My son and I have almost the same car,mine is a 98 Honda civic and his a 96 civic?

Question

my engine light went on and he found that I had a cracked manifold. He switched them in the cars. My light doesn't go on anymore and he fixed the problem. The question is, why doesn't his engine light go on with the cracked manifold?

Answer 1

Need to be a little more specific.
Intake manifold or exhaust manifold?

If it's an exhaust manifold, his O2 sensor may not have yet detected the fault, or it has and it's trying to compensate with more fuel. Ask him how his fuel economy has been since the swap.

I got your message that it was the intake manifold that was swapped. With an intake manifold leak, you typically will suck in more air which was not read by the MAP sensor, thus resulting in more air in the chamber than fuel. Typically resulting in a lean burn, where there is not enough fuel. Not sure why the O2 sensor has not registered the problem, but usually using a cracked intake manifold will cause the exhaust valves to burn out.

Answer 2

He disconnected or bypassed the sensor?