Earlier this year my wife's car had a bad head gasket, which was taken care of and now the car seems to be running fine. Now, however, the light came back on and I can't figure out why. I do know that the exhaust manifold has a crack in it, but I don't know if that would cause a lack of backpressure that would cause a light to come on. Coolant levels are fine and the car runs normally; no colored smoke or funny smells either. I popped the gas cap and reseated it, then reset the light using the 7.5A option fuse under the hood. However, the light came on again this morning.

 

Well have you tried pulling the codes?

 

A cracked manifold is likely to cause O2 sensor or improper mixture codes. Air comes in through the crack and fools the O2 sensor because of the extra oxygen.

But that's purely a guess until you pull the code. It could be something completely unrelated.

 

Code should be pulled today. mk378, I was thinking bad O2 sensor possibly, but that's more likely given the circumstances.

 

Got a code today. It came up P1336, intermittant sensor interruption. I take that to mean the O2 sensor it not happy with the cracked manifold. What I want to know is, what kind of damage am I looking at if I don't get that repaired immediately. I'm strapped right now and while I will get around to getting it fixed, the wheel bearing on my own car is a little more important (it's getting LOUD).

 

That's a code for the CKF (crankshaft fluctuation sensor) located behind the lower timing belt cover. The CKF sensor wires exit the upper timing belt cover. Follow them to the connector to make sure its plugged in. Otherwise, the wires may be damaged behind the timing belt cover. This probably happened because the sensor was not reinstalled correctly after the head/timing belt job.