2011 Subaru Forester xt CMP waveform questions

Hello all,    
so I have a 2011 Subaru Forester xt in with what a believe is jumped time, but I'm not sure.im still new to scope usage but hoping to get more confident. I've got p0301-p0304 and p0340 CMP sensor code. When I use the scope to get a waveform. It looks off from the service data example I have. Any info/ help would be greatly appreciated.

That's strange that they both go below Ov, looking at the sample waveform, these appear to be 3 wire all sensors?
The scope is set to 50v scale, that's too much. I would probably go 10v considering we're expecting a 5v square wave.
Also, exactly what channel is what sensor? Are these intake cams on opposite banks, intake and exhaust on the same bank etc.

Yes 3 wire hall effect on opposite intake cams.
When I set the verus to 5v 50ms per division it shows 50v for some reason. As far as the going below 0v I figure I had a trigger set wrong. Or could a shared scope ground be causing feed back?
Yellow is right hand and green is left hand. So I would think if the timing was correct it should look like the sample from service data.

I would think if the timing was correct it should look like the sample from service data.

Agreed, however the signal is not being acquired properly.
Misaligned cam timing will result in misaligned waveforms, not completely unexpected voltage levels in the waveforms.
When you have 0v to 5v square wave patterns on the screen, you can compare them to the known good.
Otherwise there is a signal acquisition error using the scope, or something strange happening to cam signal circuits.

I'll check again, I thought I was getting some kind of back feed because the negative wave matched up perfectly with the other trace positive.
Thank you Noah for your time and experience.

That's a crazy hall effect pattern!

could a shared scope ground be causing feed back?

I thought I was getting some kind of back feed because the negative wave matched up perfectly with the other trace positive.

My first thought was a bad scope ground. The two channels look, incredibly, clean to be missing a ground, though...?

When I set the verus to 5v 50ms per division it shows 50v for some reason

Could there be something wrong with your scope? Do you have another hall effect sensor, or different vehicle, available to test?




 

Possibly something wrong with leads, probably just my lack of familiarity with capturing waveforms. My yellow lead has a ground on both ends the green lead on has a ground on one end. So I back probed yellow into pin 24, ground from yellow lead into pin 30 (ground),and green lead into pin 16 with the lead ground on meter side going thru yellow lead pass thru ground.

Jostr wrote:

ground from yellow lead into pin 30 (ground)
 

Move this to the negative battery post.

All 4 channels of the (Verus) scope share a common ground. If you use the black connectors, of the yellow test leads, to ground the scope to the negative battery post, all 4 channels will be referenced to Battery Negative.  Always, reference (ground) the scope to the negative battery post.

Looking the waveforms, the wiring diagram, and the way you had your scope referenced to the sensor ground, I suspect you may have an open in the sensor ground circuit, from the computer ---> to the sensors.

To check the sensor grounds, open up another scope channel and connect it to a sensor ground, at the sensor. Voltage on the sensor ground should be less than 100 mV. If you are getting a square wave with an amplitude of more than 100 mV, then you have a bad sensor ground.

Thanks Chad I'll give that a shot. I appreciate it

Alright I think I fixed the scope usage problem (ME) here are updated screenshot 0-5v green trace still looks ahead of Yellow. Im going to pull the timing covers and check alignment of timing marks.

Nice capture, well done.
Certainly looks to be out of time to me when compared to the known good example.