Hydraulic Hiss or Moan Noise Under Brake Torque Conditions - keywords 4L85E automatic groan growl MN8 vibration
| Subject: | Hydraulic Hiss or Moan Noise Under Brake Torque Conditions |
| Models: | 2002-2005 Chevrolet Suburban and Avalanche |
| 2002-2005 GMC Sierra and Yukon XL |
| Equipped with 4L85E (RPO - MN8) Automatic Transmission |
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Hydraulic hiss or moan noise under brake torque conditions on vehicles equipped with a 4L85E (RPO MN8) automatic transmission. Noise may be present at very low speeds, below 3 mph (5 kph).
Recommendation/Instructions:
The cause of this hiss noise is transmission fluid being forced from the front pump under high velocity and high pressure, under brake torque conditions. This noise is considered normal, and is a characteristic of fluid flow through the torque converter that is used with the 8.1L engine. This noise does not indicate a reliability or durability issue. However, the action of brake torquing (applying the throttle while holding the vehicle in place with the brake) is not a recommended practice. Doing so for more than 15 seconds within a ten minute time period can overheat the transmission fluid, and damage components within the transmission.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
