P0340 Camshaft Sensor Opel Astra H

Hello gents. Having a problem with my car. 2008 Opel Astra 4 Cyl Petrol. Im in need of help to properly diagnose a code that is popping up in the scan tool.

P0340 Camshaft Position Sensor, the code does not turn on the Check Engine Light (the light works and test correct) but the scan tool shows it as Present, once I clear the code, every time I start the car, the code appears again in the scan.

The car randomly starts very rough, at very low rpm (500 RPM aprox) and after a few seconds then stabilizes at 800 RPM also it feels a bit lacking in power, and the exhaust stinks of gas. Either cold or hot. Also if the car stalls for some reason, it takes a long cranking time to start (about 5 seconds)

Also in other occasions (I would say 25% of the time) the car starts smooth and goes to 1200 RPM (when cold) and slowly goes back to 800 RPM.
When this happens, the car feels more torquier and pulls better.

Camshaft Position Sensor is a 3 wire Pull Down sensor. Im adding electrical diagram:

I back probed the 3 wires with the scope with the connector plugged and unplugged, with Ignition on and off.

Ignition Off - Connector Plugged / Unplugged is the same.

1 - Ground 25 Ohm to Battery Ground
2 - Signal 1V (isnt this weird?)
3 - Reference 0V

Ignition On - Connector Unplugged

1 - Ground 80 Ohm to Battery Ground
2 - Signal 12V (when plugged sometimes its 0V, others 12V, I guess from the camshaft being in position)
3 - Reference 5V

This is the signal with the car running 1 is signal and 2 is 5V reference.

The camshaft has only one somewhat big protruding chunk of metal that triggers the cam sensor.

Cam sensor is pretty expensive (about 200 USD) so i would rather not just buy a new one for trying, also sensor seems alright. What I dont understand is why signal is 12V when reference is 5? Shouldnt be signal 5V when reference is 5V? Also what about that 1V in the signal wire when ignition is off?

Please let me know your ideas about this issue, also any other troubleshooting ideas would be nice.

What is voltage on the ground wire, ignition on, plugged in?

What is voltage on signal wire, ignition on, unplugged?

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Thanks for your response, somewhat i forgot to add that information that I already had.

Voltage on the ground wire, ignition on, plugged in is: 0.0014 V

Voltage on signal wire, ignition on, unplugged is 12V or whatever voltage is the battery sending, could be 11, also when the car is running, signal goes between 0 and 14,2 that is what the alternator is generating, for instance, everytime i say 12V, i mean battery voltage.

Dont know if I made myself clear or made it worse. Any help is appreciated. Thanks

When checking the sensor reading should be done while cranking the engine. 100mv on the ground, 5v on ref and 5v on sig, however some have a 12v sig and they are mostly pull-up design. Running readings will be slightly higher. That said, scope looks ok but I can't make out voltages. I would check sensor air gap and relucter ring.

Hi ScannerJohn, i dont know if I fully understood you, you want me to record with the scope while cranking the engine but not starting it?

The voltages you see on the scope image are 0 to 14V for the Channel 1, that is connected to signal, and constant 5V for channel 2, that is reference.

In the software different channels are not to scale.

Regarding air gap, sensor is not adjustable, just a fixed bolt to engine head. Does that help?

To test the sensor, it's correct to test by cranking the engine not starting it. Use your multimeter. Neg to battery ground. Back probe wires at connector. Ground reading should be around 100mv. Sig and ref in your case, 12v and 5v. When checking the pull-up or pulldown square wave the only way is with scope while engine running. DMM to slow to give accurate readings.

Intermittent problems are hard to pin down. Have to catch it when acting up. If cam sensor is good check crank sensor as well. Same test procedure.

Check the physical condition if the cam sensor and relucter.

I keep coming back to the same conclusion that the air gap is off... I found this fix from a Opal Astra owner with the same problem. He solved it by modifying the sensor housing so the sensor sits correctly.
www.astraownersnetwork.co.uk/threads/cam...0.74566/post-1128008

Let us know if it solved the problem.

Hi guys, thanks for the feedback im sorry for not being able to update this topic, its been very cold and rainy the days I had to work in the car, and the only place i have to work is the roofless driveway so a bit hard to do much. I tested the sensor while cranking the engine, the graph is just the same as the one posted above, only difference is that first "waves" are to 0-11v aprox (i guess because starter is choking all the battery power) as soon as the car starts it goes normal.

I also tried simply disconnecting the sensor and starting the car. It started with no difference as to when the sensor is connected and threw the same code. Im already waiting on a new cam sensor to arrive, ordered it overseas to save quite a lot of bucks. So I will update when it arrives. But i dont feel it would solve the problem. Maybe ECU?

Regarding air gap, thats a very different engine albeit the same car (thats a 16v versus an 8v on mine). This sensor doesnt have wiggle room, if the air gap is off, probably is time for a new camshaft. I removed it and placed it in place again, no wiggle room.