Engine light on after head gasket repair

I need some help. I recently got my head gasket replaced on my 02 nissan sentra since I was loosing coolant. After the job was done the mechanic said the service engine light came on with an error code p0335 ( crank shaft sensor ). Even after replacing the timing sensor and the crankshaft sensor the engine light is still on. What should I do ? It is definitely something went wrong when the head gasket was being replaced . Any ideas what may be wrong?

First how long has it been since the repair. Some times it takes a while for the error code to be turned off.

Second I would get the code read to make sure it is the same code. It may not be another P0335.

Last, error codes do not say “replace crank shaft sensor.” What they may say is Hey guy, I am seeing some sort of odd report from something around the crank shaft sensor. It may mean you need a new crank shaft sensor, or it may mean something else is messing with whatever senses a problem with the crankshaft sensor. Those computers are really nice to have, but they don’t replace the old way of looking for a problem.

It happened immediately after the repair. The error code is P0335 even after replacing the sensors. I made sure of that. The car drives fine but wont be able to pass smog. The sensor is detecting some problem but I have no idea what it is suppose to sense.

D?j? Vu All Over, Again?

What makes you think its a bad ECM ?

Your tech will have to use a oscilloscope to check the sensor and if all checks out ok, check the signal at the pcm. If all is ok, check all pcm grounds and if all is ok it is a case of faulty PCM. Do not skip tests and go replacing parts, too much $. He needs to make sure there is a base voltage to the sensor and that is producing a signal with the key on, engine off and with the engine cranking. Remember that the base voltage is shared with other sensors and the ground must be present at the sensor. Good luck.