Food for the "AHC is unreliable and it can get you stranded in the middle of nowhere" crowd, I guess.
I am in the middle of nowhere in Argentina and I am getting C1762 after trying to rise the vehicle to H. It almost got to the expected height, then aborted and dropped to N. After clearing the code, it made a screeching sound before throwing it again. After doing this a couple of times the Accumulator pressure dropped to 0.
I tried to crack the line between the pump and the attenuator sitting on the chassis rail, as per suggestion in another thread (
AHC C1762 - https://forum.ih8mud.com/threads/ahc-c1762.635036/#post-8001027). Some fluid got out, this almost seemed to work, but then after trying to go to H it suddenly dropped all the way to L and the reservoir is full of fluid pretty much to the brim. Now clearing the error results in it coming back almost immediately and no more screeching noises. Cracking the accumulator bleeders results in almost no fluid coming out, not surprising being in L.
The active test with the diagnostic port in the front doesn't move it either.
The bleeder on the accumulator broke of ages ago, so can't use that. I had bled the system multiple times via only the globes and it was fine. I went through a pump replacement some months ago and could bleed it without touching it either. I have been thinking about cracking the line going into the accumulator next.
I raised the car to H 4 days ago to change the oil and there were no issues or noises.
Any help and advice would be appreciated. The 100 series seems to have never been sold in Argentina or Chile, dealers and mechanics are totally clueless and there are pretty much 0 spare parts available here. I had to wait almost a month to get a tie rod via DHL.
Hi
@Moridinbg – I have followed your various threads and posts over the years and admired the work. You have an intimate and comprehensive knowledge of your HDJ100L vehicle, including a full understanding about how the AHC and TEMS systems work. The current experience must be so tough and frustrating given your from-the-ground-up rebuild and given the preparation you have done prior to arriving in South America!!
The following notes do not tell you anything that you do not already know. They may help you to frame or cross-check your own thoughts.
A quick summary of reported symptoms seems to be:
- AHC Pump starts but operates only briefly,
- AHC Pump screams (meaning cavitation or aeration),
- DTC 1762 quickly reappears after clearing, on each start-up,
- Possibly impaired flow rate from AHC Pump – suggesting internal blockage of AHC Pump, or, AHC circuit blockage downstream from the pump,
- Vehicle has descended to “LO” height and remains stuck in this position – AHC Pump is not operating continuously, cuts out with C1762 (pressure abnormailty), so vehicle will not raise,
- “Active Test” procedure using Techstream method, or, using the manual paperclip-at-DLC1 method, does not cause the AHC Pump to start – cannot raise vehicle by either "Active Test" method,
- AHC and TEMS systems appear to be in one or other “fail safe function” as confirmed by refusal to respond to “Active Test” – although exact cause is unclear,
- No other DTC’s are reported,
- AHC pressures cannot be measured because the vehicle cannot raise from “LO” to “N” height, so AHC pressure test is impossible,
- broken bleeder valve on Height Control Accumulator -- possibility of impaired 'bleeding' and trapped air?
- the symptoms have worsened progressively, following the initial failure.
What should be made of all this??
Firstly, the vehicle is heavily loaded – so if not already done, suggest a close underbody check of the
mechanical suspension components, looking for failures such as mountings and torsion bar adjusters, torsion bar attachments to front Lower Control Arms, rear coil spring seats, various bushings. Basically, check for any damage or wear-and-tear which could have allowed transfer of excess weight away from the springs/torsion bars to the AHC system, possibly resulting in excessive AHC pressures beyond the capability of the AHC Pump.
Secondly, it does have to be said that any event of “fail safe function” causes suspicions about one or more faulty or damaged
Height Control Sensor circuits. This is not the only cause but it is a common cause, especially if these Sensors have seen many years or kilometres or miles in adverse conditions, and have accumulated internal wear and/or electrical degradation.
