STEP 4: Checking For Trouble Codes
Whenever I'm diagnosing a no-start condition, I don't usually check for trouble codes since most engine no-start problems don't usually leave a trouble code.
But in this case, I ended up hooking up my generic scan tool because all my test results pointed to a bad crankshaft position (CKP) sensor and I wanted to know if there was a crankshaft position sensor trouble code stored in the fuel injection computer's memory.
To my surprise, there was a camshaft position (CMP) sensor trouble code instead of a crankshaft position (CKP) sensor trouble code. It was an OBD II P0340 trouble code.
My next step was to check the camshaft and crankshaft position sensors, but at this particular point I didn't have the required wiring diagram.
So I told my friends that I would have to run to a friend's auto repair shop to get the wiring diagram to test the CMP and CKP sensors and that meant I would come back the next day.
STEP 5: Testing The CMP And CKP Sensors
Since my previous tests had confirmed that the ignition coils were not firing spark and the fuel injectors were not receiving their trigger (activation) signals, it became fairly obvious to me that the CKP sensor was faulty.
Why? Because previous experience has shown me that if the crankshaft position sensor fails, the fuel injection computer will not activate the ignition coils or the injectors.
It has also been my experience that if the fuel injection computer registers a CMP or CKP sensor trouble code, you need to test both.
There have been times when I've gotten a CMP sensor trouble code and it turned out to be a failed CKP sensor (and vice versa). So I've made a habit of testing them both to make sure I'm replacing the one that's bad and causing the problem.
On the 2002 1.8L Nissan Sentra, testing the crankshaft and camshaft position sensors is fairly easy. The only tricky part is accessing the crankshaft position sensor as you have to remove the air cleaner assembly from the engine to access the connector from the top of the engine.
To test the camshaft and crankshaft position sensors, I followed the instructions in these two tutorials:
- How To Test The Camshaft Position Sensor (2000-2002 1.8L Nissan Sentra).
- How To Test The Crankshaft Position Sensor (2000-2002 1.8L Nissan Sentra).
Well it turns out the fuel injection computer was right all along as my tests confirmed the camshaft position sensor was stuck producing 9 Volts DC and never switching the signal down to 0 volts.
I ran down to the auto parts store and bought the camshaft position sensor, came back and replaced it and the engine started!
My friends were pretty happy! And so was I, since I dodged a bullet (by not having to replace the fuel pump).
More 1.8L Nissan Sentra Tutorials
You can find a complete list of tutorials for your 1.8L Nissan Sentra here:
Here's a small sample of the tutorials you'll find in the index:
- How To Test For A Blown Head Gasket (2000-2006 1.8L Nissan Sentra).
- How To Test The Starter Motor (2000-2002 1.8L Nissan Sentra).
- How To Test Engine Compression (2000-2006 1.8L Nissan Sentra).
- How To Test The 2000-2002 Nissan Sentra 1.8L MAF Sensor (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!