Hi,

I just had my Check Engine Light turn on this afternoon. I have a '91 LS400 w/ just about 230K. I ran the CEL test, and it read code 21. What does this mean. I did a search and found something that mentioned the "solar sensor". What exactly is the issue and how would I fix this. Thanks in advance for the help.

 

Actually that code is for an O2 sensor.

You'll need to be replacing at least one of them.

 

Thanks for the response. How do I verify which o2 sensor it is... bank 1 or 2, upstream/downstream?

 

anyone have any ideas?

 

I think that specific diagnosis might require a code reader.

 

With your mileage, and if they are original, I would suspect both upstream.