1997 Jaguar XJR Engine light

  • 1997 JAGUAR XJR
  • V6
  • 85,000 MILES
My car has given me no problems as I've neglected to take care of it. Haven't had an oil change or tune up in 2 years. Engine light on, coolant light on, oil light on. 2 weeks ago the mechanic did a diagnostic cuz it wouldn't start and read only one code po 411 secondary air injection system incorrect flow detected. The mechanic said the was a tube (not exact terminology he used) connected the engine looked very loose he tightened it and said it had to be connected air tight in order to build compression to get the car to start up. Since that cars been a ok but I wanna find out why the check engine light is on. Any ideas?
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Tuesday, February 18th, 2014 AT 8:54 PM

1 Reply

The Engine Computer detected a problem, set a diagnostic fault code, and turned the light on to tell you. If your mechanic erased the codes after the recent service, and the light turned on again, there is a different problem now.

The computer looks at a lot of sensor readings and operating conditions, and compares them to each other to determine when there's a problem. One of the conditions to set a code is that certain other codes can't already be set. If those original codes relate to something the computer uses for comparison, it knows it can't rely on those readings, so it will suspend some of those tests. Once the original problem is fixed, those tests resume, and that's when the new problems are detected. This commonly happens when problems are ignored. That gives new problems more time to occur but go undetected.

The common misconception is the mechanic is incompetent, but in reality he had no way of knowing there were other problems. Some tests only run at very specific times or under a specific set of conditions, so the new codes may not set for miles or days.

The place to start is by having the codes read again to see what is causing the problem.
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Tuesday, February 18th, 2014 AT 9:25 PM

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