My car has 77000 miles.
My car has an automatic transmission.
Hello. Code P0599 is the code for an issue with the thermostat heater control circuit, while P0171 is for a lean condition on bank 1. P0599 is set when the computer detects that there is an issue with the electronically regulated thermostat's circuit. It may be possible that the electronic thermostat has failed and needs to be replaced. P0599 is set when the computer detects a lean condition from the engine. A lean condition can be caused by many things. A few common causes are a faulty fuel pump, fuel injectors, or oxygen sensor. I would start by taking care of the thermostat issue, as thermostat issues can sometimes lead to overheating, and then move to the oxygen sensor. If the oxygen sensor has been cleaned, then it may be possible that it is faulty and needs to be replaced, or that the issue is elsewhere. If you would like, a certified technician from YourMechanic can perform an Check Engine Light inspection, and make necessary repairs.
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