When one or more of the Height Control Sensor circuits transmit a wrong voltage to the Suspension ECU for the height set at the console switch (“LO”, “N”, “HI”), then some crazy and inconsistent responses by the vehicle are possible, as known from multiple IH8MUD reports. The FSM Diagnostics for Height Control Sensors are quite clear. Lack of any DTC’s (such as C1711, C1712, C1713) relating to Height Control Sensor circuits means only that the signal received by the Suspension ECU is within the acceptable FSM-specified range of 0.3 volts to 4.7 volts. A degraded Height Control Sensor easily can be the source of a signal which is within this FSM-specified range
but is the wrong voltage for the “LO”, “N” or “HI” height setting at the console switch. In such cases, there will be no DTC even though the Height Control Sensor circuit is faulty.
Height Control Sensor circuits arouse particular suspicion when some or all of the vehicle arrives at a strange height and the vehicle refuses to respond to AHC controls, without these DTC's, as has happened in this case.
Therefore, suggest at least visually inspect in place, and preferably test electrically, all three Height Control Sensors circuits (where ‘circuit’ means Sensor plus Connectors plus Harness).
Next, I agree with
@suprarx7nut – it is important to be satisfied about whether the symptoms are a result of
air or nitrogen gas in the AHC system -- either
- dissolved or entrained air in the AHC Fluid, or,
- trapped air in the system, especially if there have been limitations in ‘bleeding’ the Height Control Accumulator due to its broken bleeder valve,
- suspicions about air caught around the Attenuator -- or perhaps gel blockage in the Attenuator. This seems unlikely. The Attenuator is no more than a ‘shock absorber’ which smooths pressure waves (in a similar way to a ‘water hammer’ protector in a Building). The Attenuator either works or it doesn't -- but it is hard to imagine it causing a blockage. However, the joins here can be a convenient place to break the line to observe and release air or gas,
- nitrogen gas escaping from failing ‘globes’ -- seems unlikely if the ‘globes’ are relatively new????
However, to deal with any air or nitrogen gas issues by ‘bleeding’ requires the AHC Pump to be working without cutting out due to C1762 (pressure abnormailty) -- so that the ‘bleeding’ can be done and ideally so that the vehicle can be raised. More about the AHC Pump later.
After considering all of the above, when the AHC/TEMS system suddenly stops, it usually means that
- a fault or sensor or relay or fuse failure has occurred in either the AHC Pump, or the AHC system, or both, and power is not being received,
or,
- one of the ‘fail safe functions’ has been initiated correctly by the Suspension Electronic Control Unit (ECU) – the various ‘fail safe functions’ are explained with each fault condition listed in the FSM Diagnostics section for the AHC/TEMS system. While the exact cause is described slightly differently in each case, nearly all of them result in the non-operation of the AHC/TEMS systems, with a few variations on how heights and damping are set while in each particular condition. The "fail safe" condition has to be resolved and the DTC cleared before the AHC/TEMS systems will operate correctly again. Some faults may not report a DTC -- as mentioned, the Height Control Sensors are the most famous in this regard -- best to treat these items with suspicion, visually examine them, then electrically test them,
or,
- in rare circumstances, it may mean that Suspension Electronic Control Unit (ECU) has given up -- possible but unusual, suggest consider other possibilities first.
This just leaves the small problem of trying to figure out the actual cause!
A starting point is to consider whatever seems relevant from the usual preliminary mental and/or physical checklist.
Most likely this has been done already and
the practical starting point may be Step 15 and onwards in the list below – noting that the AHC Pump starts only briefly, AHC Pump screams (meaning cavitation or aeration or mechanical interference), DTC 1762 quickly reappears after clearing before each start-up, vehicle has descended to “LO” height and remains stuck there, etc:
- Re-boot vehicle and ECU by disconnecting and reconnecting battery,
- Use the manual procedure to clear all DTC’s and observe reappearance of faults,
- Check no faulty door switches or faulty rear hatch switch are sending a ‘door open’ signal to ECU,
- Check switch at brake pedal is working correctly, not sending lengthy ‘brakes are ‘on’’ signal to ECU,
- If possible, check steering angle sensor is giving reasonable readings for steering straight ahead (<36 degrees),
- Inspect physical condition of all Height Control Sensor circuits and test electrical condition of each Sensor circuit per FSM – can easily have aberrant behaviour and or ‘fail safe function’ (no AHC operation) even without appearance of DTC’s C1711, C1712, C1713,
- Check power supply continuity at:
- 50 Amp AHC fuse in Junction Box in engine bay,
- 15 Amp AHC-B fuse in Junction Panel behind cowl forward of LHS Front Door,
- 20 Amp AHC-IG fuse in Junction Panel behind cowl forward of LHS Front Door,
- Check operation of AHC Relay in Junction Box in engine bay,
- Check that connectors tight at the Suspension Control (AHC) ECU under dashboard,
- Check operation of AHC Main Relay attached to Suspension Control (AHC) ECU under dashboard,
- Check Pressure Sensor is healthy per FSM method even if DTC C1718 is not reported,
- If fuses, relays and power circuits and Pressure Sensor circuits 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. Causes may be one or more of:
- Check Power Source Circuit – may require “Pre-check”, especially “Input Signal Check” per FSM Diagnostic section – or the equivalent method which utilises DLC1,
- Check Connector or wiring harness break – may require review of correct voltages at ECU connectors per “Terminals of ECU” page at FSM to establish which circuit contains the problem,
- Consider age of ‘globes’ and possibility of nitrogen from failing ‘globe’ membranes leading to gas accumulating in pump, aeration and pressure loss, possible cavitation,
- Consider failed motor-pump seal or failed reservoir-pump seal leading to air entrainment into pump, aeration and pressure loss, possible cavitation,
- Consider damaged or slipping ‘drive-shaft’ between AHC Pump and Motor,
- Consider whole or partial blockage within AHC Pump at one or more of the two (2) internal strainers – (i) fluid intake strainer (most likely), or, (ii) secondary strainer above intake, either of which may lead to pressure abnormality recognised by Pressure Sensor and DTC1762,
- Consider whole or partial blockage within the Return Valve strainer within the Return Valve which also could lead to pressure abnormality recognised by Pressure Sensor and DTC1762 (reported in some Russian sources but never noticed in IH8MUD posts??),
- Consider over-tightened bolts attaching AHC Pump sub-assembly to the manifold carrying pump and motor on either side -- if too tight, may restrict pump rotation and limit fluid supply to AHC system,
- Investigate 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. [This is particularly relevant if AHC Pump has been dismantled or comes from a second-hand source and history is unconfirmed],
If there are concerns about the
AHC Pump sub-assembly, Part Number 48901-60010 (
not the whole Pump-Motor-Manifold-Tank-Sensors assembly Part Number 48910-60012), then the most reliable course of action is to replace with a new Pump sub-assembly 48901-60010 (Impex: USD103.91 or Partsouq: USD173.49 – plus delivery in both cases).
Where this is not possible -- such as at your current location in Patagonia -- or if a second-hand pump has been or will be used, suggest dismantle the pump, inspect internally for gel, grit, gear damage or wear (eg from cavitation or foreign material), gear housing wear or damage, appearance of other debris -- and clean all the AHC Pump components. My pictures at the link mentioned above by
@suprarx7nut give the idea.
The progressive deterioration of the reported symptoms may be indicative of a progressive build-up of a blockage in the AHC system -- until eventually the system reaches a trigger-point and has a "heart attack".
