More Oscilloscope Stuff

Keith Browning · March 19, 2008

We have had several threads on scoping CKP and CMP sensors and I watched and learned... but have very little hands on experience myself. I now have a truck that I am checking signals on but I have to play with the settings to make them recognizable/readable and to look like the many examples I have seen including the pre-loaded ones in IDS.

So my question is, what settings for voltage, time and zoom are you guys using for CKP and CMP? I am selecting the preset auto configure foe each channel and sensor but I have to tweak the settings to make them readable.

Bruce Amacker · March 19, 2008

Hey Guys: I made an error when I took these original captures. I had my 10x button pushed, which made my 80V wave actually 8V. When I went back and re-read this, it didn't seem like 80v was possible, and it's not. Please read the edited version of this post.

So my question is, what settings for voltage, time and zoom are you guys using for CKP and CMP?

With the Pico, not only can you use automatic or normal settings, but it has a ton of automotive presets for common sensors. You can also zoom in on the waves to fill the screen. It is a very powerful state of the art scope with up to a half million captures per screen. It's not expensive, either, with a full blown 4 channel package about 2 Grand with amp clamps and lots of leads.

Idling, I used DC bias, 10ms per division, the CKP went from -2.4v to +5.6v for a peak-to-peak voltage of about 8.0v, and CMP went from -1.5v to +4.2 volts for a peak-to-peak voltage of about 5.7v. The reason they are not centered on the zero voltage base is because of the bias voltage the PCM feeds down the line to verify continuity of the circuit. (If it sends voltage down one line, the PCM expects to see the same return voltage on the other line. If it does not, it sets an OBD2 circuit fault. It's the Comprehensive Component Monitor in action, one of the three continuous monitors.)

Bias:

With the scope on DC bias it shows both the AC and DC voltages, so the waveform "floats" above ground. With the scope on AC bias it shows only the AC portion of the wave so it is centered on the ground plane.

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Cranking:

For some reason I turned the CKP bias to AC where it shows only the AC voltage on the waveform. (Note the wave is centered on zero) Cranking, I used 50ms per division, and the CKP went from -1 to +1v. CMP went from +2.5 to +3.5v. You may notice the bias button on the top left of the screen capture next to the voltage range. This is a 4 channel scope, but I was only using two channels, that's why there are 4 sets of settings.

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