstream is showing zero across all pressure sensors. I'm not sure what to make of that -maybe someone else can chime in there. It would likely be worth it to start a new thread and ask if anyone else has ever seen that. I didn't have texhstream until after my issue was fixed so I'm not sure whatmine was reading / reporting before the reset.
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hey mtb,
today while fooling with my ahc i notice two things that had me panicking. the system will not operate if it thinks that a door is open. it will also not operate without the truck running. lastly, if i am at a dead stop with my foot on the brake, it will not operate until my foot comes off the break.
maybe i missed these in the fsm? but as soon as i had all doors properly shut (my kids left on of the back doors cracked, just enough to not catch the sensor and my foot off the brake with the motor running, i was back in business. hope this helps.
Thank you for the information and your time to reply. Now it makes sense. So I should be able to bleed the air from the newly installed front accumulators after lifting the front with this active test and shutting off the engine? Then bleeding the rear separately while applying the active test to the rear after lifting the rear after shutting off the engine? I had to remove the front drivers side accumulator for access to the Main cylindrical accumulator for replacement on the frame below the drivers seat. I have blead the new Main accumulator under the seat after also replacing the rusted through short line that comes from the Main Accumulator to the Control Valve on the inside side of the frame below the driver set. The short line feeds pressure from the Main Accumulator to the Control Valve, then it looks like from there it feeds the spherical / round accumulators at each wheel... (Should I bleed the short line going to the Control Valve first?? Or will it eventually bleed out while bleeding the spherical accumulators at each wheel? ( You may wonder why I have not finished the job on my Cruiser yet!) Well my sons 2016 Tacoma 4x4 developed a major rear seal leak requiring my Lift to pull the transmission and repair it. Well with 1030,000. miles on it we decided to pull the engine and replace the chains as well as a seeping water pump we noticed as well..... Your insight is greatly appreciated .........
