2004 Chevy Trailblazer 4.2L check engine light.
How to replace cam and crankshaft position sensors?
The crank position sensor is located on the drivers side of the engine, along with a few either sensors. You can either jack up the truck and take the drivers side wheel off to access the sensor. It is actually easier to get to it from under the truck. It is just bolted on with one 10mm bolt.

The cam actuator solenoid is located on the passenger side front of the engine, These are common to fail and cause a check engine light code P0014 or P0016. When they fail, it causes a correlation code between it and the crank sensor. To remove the cam actuator solenoid, you will have to remove the drive belt and the either remove the power steering pump, or at least loosen it enough to slide it out of the way far enough for the cam sensor to clear the steering pump cap. Then it is just a 10mm bolt that holds it in. Wiggle it and slide it out, then install the new one.
After these repair, a "Cam / Crank correlation relearn" will need to be done. A high quality scan tool will be needed to do this properly. Some people have other ways to do it like letting it idle for a few minutes, or driving on the highway for 10 miles, but none of these work.

If you do not do that relearn, the engine light will come on and you will have codes. This could look like the parts did not fix the problem, when they actually did.
Replacing Chevy Trailblazer Cam And Crank Sensors
Chevy Trailblazer Crank Position Sensor
Cam Solenoid
Crank Position Sensor
Chevy Trailblazer Cam Actuator Solenoid

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