Having troubles isolating the cause of a recurring P0171 lean left bank
code. Noticed a leak in the fill reservoir today.

I know this may be a stretch, but, I'm at my wit's end trying to fix this
code problem.

I've read that a bad oxygen sensor may cause this to pop up. But, don't
the oxygen sensors have their own code if they are malfunctioning?

Thanks for your help.. Ed

 

I would not think a leaking coolant reservoir would be the cause of a P0171 code.

Remember that a P0171 code is for Bank 1 only so that would narrow down the problem to one side. For that reason I would suggest it is related to a fuel presentation “fuel injectors” , exhaust leak before the catalyst or a problem with the O2 sensor. Yes the O2 sensors can be related to many other issues that key up different codes. If it were me I would add BG44K to your fuel and see what takes place.

Codes are a tool to aid you in determining what has gone wrong they to not tell you what is wrong just what it is not doing correctly.

 

My code 171 was the mafs. Sprayed with cleaner and no help. Looked at it with jewelers loupe and it was a little dirty. Cleaned with Q-tips wet with cleaner and problem solved. Be very, very careful, they are delicate