In an earlier post tech asked if the 2001 S40 had a updated wiring harness. Is there such a thing???

 

What did I have it in reference to?

 

Original post: s40 2001 check engine code points to slow response from oxygen sensor #1. After dealer service dept. replaced and replaced again, still causes check engine light with same code after a hour of driving. What to do now?

Techs answer: Has the updated wiring harness been installed? Does your car have the latest softwara downloaded into it?If not have that done and that might take care of the problem.

I feel I have a slight hesitation in my 2001 S40. I have new Volvo plugs & air filter. Also new coolant sensor & MAP sensor. And I saw your post using the word "updated" and thought I might have missed something. By the way where is my fuel filter located???

 

Your fuel filter is located under the L/S of the car by the back tire. It is under the black cover.
Does the hesitation happen under acceleration?
If so have you changed the coils yet?

The harness goes inline for the front O2 sensor. But that is usually installed for a Code problem.

 

Havent changed the coils yet. At 74,000 it might be time. The hesitation is when I accelerate and then it takes off.

 

It might be a coil missfiring Intermit. or maybe something else.
Does the check engine light flash or come on?

 

No check engine light.

 

Considering the milage you might want to replace the coils and see from there.