Check Engine Light

I have a 2004 Subaru Outback, 4 cyl. 2.5L engine. The check engine is driving me nuts. It came on last spring, went off in a couple of days, came on again, etc. After 4 cycles of this, my mechanic checked the codes and determined the rear O2 sensor needed replacement, which it was. The light still comes on, then goes off (takes about 500 for it to cycle off). My mechanic has checked the codes when the light is on. All reading nominal! He clears the codes. Best he can figure is gas formulation. The nuisance is when check engine light is on, cruise control does not work.

Any suggestions?i

All reading nominal! He clears the codes.

These sentences contradict each other, and if the “Check Engine” light is on, the second is true. His “best figuring” (gas formulation) doesn’t add up. Go to AutoZone or a similar chain auto parts store and a free reading of diagnostic trouble codes. Post the exact results here.

What is the code? If the cruise control isn’t working, that points to the VSS (Vehicle Speed Sensor) signal not reaching the engine computer.

If the ECM is not storing codes, is the car ‘emissions ready’? This is easy to check with a code reader or scan tool. If the scan tool reads clear, but not ‘emissions ready’, then there is an electrical problem causing the ECM to continuously reset itself. Many of the emissions checks built into the ODB-II system requires certain driving conditions be met and tested to be ‘emissions ready’. If the ECM never reaches that point due to reseting, then that is also a problem. Have all the fuses checked first. Then, you may need to see an auto electrician if the fuses all check out.

Hi megibbons1065,
This may sound silly…but my 1996 Dodge Dakota with 230,000 miles just popped the dreaded light on, the night after I had bought new plugs and wires and promised her a tune-up that morning. But life being what it is, mu mechanie was slammed, so I drove 120 miles to see a girl friend and en route the light popped on for the first time ever. I figure my Dakota was pissed at me for not honoring my promise. Did you promise your Outback something (verbally, outloud) that you didn’t honor??? I know it sounds silly. But for me, my Dakota has been 100% silent all these years… and I’ve always previously honored my promised.
from Dakota.Blue