Hello, I have a 2010 Lexus GS450h. There’s a strange humming noise coming from the rear, along with a slight vibration when driving with low throttle or using cruise control at low speed. It feels like something is pressing against the rear wheels. The same noise occurs when going downhill without pressing the gas, but there’s no noise when in neutral. What could it be? If it were the drivetrain, it would probably make the noise even in neutral. I’m wondering if it might be the hybrid motor.
Mystike
Lexus MGR Diagnostic Simulator into a world-class, professional training tool Lexus GS450H Problem
Hello MystikeMysticism,
That’s an excellent and very detailed description of the problem. Providing the specific conditions when the noise occurs (low throttle, downhill regen) and when it doesn't (in neutral) is key to an accurate remote diagnosis. My name is Lakshan, and with over 14 years of experience in advanced diagnostics, particularly with Toyota and Lexus hybrid systems, I believe I can offer some insight.
Your initial diagnostic reasoning is spot on. The fact that the noise disappears when the car is in neutral correctly points away from standard drivetrain components like wheel bearings or the driveshaft, as these would typically make noise whenever the wheels are turning, regardless of the gear.
You are heading in the exact right direction by suspecting the hybrid system.
Primary Diagnosis: Rear Motor Generator (MGR) Bearing Failure
Based on the symptoms you've described, I am highly confident that the issue lies with the bearing(s) inside the Rear Motor Generator (MGR) assembly. Here’s why your description perfectly matches this diagnosis:
This is a high-voltage system and should only be inspected by a technician qualified to work on hybrid vehicles. Please share these steps with your trusted mechanic.
You've done excellent diagnostic work on your own. I hope this provides the confident answer you were looking for.
Best Regards,
Lakshan Hettiarachchi Founder, SL Trade Software Solutions Advanced Diagnostics & Vehicle Systems Specialist
plz find attach link
Hello MystikeMysticism,
That’s an excellent and very detailed description of the problem. Providing the specific conditions when the noise occurs (low throttle, downhill regen) and when it doesn't (in neutral) is key to an accurate remote diagnosis. My name is Lakshan, and with over 14 years of experience in advanced diagnostics, particularly with Toyota and Lexus hybrid systems, I believe I can offer some insight.
Your initial diagnostic reasoning is spot on. The fact that the noise disappears when the car is in neutral correctly points away from standard drivetrain components like wheel bearings or the driveshaft, as these would typically make noise whenever the wheels are turning, regardless of the gear.
You are heading in the exact right direction by suspecting the hybrid system.
Primary Diagnosis: Rear Motor Generator (MGR) Bearing Failure
Based on the symptoms you've described, I am highly confident that the issue lies with the bearing(s) inside the Rear Motor Generator (MGR) assembly. Here’s why your description perfectly matches this diagnosis:
- Noise under Load: The humming and vibration occur only when the MGR is under electrical load. This happens in two specific scenarios:
- Low Throttle/Low Speed Cruise: The GS450h uses the rear motor for gentle propulsion and to assist the main system, especially at low speeds. This puts a load on the MGR.
- Downhill without Gas: This is the most critical clue. When you are going downhill, the system enters regenerative braking mode. The rear wheels turn the MGR, which then acts as a generator to recharge the hybrid battery. This regenerative process also puts a significant electrical and magnetic load on the motor's internal components.
- Silence in Neutral: When you shift to neutral, the MGR is electrically disengaged from the drivetrain. It is no longer propelling the car or regenerating power. It's essentially free-spinning with no load, which is why a worn bearing would become silent.
- Drivetrain: As you correctly deduced, these parts would make noise based on wheel speed, not electrical load.
- Main Hybrid Transaxle (Front): While possible, the noise is distinctly coming from the rear, which isolates the problem to the rear-wheel-drive portion of the hybrid system.
This is a high-voltage system and should only be inspected by a technician qualified to work on hybrid vehicles. Please share these steps with your trusted mechanic.
- Safety First: Ensure the high-voltage system is properly disabled before any physical inspection of the drive unit.
- Stethoscope Test (On a Hoist): This is the definitive test. Raise the vehicle securely on a lift. Have someone inside 'drive' the car at the low speeds where the noise occurs. A technician can then use a mechanic's stethoscope to listen directly to the rear motor/differential housing. The humming/grinding noise from a failed bearing will be very obvious and easy to pinpoint with this method.
- Check Rear Drive Unit Fluid: Ask the technician to inspect the fluid in the rear differential/motor assembly. Any signs of metal shavings or a dark, burnt appearance would confirm internal mechanical wear.
- Scan for Codes: Even without a warning light, a professional scan tool (like Toyota Techstream) should be used to check the Hybrid Control ECU for any "shadow" or history codes related to the rear motor's performance or temperature.
You've done excellent diagnostic work on your own. I hope this provides the confident answer you were looking for.
Best Regards,
Lakshan Hettiarachchi Founder, SL Trade Software Solutions Advanced Diagnostics & Vehicle Systems Specialist
plz find attach link
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
