Nissan Murano Inverted Cam Sensor Waveforms

2006 Nissan Murano 3.5l

(I forgot my Verus at the shop, but will upload better waveforms when I have the chance...)

Crank no start, single spark event, 3-4 injector pulses, then no control.

After a long crank, sets codes for bank one cam sensor circuit fault, bank two cam sensor circuit fault, crank sensor circuit fault.

All three sensors are 12v, 3 wire hall effect sensors.
Power, ground and signal at all three are good and consistent during cranking.

At this point, I want to see if there is a correlation issue.
As luck would have it, Nissan supplies a sample waveform in the service info!

My waveform appears to be off, but beside not lining up, the cam sensor seems to generate the opposite signal...

Yellow B2 CMP (front bank)
Green B1 CMP (rear bank)
Blue CKP

Note that the sample shows that the signal goes from low to high, where as mine goes high to low...

I just happened to have a perfectly good running 2005 Nissan Murano on the lot, so I parked it behind the no-start Murano and hooked up the leads exactly the same and plugged in the scope without changing any settings.
This wave form matches the sample from Nissan.

So what's the deal No-start-nissan?

Why is the signal apparently inverted on the problem vehicle?

I'll be happy to e-mail the .vsm files to anyone who would like to view them. I am thoroughly confused, and welcome discussion!

I've heard of this before! Something goes wrong in the sensor itself, causing the signal to invert.

The weird part is that some cars get away with it and have no issues. Weird, right? Depending on the YMM, the PCM only looks at where the transitions occur, and doesn't really care if it's high/low/whatever.

I'm on my phone, so it's tough to see, but how's the revelationship on the problem vehicle? If it seems OK, I'd be confident in at least doing cam sensors, if not all three.

The transitions never align on the problem car, I'm pretty sure the timing is off. Plus the guy working on it before me put a bank 2 cam sensor in it after reading codes, all be it a used sensor.
I am tempted to take the sensors from the running car and put them in the dead one to see if the polarity is corrected, but I still don't think it will run.

I have never heard of this phenomenon! I'm seriously glad I had a running vehicle to compare to.

Maybe off in my logic here, but if "off" is "on" and "on" is "off", could the wave form essentially be shifted forward the exact length of each transition?

At first I assumed that regardless of the polarity, the transition would occur at exactly the same time. But if the signal is truly inverted, would the leading edge of the transition just swap with the trailing edge, or could the transition be advanced?

If you retard each inverted cam transition on the problem vehicle by the exact width of the transition, they would fall within the synch window of the crank signal.
I was editing captures to include 720 degrees of rotation to post when I noticed this.
If course the battery died on my computer before I could finish, but I think you can see what I'm referring to in the pics posted before.

These are better captures showing 720 degrees of rotation. Cursors are placed so as to reflect min max voltages.
First is the known good: It looks like the signal "flips" part way through the pattern ch1. Weird... So I guess my late night hypothesis about the possibility of the signal being inverted and therefore possibly "reversed" was incorrect.
Ch1 Yellow B2 CMP
Ch2 Green B1 CMP
Ch3 Blue CKP


Next is the no start with the inverted cam sensor signals:
Ch1 Yellow B2 CMP
Ch2 Green B1 CMP
Ch3 Blue CKP


And finally, the example from Nissan:


My curiosity got the best of me, so I did go in early put the known good sensors in the no start Murano. As I suspected, it was still a no start, but once I had it in my head I had to try it
Unfortunately it was raining this morning, and the cars were outside, so no scope captures of that experiment. :blush:

I'm interested to see how many more instances of this "signal flipping" I'll come across considering there seems to be an uncomfortable number of these Nissan 3.5l powered vehicles coming through the shop. Hoping someone has some input considering what causes this occur.

I read from another forum the way Nissan cam signals behave. This individual had a 2007 Nissan Sentra MR20DE with a no start until he unplugged the sensor and the car ran. His capture showed one cam instead of two and there was cam flop with the sync being good. Raising the rpm to 1500 should have eliminated the flop but it didn't. Cam flop should give you longer pulses during cranking and idling with low oil pressure. In this case replacing the sensor fixed it. So it looks like these signal behavior is common as you saw on the known good capture how the signal flipped on Ch 1.

Thanks for the reply
I've been reading about other similar instances on iATN. No one really seems to have a solid answer as to the "why" it happens.
Some say that it can be attributed to low voltage and low cranking speed. Sometimes it happens with a no start, sometimes it happens with a code and sometimes it has no effect on operation. But who would be looking at the signals for a grin unless there was a code or symptom leading them there?
It does seem that regardless of the "flip" the sync pulses should always align. At least from what I've been able to gather. I am curious if it could have a negative effect on ignition timing.
I think there's another Murano coming in for AC service this week. I want to check that one out too, cranking clear flood and running.

Just found this pearl of wisdom in the comments of the ScannerDanner Premium Lexus no power case study:


I hope the author will be willing to teach me something about this "cam flop".

This is a classic example of cam flop making you think waveform is inverted -- it is not!

See this attached ... I don't think you have a problem with sensors or timing but with wires back to computer or computer itself

I did NOT finesse the alignment study of cmps to ckp so maybe they are off - also without seeing the whole waveform I cannot judge it fully - I am making assumptions - but I hope you see my drift and take it into a more clinical view/assessment

I take take that back - after a re-look I see Bank 2 could be off

edicola12 wrote: I take take that back - after a re-look I see Bank 2 could be off

Thank you for taking the time to respond to this topic.
I'm confident that the timing is off and the cause of the no start. From what I can see the cam events never align with each other or the crank events, especially if the trailing edge is truly the "signal" the PCM waits to see as had been suggested.
The inverted signal kind of made me question my understanding of how these sensors generate signals and how the PCM interprets them.
The more I read about it, the less important it seems to be, but something to be aware of none the less.

Yup timing off Based on my jpg bank 1 is on but bank 2 is about 20 degrees retarded - this probably would cause a hard start or no start even in otherwise undamaged engine but you may have consequential bent valves

Good luck keep us posted

Great stuff edicola12. Thanks, sir!

Noah, I just now noticed the stuff you have written in paint marker on the top of your Verus. :lol: Any more info written elsewhere?

Tyler wrote: Great stuff edicola12. Thanks, sir!

Noah, I just now noticed the stuff you have written in paint marker on the top of your Verus. :lol: Any more info written elsewhere?

Every where!

Noah,
would the engine start with cam sensors unplugged?

No, it would not.