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Won’t Start, Check Hybrid System and Check VSC System

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I have a 2008 Lexus 400h with around 113,000 miles on it.  A few nights ago it refused to start, saying "Check Hybrid System".  Full power to the lights and the dash, just no actual engine start.  When I went into the storage well in back to get my tools, I found moisture in the storage well under the matting over to the right, closest to the right rear tail light assembly.  I could not see where it might have come from.  I got a ride home from a family member.

I did a little research and went back to it the following day morning, pulled the battery terminals, waited ten minutes, and tried again.  This time it started and drove fine, with the hybrid system itself seeming to work, but I had no cruise control, no control of passenger windows from the driver's seat (the window switches at the actual window worked fine), and the traction control error light was on.  I used my BlueDriver to pull codes.  I have one Motor Generator Code, P0AA6, "Hybrid/EV Battery Voltage System Isolation Fault".  I also have 2 Antilock Brake System Codes, C1231, "Low or High Power Supply Voltage", and C1310.  Since then, in order to start it I have to pull the battery terminal and wait a few minutes.  It takes longer than usual to start the internal combustion engine, but when it starts there are usually no error codes.  Then, somewhere between one and twenty minutes, I lose cruise control and the traction control error light comes on.

This morning I pulled all the fuses related to the hybrid system.  They were all intact.

Any thoughts?  Thanks very much.


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I wonder if the traction battery or a related component is going bad.  I assume the traction battery is used to start the internal combustion engine of the RX400h like it is on other hybrid vehicles made by Toyota.

And how old is the regular 12V battery?  Does it test OK?  Even through it isn't used to start the internal combustion engine, it's critical in powering the vehicle's electric infrastructure ... gauges, audio system, accessories, etc.

I doubt if the brake code has anything to do with the problem.  Sometimes meaningful codes trigger others that aren't.

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  • 2 weeks later...

I agree. The key here is the age of your 12V battery. When ours is getting weak, we usually see a message that includes mention of the shifter not being in the Park position. I would guess that your battery is weak and needs to be replaced. It could also be that a cell or two in that battery is dry. This can also cause weird things to happen.

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  • 1 year later...

I have a 2 months old regular 12 V battery, but the same thing happened with my Lexus400h (TCGrace)

Check system, check hybrid system, check vsc system, check system etc. so I'm !Removed! off and regret to buy this POS.

I had a wonderful Nissan Altima 2003 brand new when we've purchased it. Just gave it to a friend with 288,000 miles still running well and never ever had to do anything with that great car, only change the oil, oil and air filter...

Lexus my A....

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  • 6 months later...

Note to everyone: You should have the codes read before jumping to any conclusions. If you do not have a code reader, take your vehicle to an auto parts store and ask if they will read them for you. 


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