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Waveform question cam sensor

posted Jun 30, 2016 16:56:17 by kewl427
Hello everyone, 2002 Jetta GLS 2.0 AVH Has a code P0343 cam sensor issue. I have a Verus with 16.2. Followed instructions on hook up through lab scope. Is says voltage going to sensor is a 5 volt , and when I checked it it was correct. Ground was good. So when I checked the signal it was off the scale but was a square wave pattern but was 12.8 to 13.0 volts. My question is why did it go to 12.0 volts or is this correct... ?? Bill
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16 replies
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AndyMacFadyen said Jun 30, 2016 21:59:55
What voltage is on the signal wire with the sensor disconnected ?
A Hall Efect sensor can't generate voltage it is in simple terms a transitor on off switch operated by magnetic field.

You can do a sanity test with digital voltmeter with the engine cranking or running the voltage on the signal wire should be flicker up and down but will always be less than the voltage supply to it.


"Rust never sleeps"
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Noah said Jul 01, 2016 00:57:40
Hi kewl427. Thank you for posting year, make, model and engine code!
That's a weird one, I would expect a 0-5v square wave. Like Andy says, it can't make it's own voltage. I'm also curious about about the voltage on the signal wire unplugged.
Also the voltage on the feed wire connected vs disconnected.
The manufacturer has you check the feed wire against the ground wire (disconnected), it says to expect between 4v and 6v.

Here is a link to a free premium channel lecture from section 21 covering hall effect sensor testing.



Massachusetts, USA
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kewl427 said Jul 01, 2016 03:45:40
The signal was 12.38 and 5 volt ref.. was 5.0 volts and the ground was 10mv..All this voltages was with sensor unplugged check at ecm side... I just thought it was weird when in component sensor check , when snappy gives you the preset its normally correct and within the voltage limits unless something is wrong.. I have to move spects from 10v to 20 volts to get pattern on the scale... Also when I went to signiture test it was right on spect... Thanks for your imputs... Bill
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Tyler said Jul 01, 2016 17:48:28
I got curious about your issue, decided to see if I could find a known good over at iATN.

I can post the image later today, but all the waveforms I found do show a 0-12V signal out of the CMP sensor. The only way this makes sense (to me) is a pull down CMP sensor, with 12V supplied by the PCM. Your voltage readings with the sensor unplugged tend to support this.
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Tyler said Jul 01, 2016 17:51:12
Also, thanks from me for posting all your info, too! Made finding a good waveform so much easier.
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Dylan said Jul 01, 2016 18:27:36
I got curious about your issue, decided to see if I could find a known good over at iATN.


Nice Tyler. Have been scratching my head when I read this.

The only way this makes sense (to me) is a pull down CMP sensor, with 12V supplied by the PCM. Your voltage readings with the sensor unplugged tend to support this.


Can't think of any other reason either. Still confusing though..
Belgium, Europe
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AndyMacFadyen said Jul 01, 2016 21:13:16
I have seen it on a crank sensor Vauxhall/Opel Vectra a 12v pull down.
"Rust never sleeps"
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kewl427 said Jul 02, 2016 03:38:50
First of all I want to thank all for the help.. Tyler I also did the same thing prior too posting on this forum , and checked with IATN and saw the same, but still I was not sure. Truth is I did put in a new cam sensor (dealer) and the pattern was exactly the same. UGH..but the check engine light did stay off.. Customer did say it was a intermittent problem..So again thanks to all ... Bill ...
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Tyler said Jul 02, 2016 14:43:47
Ah yeah, gotta love the intermittent ones! Still, well done doing your homework before replacing the sensor.

Nice to see other iATN members posting here, too. That waveform library is a pretty awesome resource at times.
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Dylan said Jul 02, 2016 14:51:08
Still wondering why you measure a 5v reference and not 12v.
Belgium, Europe
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Noah said Jul 02, 2016 16:10:12
Dylan said about an hour ago
Still wondering why you measure a 5v reference and not 12v


Glad I'm not the only one!
Massachusetts, USA
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Inge_Jeppesen said Jul 04, 2016 15:44:19
Ford also use these 5 volt ref and ground sensors that pulls down a 12volt signal from the pcm. Not uncommon at all.
Norway
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Noah said Jul 04, 2016 16:00:37
So you would have a transistor ground, constant 12v feed (until the base is turned on) and 5v square wave on the base circuit.
Massachusetts, USA
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AndyMacFadyen said Jul 04, 2016 17:53:25
I think the key with this type of hall effect sensors might be think of them as a relay with the magnetic field switching on the ground of relay coil and unlike with a TPS or temperature sensor not to think of the 5v as a reference voltage but as simply the power supply for the coil.

"Rust never sleeps"
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Dylan said Jul 04, 2016 18:07:27
You can do a sanity test with digital voltmeter with the engine cranking or running the voltage on the signal wire should be flicker up and down but will always be less than the voltage supply to it.


Still kinda confusing...
Belgium, Europe
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