MPG Get Worse, Got Code 27 On Diagnostic

My 1995 XJ with inline six engine suddenly sucks more fuel than usual. My mileage get worse by almost 50%. I ran a diagnostic and it reads Code 27 (Fuel Injection Controller Circuit) and Code 17 (Speed Sensor).

Which code is more relevant to the MPG getting worse? The engine runs fine, engine check doesn't light up, everything else seems normal.

If it is the fuel injection controller circuit, what do I have to do to fix it?

Thanks folks.

code 17 should be coolent temp sensor, I would start there.

Engine did not reach operating temperature within acceptable limits. Engine does not reach 20º F. within 5 minutes with a vehicle speed signal. Code 17

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Yep, the code 17 was mystiped. It should be code 15. Thanks for correction. So any clue for the code 27 fixing?

Fix the speed sensor first.

Okay, I will fix the speed sensor first. Please tell me, before I start working on it, does it usually need replacement or cleaning would do? I would rather prepare the parts first if replacement is normally required.

How does the speed sensor affects mileage anyway? Oh yes, my speedo looks normal, no jumping nor dead.

Thanks again John, let you know the result. :repair: