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FAQ: Lexus LX470 and Toyota Landcruiser 100 accumulators.


Frequently Asked Questions about the Lexus LX-470 and Toyota Landcruiser 100 suspension systems. (You can leave a question in the comment section and I’ll reply to you there.):

Q: My Landcruiser 100/Lexus LX 470 is riding real bouncy/hard on the front (rear or both ends)—why is that?

A:The Lexus LX470 Automatic Height Control System (AHC) incorporates oil filled ‘shock absorbers’ on each corner. The AHC system adds (or releases) oil from the shock to adjust the height. When you drive over a bump, the oil must go somewhere if the shock is to compress and ‘absorb’ the bump. The place it goes are accumulators—one for each shock.

The Lexus and Toyota accumulators are factory pre-charged with nitrogen to several hundred PSI. The gas is on the top side of an internal diaphragm separating the gas from the AHC oil. The gas slowly leaks through the diaphragm just like air leaks out of a tire, only much slower.

Eventually (after 4 to 6 years, or 50K to 100K miles) enough gas has leaked that the accumulator becomes mostly oil filled-just like the shock. Then, when driving over a bump, the oil has no place to go and the shock cannot compress—and the vehicle gets tossed up and rides real bouncy.

Q:How can I test the accumulators to be sure they are causing the bumpy ride?

A:There are two methods of testing the accumulators. Lexus advises that when you change the height setting from ‘low’ to ‘high’, the oil level in the AHC reservoir should lower by more than 7 graduations on the reservoir (new accumulators will change level by more than 12 graduations.) Since higher pressure is needed to raise the vehicle, some of the oil goes into the shocks to raise the level, the rest into the accumulators, compressing the remaining gas.

The other method is to set the vehicle at normal ride height and then bounce real hard on each corner to see how much the shock will compress. With flat accumulators, there will not be much ‘give.’ New suspension accumulators will allow several inches of movement when you bounce hard on the corner. Another way of accomplishing this is to drive each wheel over a speed bump at about 5 mph and note the ride quality. Good accumulators will have a nearly smooth, well damped movement. Flat accumulators will produce a sharp and bouncy movement and bouncy ride.

Q:Why can’t I just disconnect or deactivate the AHC system?

A: The AHC system is integrated with the Stability Control System to reduce the body roll and sway. Deactivating the system will compromise the vehicle’s roll-over resistance. Also, the oil pressure in the shocks supports a significant part of the vehicle weight and the vehicle height will drop to the minimum height stops and ride extremely harsh.

Q: I understand the Toyota Land Cruiser 100 standard suspension (without AHC) will ‘bolt on’ and can replace my AHC. Why shouldn’t I do that?

A: Without the AHC working as designed, the vehicle stability is compromised and occupants are at increased risk of death or injury if sudden maneuvers are made. The LX-470 and LC-100 are very similar, but the LX-470 has a higher center of gravity due to the upgraded interior insulation, seats and other convenience and comfort features. Your insurance company would most likely deny coverage of any accident involving vehicle loss of control when they discover you have significantly modified your vehicle suspension without notifying them. They will decline to write any coverage at all when you do notify them.

Q: What damage may result if I continue to drive with flat accumulators?

A:Driving with flat accumulators will cause very high transient pressures in the shock absorbers when you go over bumps. This is, of course, very hard on all the suspension components, including the shock absorber mounting bushings.

The system has a safety valve which releases this dangerously high pressure back to the AHC oil reservoir. However, this is not designed for continuous activation. When the high pressure oil is released from the shocks, the vehicle will ride lower than it was. The AHC system will then add oil back to restore the height, requiring the electric oil pump to run.

The AHC computer system has an automatic shut-off to prevent damaging the pump by frequent or continuous running since that would indicate a leak or other damage. Driving on bumpy roads will cause the pump shut-off to activate and the AHC system to switch to default mode. Now when you drive over another bump, oil is released by the overpressure valve, but no oil is added back—and the vehicle level drops lower and lower on each bump.

It will reach a point that when the wheel is in the air after hitting a bump, the spring pushing the wheel back down will cause negative pressure in the oil supply line from the pump. This will suck air into the hydraulic pump past the motor shaft seal. The Lexus factory test procedure will show this condition as a ‘faulty pump’ requiring replacement (at a cost of more than $2500).

Q: Where are the accumulators located?

A: The accumulators are mounted between the front and rear wheels on the outside of the frame rails, under the running boards.

Q: How are the accumulators attached / connected?

A: The accumulators simply screw on and off the control valves mounted on the frame rail. They can be removed easily with either a ‘chain wrench’ or a 36mm open end wrench (spanner) that is no more than 9mm (3/8”) thick.

A: Someone has added water (or windshield washer fluid) to my AHC oil reservoir. What can I do?

A: Water and water based washer fluid will not permanently damage anything-but they will need to be flushed out. A low cost (relative to ACH fluid) Rust and Oxidation (R&O) inhibited hydraulic oil purchased in 5 gallon pail from an auto parts store is a good flushing fluid. Suction the fluid from the reservoir and refill it with clean oil. Then with the vehicle running and height on ‘low’, open the ‘brake bleeder’ on the right front AHC control valve. Continue flushing until the fluid is clean. Then move to the left front, then left rear, and finally right rear in succession. If all the brake bleeders show serious contamination, then it may be advisable to remove each shock and pour the contaminated oil out of them, refill with clean oil and reinstall the shocks. Drive the vehicle a few days and repeat the entire flushing process to ensure all the water has been removed.

