ASE A4 Suspension and SteeringSuspension System Diagnosis and RepairHard
A vehicle with an active suspension system that uses continuously variable dampers is diagnosed with a persistent knocking noise from the left front when driving over small bumps. The technician observes that the noise is consistent and not related to steering input. No diagnostic trouble codes are present. Which of the following is the MOST likely cause of the knocking noise?
- AInternal damper failure.
- BWorn upper strut mount bearing.
- CLoose damper shaft nut.
- DFaulty ride height sensor.
Show answer & explanationAnswer & explanation
Correct answer: A. Internal damper failure.
A persistent knocking noise over small bumps, unrelated to steering, with no DTCs, and in an active damper, strongly points to an internal damper failure. Active dampers can still fail mechanically (e.g., worn internal valves, gas charge loss) even if their electronic control is functioning and not triggering codes.
Why the other options are wrong
- B. A worn upper strut mount bearing typically causes a clunking or popping noise when turning the steering wheel, or a 'twang' noise, not usually a consistent knock over small bumps unrelated to steering.
- C. A loose damper shaft nut would likely cause a more pronounced clunk or rattle, and if severe, could lead to significant damage, but 'knocking' often points to internal issues.
- D. A faulty ride height sensor would cause incorrect leveling or DTCs, not a mechanical knocking noise.
Internal Damper Failure Noise
Internal mechanical failures within a shock absorber or strut, such as worn valves or loss of gas charge, can produce a consistent knocking or rattling noise, especially over small bumps.
- Can occur in active or passive dampers
- Causes knocking/rattling over bumps
- Often no DTCs for active systems
Memory trick: Knocking over bumps, no codes, no turns? The damper's insides are having burning concerns!