AHC pump out? With code 1762 (3 Viewers)

[IndroCruise]

My motor is dead. It measures short circuit between the terminals. So apparently it can burn out from overuse without any failsafe kicking in and more importantly, without the fuse burning! I will be trying out an entire assembly with the motor, pump, reservoir, etc, removed from another car tomorrow and might try to have my motor rewound as a spare.

I hesitate to make suggestions to someone of your LC100 and AHC/TEMS experience @Moridinbg -- but I do wonder, given the kilometres on your vehicle, whether you might be one of the few who actually have 'worn out' the motor driving the AHC Pump -- meaning, worn brushes or worn commutator or maybe accumulation of detritus inside the motor leading to shorting of the windings at the commutator segments?

Many of us have written extensively about the AHC Pump but there are very few posts about the motor. The link below is the only remotely relevant post I can find -- it reveals some helpful pictures but not much else -- but maybe it is enough to justify further investigation:

AHC help ... yeah another one.

Hey ... Yep another ahc post .... last year I bought new spheres etc fitted em and cleaned the pump assembly everything was fine. This year I decided to do my yearly ahc bleed / flush. Went well everything was OK then one day car was parked a few days and when I went to drive it suspension...

forum.ih8mud.com

If your whole AHC Pump/Motor assembly has or will be removed, maybe it is worth going a little further to dismantle the motor?

Your views on whether this is worthwhile or anything you find will be of great interest.

 

[Moridinbg]

I got the pump/motor/reservoir assembly from a vehicle with a working AHC system. After I removed mine, turns out the motor is working. When applying 12V it spins. When spinning by hand it doesn't turn smoothly.

Anyways, I decided to replace the entire assembly with the donor. I also got a new Techstream cable.

Shorting Ts & E1 in the engine bay, as in your screenshot @IndroCruise, got me into diag mode. The online FSM at LC100 Workshop Manual - https://lc100e.github.io/ tells me to short Ts & CG in the OBD plug in the cabin. That didn't work on my HDJ100. But I do not seem to be getting any response from the active test? Hard to say if the pump motor even engages with the engine noise, but definitely nothing moves.

Reading back through the thread, I have very similar symptoms to parkeyjack - 1762 immediately, two motor/pump assemblies that do not work and active test that does nothing. He at least had one pump that worked slowly... I am starting to think that it might be not the pump, but something else.

 

[Moridinbg]

What a challenge that AHC issue was... I didn't take almost any pictures, as I was under lots of stress and covered in oil to the ears. Pictures here are from other posts, but are a good illustration.

First of all - if you are getting 1762 immediately after starting the car with a new pump - 99% the pump is not assembled correctly and is just spinning and not pumping anything.
The two notched cylinders in the bottom of the photo go around the two gears. They can go on either gear, but notice the indentation on the right one. It has to end up between the strainer and the indentation inside the rounded triangle ring. If it does not you can still assemble everything but no oil will come out.

Before installing the new assembly, 100% apply 12V to the motor and check that it is pumping out a steady stream of oil. It's not a particularly strong stream, but it is steady and shoots out at 10-15cm/4-6" (don't quote me on the exact distance)

Before installation 100% take the pump apart and clean it up. Lots of residue inside even on otherwise clean assemblies with clear fluid. The pump is super sensitive to blockage and contaminations. Those pumps run crazy high pressures - 7Mpa, which is the target front pressure is 70bar or 70 times the air pressure, or 700m underwater!
The strainers are extra fine in order to protect the gears and are easy to block, even with fine residue. If the pump is making screeching noises and/or the stream of oil is not steady, high chances are that it is at least partially blocked. I did not try to force them out, but blew them with compressed air.

Do not take the motor apart unless you really have to. 90% of the time the problem will be within the pump. You will need a press to put it back together or rig some ghetto system. The rotor shaft is pressed inside the output bearing, which is pressed inside the housing. The brushes are spring loaded and you can't put the rotor inside them, without first removing it from the housing. You will then have to press the brushes + rotor back inside the housing.
Mine is at 280k miles and it very well has > 50% of the brushes left and the commutator looks pristine. More or less exactly like the photo bellow.

The symptoms I had that were giving me a lot of grief:
- Active test does nothing - this was improperly assembled pump.
- Active test makes a lot of noise, but vehicle barely moves. Pressure barely reaches 1.5-2MPa - this was debris in the pump - a hair (!) and some strings, probably from the rags.

Make sure to manually bleed at each corner once the pump works well. Messing around with it, with the piping, priming it with air still inside, etc will add some air to the system.