The most common blockage points are the two strainers
within the AHC Pump sub-assembly:
(i) the Inlet Strainer: This deals with incoming AHC Fluid from the AHC Tank before it enters the actual gears in the pump and is the primary blockage position. AHC fluid returns from the AHC system when the Levelling Valves open on instruction from the Suspension ECU. The fluid then returns directly to the AHC Tank, as directed by the Return Valve, and the vehicle sinks. The fluid returning from the AHC system is able to flow around the outside of the AHC Pump sub-assembly and inside the outer cover but it does not go back to the pump until the pump draws fluid from the Tank. When the Levelling Valves are closed, the pressure behind the outer cover is at Tank Pressure (basically atmospheric pressure). It is in this low flow situation behind the outer pump cover that, over time, an build-up of sludge can develop behind the outer cover. Some of this sludge eventually finds its way back to the AHC Tank during cycling of the AHC system. During operation of the AHC Pump, some of this 'sludgy' fluid is drawn into the AHC Pump, where it is arrested by the Inlet Strainer. Over time (10+++ years??) the Inlet Strainer will progressively become blocked and eventually impair pump performance. (The maintenance remedy, neglected by many, is periodic replacement of AHC Fluid. This also would be the ideal time to remove the outer cover and clean out the sludge, given that the whole system is 'bled' again during an AHC Fluid change).
(ii) the Bypass Strainer: This deals with fluid caught between the pump teeth passing through the centre of the pump after the gears have meshed. This small flow exits via the gear case clearances, then through the bypass strainer, and returns to the Inlet side of the pump.
There is no strainer on the discharge side of the AHC gear pump sub-assembly itself.
See more details and further pictures at Post #10, Post #12 and Post #15 at:
AHC pump removal with pics - https://forum.ih8mud.com/threads/ahc-pump-removal-with-pics.1227554/#post-14710306
The strainers can be backwashed with a suitable solvent and this gives at least a partial clean. The better idea is to use a tapered wood screw of a suitable diameter to engage the brass collar of the strainer and withdraw the strainer from the pump body, gently but with some force -- see pic below. The point of the screw must not be too long so as to avoid damage to the fabric mesh of each strainer. The fabric mesh of the two strainers then can be washed thoroughly in a suitable solvent and replaced back in their positions in the pump.
It is vital that the AHC Pump be re-assembled with the “notch” or “slot” visible on one of the gearcases placed so that it is on the Inlet side of the pump, and below the bypass strainer. The pump will operate poorly, if it operates at all, if the “notch” or “slot” is placed wrongly on the discharge side of the pump.
There is a
third strainer at the Return Valve located within the milled aluminium manifold supporting the AHC Pump on one side and the Motor on the other side. All fluid discharged by the AHC Pump passes through this strainer in the Return Valve on its way downstream into the AHC system. Fluid
returning from the AHC system
does not pass through this strainer but bypasses directly to the AHC Tank as directed by the Return Valve. This means that when blowing back through the coiled pipe to the pump, the effort
does not go through the pump; instead the Return Valve causes this effort to go directly to the AHC Tank. Similarly, if the AHC Pump is run in reverse while connected and in place in the vehicle, the pump can churn -- and most likely will cavitate noisily -- but the Return Valve prevents the pump ‘sucking’ fluid from the AHC system. The Return Valve is opened only by positive pressure from the AHC Pump. That is, the pump Discharge cannot become an Inlet (unless there is leakage around the o-ring at the normal pump discharge point).
Lastly, I sense that obtaining supplies of genuine AHC Fluid may be a problem at your location. I have NEVER used anything other than genuine Toyota/Lexus AHC Fluid 08886-01805 -- but if stuck and desperate in a remote place I guess would look for a light mineral oil, definitely not anything remotely related to brake fluid.
Here ends this essay. Over to all others for welcome comment or better assistance to
@Moridinbg while stranded in Patagonia.
Maybe
@suprarx7nut,
@LndXrsr,
@2001LC and/or elders of the tribe such as
@uHu or
@PADDO can add further insights??
Withdrawing Internal Strainers in AHC Pump by engaging strainer brass collar with a tapered wood screw:
Return Valve Details with Strainer shown by cross-hatching:
Withdrawing Return Valve Strainer by engaging brass collar with a tapered wood screw:
This gives me another 5-10 seconds of runtime. That way I got it from beyond L (-70mm) to L (-45mm) and then back to N. I tried to bleed all corners, but got only clear fluid. Then went all the way to H. This takes about 10-12 reverse polarities to the motor. Good thing the diesels come with dual starting batteries from the factory 
