The problem I see on a lot of forums such as this is that the owner wants to repair the vehicle on the cheap and avoid the garage bills and I understand this.
I also see people with code readers retrieving a fault code and then go straight for a component change. This is where the untrained enter the minefield of repair by substitution of components which inevitably ends up being more expensive than a trip to a garage.
In the world of diagnostics technician's are trained to treat the fault code as a symptom and not the cause. The DTC P0171 "System too lean" is a classic for which I have seen the O2 sensor, MAP/MAF, fuel filter and fuel pump changed to name but a few and the fault remain only to find the fault was a simple vacuum leak.
If you have a decent DVM that has frequency or duty cycle on it you can test if the CMP is producing a signal. The testing should be done at the ECU end and not the sensor.
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