 

[IndroCruise]

What a challenge that AHC issue was... I didn't take almost any pictures, as I was under lots of stress and covered in oil to the ears. Pictures here are from other posts, but are a good illustration.

First of all - if you are getting 1762 immediately after starting the car with a new pump - 99% the pump is not assembled correctly and is just spinning and not pumping anything.
The two notched cylinders in the bottom of the photo go around the two gears. They can go on either gear, but notice the indentation on the right one. It has to end up between the strainer and the indentation inside the rounded triangle ring. If it does not you can still assemble everything but no oil will come out.

Before installing the new assembly, 100% apply 12V to the motor and check that it is pumping out a steady stream of oil. It's not a particularly strong stream, but it is steady and shoots out at 10-15cm/4-6" (don't quote me on the exact distance)

Before installation 100% take the pump apart and clean it up. Lots of residue inside even on otherwise clean assemblies with clear fluid. The pump is super sensitive to blockage and contaminations. Those pumps run crazy high pressures - 7Mpa, which is the target front pressure is 70bar or 70 times the air pressure, or 700m underwater!
The strainers are extra fine in order to protect the gears and are easy to block, even with fine residue. If the pump is making screeching noises and/or the stream of oil is not steady, high chances are that it is at least partially blocked. I did not try to force them out, but blew them with compressed air.

Do not take the motor apart unless you really have to. 90% of the time the problem will be within the pump. You will need a press to put it back together or rig some ghetto system. The rotor shaft is pressed inside the output bearing, which is pressed inside the housing. The brushes are spring loaded and you can't put the rotor inside them, without first removing it from the housing. You will then have to press the brushes + rotor back inside the housing.
Mine is at 280k miles and it very well has > 50% of the brushes left and the commutator looks pristine. More or less exactly like the photo bellow.

The symptoms I had that were giving me a lot of grief:
- Active test does nothing - this was improperly assembled pump.
- Active test makes a lot of noise, but vehicle barely moves. Pressure barely reaches 1.5-2MPa - this was debris in the pump - a hair (!) and some strings, probably from the rags.

Make sure to manually bleed at each corner once the pump works well. Messing around with it, with the piping, priming it with air still inside, etc will add some air to the system.

Seems like speedy and impressive solution-finding already achieved @Moridinbg – great work!! I had started writing some speculations and observations which are now too late for the party, but here they are anyway. The pictures further below concerning AHC Pump details and issues as resolved by @Moridinbg may be of interest to others whose searches may come this way.

Observations on reported symptoms:

• Spinning the pump by hand is not smooth. [Seems normal, there will be a ‘lumpy’ feel as the different separate rotor coils pass the permanent magnets in the motor case and make and break connections at the commutator when spinning by hand].
• Pump spins with 12 volts connected. [Seems likely that pump motor is OK].
• “Active Test” does not work – should be able to hear or feel pump operating. [Seems likely that break in circuit, or, ECU has activated one of the ‘fail safe functions’ for some reason – and AHC Main Relay is prevented from operation, so power cannot arriving at motor via AHC system nor under “Active Test”. See also notes below about “Active Test” via DLC3 and via DLC1],
• DTC C1762 has appeared – “Fluid Pressure Abnormality – Pump & Motor Does Not Supply Fluid”,
• DTC C1751 has not appeared – “AHC Pump and Motor Circuit”,
• DTC C1741 has not appeared – “AHC Motor Relay Circuit”,

Suggest consider whatever seems relevant from the usual preliminary mental and/or physical checklist:

