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Pete, Technician
Category: Lexus
Satisfied Customers: 24142
Experience:  Over 17 years diagnosing and repairing automobiles various makes and models with some training and certifications.
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Transmission makes a whining sound only in gear either

Customer Question

Transmission makes a whining sound only in gear either reverse or drive. There is no whining sound in park or neutral. Considering those two symptoms, if I change the torque converter will the whining sound go away? Is the whining sound an indication of a bad torque converter. // Second question - check engine light comes on periodically. I pulled the code and it is PO420. Sometimes the check engine light turns off by itself. Is the PO420 an indication of bad catalytic converter or bad oxygen sensors. My gs300 has approximately 215,000 miles and I am the original owner.
Submitted: 5 months ago.
Category: Lexus
Expert:  Pete replied 5 months ago.
Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay. The whining sound can be an indication of the transmission fluid pump itself at fault needing replaced or an issue with the torque converter.This would have to be inspected further to locate the source of the fault and then from there repaired to correct this issue.Both require the transmission to be removed to replace so the transmission will have to be removed for inspection and repair.The code you have here is for a restricted catalytic converter needing replaced.The only other things that can cause this code is an exhaust leak or after market or damaged exhaust components.It is possible one or more oxygen sensors need replaced but most of the time it is the catalytic converter itself that needs replaced. If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.Thanks Pete
Customer: replied 5 months ago.
Thanks for the response. As for the transmission whining sound, wouldn't the sound occur even when the transmission is in park and neutral in addition to drive? I was going to go ahead and change the torque converter, but wanted to get a second opinion before investing time and money in doing so. It doesn't make sense to me that the whining sound only occurs when the torque converter locks up in drive and the whining sound stops when the torque converter is not locked-up in park and neutral.
Expert:  Pete replied 5 months ago.
Usually if the sound is not there in park or neutral this can indicate a fault with the torque converter itself as it is free wheeling when in park and neutral and is engaged/operated when in drive or any other gear.I would lean on the torque converter itself as the cause here needing replaced with all that is described here.It may be a good idea though to have the entire transmission checked over to make sure no other faults are found with it when this repair is done. Let me know if you need anything else and feel free to rate my help here. Thanks Pete

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