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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.

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