I had a check engine light come on. The dealer advises the code it shows as PO153 and that both "HEGO" sensors have slow responce." Can anyone tell me what the "HEGO" sensors are; and where they are located? I have the Chiltons, but cannot find "HEGO: anywhere. Thank You !
1998 Explorer 4.0 SOHC
They are mounted in the exhaust system ahead of the catalytic converter.
P0153 is specific to bank 2 sensor 1. You cannot say that both sensors are slow from seeing just code P0153, though the dealer could have hooked up a tester and looked at the cross counts for both sensors. Perhaps they are both slow, but only bank 2 is over the P0153 limit.
If the Oxygen sensors have more than 75000 miles on them, I would change them both out. They cost about $50 each. If the oxygen sensors are nearly new, I would try to figure out which bank is "bank 2". One way to do this is to deliberately disconnect the harness to one of the sensors. That will post a fault code other than P0153, but similarly specific to one bank. From this you can determine which bank is which.