Lexus GS450h Owner's Manual page 569

Start the hybrid system and check for the multi-information display.
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If the message does not disappear:
Stop the hybrid system and contact your Lexus dealer.
If the message is not displayed:
Have the vehicle inspected at the nearest Lexus dealer.
When adding coolant
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Add coolant in accordance with the following procedure.
Remove caps A and B.
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Add coolant through the inlet of cap A up to the B-line, and then
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install cap A.
Add coolant through the inlet of cap B until it is full, and then install
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cap B.
Cap A
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Cap B
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B-line (Target fill line)
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GS450h_OM_OM30E26U_(U)
7-2. Steps to take in an emergency
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