2001 GMC C2500 • V8 2WD Automatic • 158,000 miles

2001 GMC 2500 has "service engine" in message center
local oil change shop says error messages indicate problem with O2 sensor and anti-knock sensor. They recommend replacing all 4 O2 sensors but told me to take truck to someone who works on engines to fix antiknock sensor. Their part will cost $569. And said other sensor replacement may be double that. I will do it if necessary. What do you recommend?
December 14, 2010.

First, the O2 codes should indicate which sensor is bad. You shouldn't have to replace all of them. The chances of all of them going bad is very odd. Next, I believe they are refering to the knock sensor. That, itself, could cause the O2 sensors to show bad readings because the knock sensor plays with ignition timing.

I agree with him. Have it checked by a different shop. I don't feel you need all the work they are requesting.