1. Re-boot vehicle by disconnecting and reconnecting battery,
2. Clear all DTC’s and observe reappearance of persistent DTC’s,
3. Check no faulty door switches or faulty rear hatch switch are sending a ‘door open’ signal to ECU,
4. Check switch at brake pedal is working correctly, not sending lengthy ‘brakes are ‘on’’ signal to ECU,
5. Check steering angle sensor is giving reasonable readings for steering straight ahead (<36 degrees),
6. Check condition of all Height Control Sensors – can easily have aberrant behaviour and or ‘fail safe function’ (no AHC operation) even without appearance of DTC’s C1711, C1712, C1713,
7. Check power supply continuity at:
8. 50 Amp AHC fuse in Junction Box in engine bay,
9. 15 Amp AHC-B fuse in Junction Panel behind cowl forward of LHS Front Door,
10. 20 Amp AHC-IG fuse in Junction Panel behind cowl forward of LHS Front Door,
11. Check operation of AHC Relay in Junction Box in engine bay,
12. Check that connectors tight at the Suspension Control (AHC) ECU under dashboard,
13. Check Techstream with AHC “ON” looking for listing showing “Main Relay Expectation – ON”,
14. Check operation of AHC Main Relay attached to Suspension Control (AHC) ECU under dashboard,
15. Check Pressure Sensor is healthy per FSM method even if DTC C1718 is not reported,
16. If fuses, relays and power circuits and Pressure Sensor as above are healthy, focus on other causes of DTC C1762 -- “Fluid Pressure Abnormality – Pump & Motor Does Not Supply Fluid”, noting that this fault has very fast response, about 0.6 seconds, because it is meant to protect the gear pump from destruction (cannot see a relief valve in this hydraulic circuit, unusual omission for a gear pump). Causes may be one or more of:
17. Power Source Circuit – may require “Pre-check”, especially “Input Signal Check” per FSM Diagnostic section,
18. Connector or wiring harness break – may require review of correct voltages at ECU connectors per “Terminals of ECU” at FSM Page DI-218 to establish which circuit contains the problem,
19. nitrogen from failing ‘globe’ membranes leading to gas accumulating in pump, aeration and pressure loss, possible cavitation,
20. failed motor-pump seal or failed reservoir-pump seal leading to air entrainment in pump, aeration and pressure loss, possible cavitation,
21. whole or partial blockage within AHC Pump at one or more of the three (3) internal strainers -- fluid intake strainer (most likely), or secondary strainer above intake or third strainer within Return Valve -- leading to overpressure recognised by Pressure Sensor and DTC1762,
22. over-tightened bolts attaching AHC Pump to manifold carrying pump and motor restrict pump rotation,
23. wrongly oriented slot (or notch) at base of gear case within AHC Pump, also leading to low delivery pressure and flow recognised by Pressure Sensor and DTC C1762. The notch must face towards the inlet side (low pressure) side of the pump, not the discharge side (high pressure side) of the pump.

Occasionally questions arise about use of the “DIAGNOSTIC” interface DLC1 or the OBD2/MOBD interface DLC3 for diagnostic purposes. As explained in posts elsewhere, either can be used for some tasks but not simultaneously. See links below for further information posted long ago by @PADDO.

“Active Test” and other tests at “DIAGNOSTIC” interface DLC1 in engine bay for convenience per LX470 FSM:
AHC C1751 & C1762 Help/Recommendations/Suggestions - https://forum.ih8mud.com/threads/ahc-c1751-c1762-help-recommendations-suggestions.997555/#post-11094843
and
Suspension problem even after replacing almost everything - https://forum.ih8mud.com/threads/suspension-problem-even-after-replacing-almost-everything.812905/page-2#post-9293631

Assertion by @PADDO about equivalent connections using “DIAGNOSTIC” interface DLC1 in the engine bay and “OBD2” interface DLC3 under the dashboard. [I have used the bridging method at DLC1 on my HDJ100R (with 1HD-FTE turbodiesel) many times, so I am confident that the references by @PADDO are not limited only to UZJ100 (with 2UZ-FE gasoline). I have never tried “Active Test” via Techstream nor via bridging at DLC3 – too inconvenient!].
Changing out the AHC suspension fluid? - https://forum.ih8mud.com/threads/changing-out-the-ahc-suspension-fluid.60619/page-10#post-12134746

Recommendation by @PADDO when DTC C1762 found:
AHC C1751 & C1762 Help/Recommendations/Suggestions - https://forum.ih8mud.com/threads/ahc-c1751-c1762-help-recommendations-suggestions.997555/#post-11092142

Suggestion on Re-booting Procedure:
AHC DTC C1743 - main relay - https://forum.ih8mud.com/threads/ahc-dtc-c1743-main-relay.914138/#post-10245382

 

[BullElk]

Thread reviving with enlightening info… to me.

The issue I had in the original post of this thread has happened again now with a different pump. Which was and is now…LX lowered and will not elevate. Getting code 1762, abnormal fluild pressure.

I took pump apart several times making sure it was clean with no sludgy gel, motor running fine with direct power, good fluid, bled air from lines, bled air from attenuator, proper voltage from wire connectors and pressure sensor, would not “active test” etc., etc.

Kept thinking the pump is what creates and maintains pressure with good running motor. But what could possibly malfunction inside a simple block of metal with only small holes throughout and two small smooth running gears ? O-RINGS

I went to Harbor Freight and bought the metric O ring assortment box for $5. Using the pump that went out the first time three years ago, I replaced the two small O rings with two that were just a bit fatter as well as the large ring between motor cover and block. I did not replace the weird shaped “ring”.

I cranked truck and the pump came to life. It now raises and lowers perfectly with 14 graduations between levels and no codes. Hopefully it will stay that way.

Like other issues with these vehicles, the large majority of the time it ends up being a pretty simple solution.