I recently purchased my 2003 S-type, V-6, 5 speed manual with 70000 miles. Great car, but I immediately had some issues. The a/c was randomly blowing hot air, I was getting an engine light with a P0174 code, there was an oil leak at the rear of the engine, there was a slight coolant leak, and it needed shocks. I researched this forum and found answers and suggestions for all. I replaced the shocks, DCCV, coolant overflow reservoir, and fuel trim o-rings. Solved all problems except the engine light and P0174 code. I checked all vacuum hoses and connections visibly and by spraying carb cleaner and watching for rpm increase. No success. I read a post that suggested it might be a weak battery. I checked voltage across the battery when engine was off and found 11.9 volts. A little weak, but how could this cause the P0174 (right bank lean) readout? I replaced the battery anyway. Now, I have 12.8 v across the battery. I've driven the car 400 miles and no engine fault lights. Thanks for all of the excellent advice I received on this forum. I really like the car.

 

I think with weak battery you can get poor (or even intermittently no) spark as the coil can't get peak energy. Thus misfires and code(s).

 

Glad to hear that the forum resolved all your problems. This forum remains by far the best tool in our toolboxes. I wouldn't even attempt to keep our two Jaguars without access to it....

 

Those vacuum leaks are very hard to find. I followed JagV8's suggestion and monitored the short and long term fuel trims real time while I sprayed carb cleaner at area's I thought might leak. I found it was the vacuum connection to the intake manifold for my P/B booster.


The engine just adjusts so fast you can't really feel anything when testing it and the fuel trims are VERY sensitive. So they show even the smallest vacuum leak.
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