We bought our 2007 XK coupe in 2012. It had but 13K miles, and had spent most of its previous ownership garaged/short trips in Hilton Head, SC.

Soon thereafter it began emitting check engine light (CEL) with P00171 code, indicating a lean left bank condition. This CEL problem began slowly, maybe one a month at first. I have a code reader and cleared the codes. I expected the CEL would immediate reappear if this was persistent problem. It did not. Car ran great with no reduced performance.


My wife uses the XK as her daily driver – almost entirely short trips of less than 5 miles. About twice a month she drives 100 mile round trip. The CEL continued to light, about every three weeks now.

I replaced the mass airflow sensor (MAF) – but no changes. We took a couple of long trips and noted that the CEL was quiet throughout travel, but problem began again after about a month at home.

I wondered if this was an intake/exhaust leak that somehow closed up with heat expansion? Gradually, the CEL became a daily occurrence. Figured if it was just P00171 it would not be an intake tract, as usually both P00171 and P00174 should be triggered by an intake tract leak. By this time I had mounted a ScanGauge on my steering binnacle so as to more easily clear CEL. The CEL would light soon after the fuel system went to closed loop. About 1/3 of time both P00171 and P00174 would trigger. Once reset, it would not relight for the entire trip. Now the XK has over 32K miles.

Wondered if I had dirty/clogged injector(s). Added Techron with every oil change and in between. Car continued to run great – idle smooth and plenty of power throughout rpm range- no flat spots.


I completely disassembled the intake tract from air filter box to intake manifold checking for any leaks visible or not. Used a bit of silicon gasket sealer on reassembly. Even covered/sealed the accordion/bellows. Checked for leaks with a propane bottle – no rpm rise. Checked for visible exhaust leaks from underneath the car looking for any charring – found none. Considered about smoke testing intake and exhaust, but never got to it.

Searched this forum for answers. Posts seemed to indicate that Oxy sensors were never the issue. I knew that the car’s computer checks Oxy sensors at every start up, but wondered if the check was just a continuity check? Could there be something wrong/slow/fast with the timing of the Oxy sensor warm-up? I have a Jaguar CD manual and was unable to find a procedure for checking Oxy sensor internals.

Ordered Denso oxy sensors for the forward ports, and had them installed. No immediate joy as CEL returned as though programmed. Did a “hard reset”, which fully recognized the new oxy sensors. No more CEL and no more “pending codes” on ScanGauge. It’s been a couple of weeks now and no further CEL, so I am keeping my fingers crossed hoping that it is “job done”.


I have posted about this before, and thank all those who responded with helpful suggestions.

 

I would get the smoke test done before replacing any more parts.

 

Thanks. If that ever happens to me I will do a Hard Reset right out of the box. Maybe save me some time and frustration.