S Type Bank 1 too lean
 

I have a 2003 S Type R. Fault code is P0171, bank 1 too lean. The "reduced performance" signal comes and goes intermittently. I am guessing an air filter, MAF or vacuum leak issue would also yield a P0174 for bank 2 as well. I am thinking a bad O2 sensor, does that sound reasonable? (I would think that would be a code as well). I seem to recall a couple of years ago the car was scanned and there was some issue with O2. I think bank 1 is passenger side-correct? Also, is it hard to change that sensor, any guidance in that regard is welcome....

Fred Emmerich

Do you have a way to read fuel trims and also the O2 sensor values. That would help immensely

+1 read fuel trims - much cheaper than parts-swapping and much more likely to provide some useful data.

Hot engine, parked. At idle, then rev to about 2500.

Check the PCV mount and hose to the throttle body for cracking.

You know who I learned the value of fuel trims from right jagv8....a hint....username is in this post

Not sure, I have a simple bluetooth reader.

What software are you using, it should probably be able to see fuel trims.

Torque Pro

Bank 1 LT = 18.8 ST = 0.8%
Bank 2 LT = 14.8% ST = 3.1%

I have seen where you want the short term to be around zero, and LT a bit higher. I am not sure what LT should be though.

Read them with hot engine, parked.

At idle, then rev to about 2500 and read again.

ST should be small and can usually be ignored. LT should be within (say) 5 of 0.

We can see your LTFTs are big. If they drop when revved you have an air leak... but do they?

LT for both banks is 17.2 at idle, drops to 14 at 2500RPM. ST stays the same, around 0-3%

I cleaned the MAF sensor and air filter, idle is now 16 (down from 17.2) for LT and 3 (up from 1) for ST. No check engine light yet.

That's hardly any drop so you're probably looking at something other than an air leak.

That leaves the rest of the list in the workshop manual / codes PDF. Free to download off this site or JagRepair.com - Jaguar Repair Information Resource

I'd clean the MAF (with great care) and if not recently done change the fuel filter.