Yesterday while driving back home, my “CHECK ENGINE” light comes on, we run the scanner, and the code is:

P0133: O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)

the O2 sensors are new, the harnesses are intact, and there are no vacuum leaks. What could be causing this code? Thank you.

 

What brand sensor?

 

Unbranded eBay sensors. I just bought Densos. Are they good? Is it true that NTK is are the stock manufacturers?

 

NTK and Denso are both OEM suppliers. Putting in a good one will likely solve your problem. These trucks are notoriously picky about what sensors they will play with.