Alcohol based (no-freeze) windshield washer fluid will damage the pump because it is a very poor lubricant. It may also attack the oil seals in the system and the accumulator diaphragms. Alcohol must be flushed out as soon as possible.

Brake fluid (glycol-ether type DOT-3 or DOT-4) will damage the oil seals and accumulators and must be flushed out as soon as possible. DOT-5 brake fluid is silicone oil and will not damage anything but needs to be flushed out.

I hope this FAQ has been useful to you. Please ask any questions you may have in the comment section and I’ll be glad to help you out.

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FAQ: Infiniti Q45a Accumulators


Frequently Asked Questions About the Infiniti Q45a Active Suspension.

  • Q: How can I tell if I have bad (flat) accumulators?
    • A: When the strut accumulators are low/flat, the car rides very rough and harsh because the suspension system no longer can absorb bumps. You’ll need to buy replacement accumulators.
  • Q: The ACTSUS warning light is on—what do I do?
    • A: Run the self diagnostics described in ‘Testing the Active Suspension System’ in the Q45a service manual. If you do not have a copy of the service manual, email the error code to me HYPERLINK “” I will email you the diagnosis and suggest what to do.
  • Q: I cannot get the self diagnostics to run—what can I do?
    • A: Disconnect the battery for at least 3 minutes. Sometimes (very rarely) the active system computer will ‘freeze up.’ The active system computer is a long way from the battery (under the rear parcel shelf) and takes a lot of power and is very sensitive to low voltage. A low battery or defective alternator will often cause all sorts of electronic system errors in the Q45a.
  • Q: How can I test the shock (strut) accumulators?
    • A: You can judge the condition of the strut (shock) accumulators by bouncing hard on each corner (with the car running). With good accumulators, there will be 4-5” of smooth suspension travel on the front end, 5-6” on the rear. If the accumulators are flat, there will be little or no free travel—the only ‘give’ is in the tires, suspension bushings, and frame.
  • Q: What about the other accumulators? How do I test them?
    • A: When the main accumulators are low or flat, the car will move up and down with dips, holes, uneven surfaces in the road, just like a standard suspension, but slightly less. With the main accumulators in good condition, the car body moves about 70% less than a standard suspension. Experience has shown the main accumulator and other accumulators are always very low or flat if the strut accumulators are flat. An Infiniti Dealer can perform a detailed test with the CONSULT computer testing system. Expect to spend $200 or more for this test and be sure the technician is familiar with the active suspension system.
  • Q: How long will recharged accumulators last?
    • A: Expect recharged accumulators to last about as long as the original charge—or 50-70,000 miles (4-5 years) depending on road conditions. Rougher roads will, of course, wear them up faster than smooth roads.
  • Q: Can I change just the 4 strut accumulators and get a smooth ride?
    • A: Yes. Exchanging the 4 strut accumulators will restore a smooth ride to your car, provided the active suspension system is working properly (meaning the warning light is off).
  • Q: One (or more) of the struts is leaking oil—what can I do?
    • A: Flat strut accumulators cause extremely high transient pressures in the struts when the car drives over bumps. This can force oil past the strut shaft seals. Those leaks normally stop when the strut accumulators are exchanged with recharged ones. If the dust boots are torn, abrasive dirt can cause wear on the seal and leaks that may not stop. Used struts are available from B&B Suspension.
  • Q: Sometimes my car makes noises like a groan or moan, or rap-rap-rap when going over rough streets. What causes that sound?
    • A: When the car has been driven with flat strut accumulators for some time, and the active system oil has not been changed at least every 60,000 miles, the main pressure control valve and the 4 pressure control valves (one for each strut) will wear. The ‘groan/moan’ is coming from the main pressure control valve (located in front of the left fender well) Sometimes changing the oil will cure the noise. Adding 1 to 2 pints of LUBEGUARD Red to the system reservoir has also proven beneficial to noisy systems. The ‘rap-rap-rap’ sound is ‘water hammer’ caused by stick-slip of pressure control valves, usually the main pressure control valve. Lubeguard Red also helps this noise condition.
  • Q: One corner (or more) sometimes moves up and down on its own. Or the height does not stay steady, or the car goes up and down on the road. What causes this?
    • A: When a strut pressure control valve gets ‘sticky’ due to scratches, wear, or dirt, the precision control spool can stick-slip instead of moving without friction in its bore. This can cause instability in the height control as the active system computer says ‘lower a bit’-and nothing happens, it say louder LOWER A BIT, then the spool slips—too far – and the car drops—and the cycle starts over. If the wear is bad enough, high pressure oil leaks past the spool into the strut and the control solenoid cannot stop the oil flow (the solenoid cannot exert less than zero force to release the excess pressure.) Correcting this required adjustment of the ‘balance spring’ on the offending valve spool. Contact B&B Suspension for advice.