Inverted camshaft sensor
Ill start out by saying this car is already repaired. A new cam sensor from Nissan was the fix. My question lies more in the scope pattern, the sensor, & PCM monitoring. The code was for the VVT system not functioning correctly. Specifically, the intake cam did not phase to the correct degree when commanded. The shop I was assisting changed the oil, and replaced the VVT solenoid in attempts to fix the issue to no avail. I activated the VVT intake solenoid and confirmed it was actually phasing and to the desired amount. I was expecting to find the engine was out of time, or at least a stretched chain. After scoping the cam and crank sensors and comparing to a known good, I found that was not the case, What I did find was that the cam sensor signal was inverted when compared to several known good wave-forms that I was using to check timing alignment. I have read about "cam flop" on certain engines while cranking or during idle causing a strange waveform, but this is something different. This persisted at all RPM ranges. I have also read about an totally inverted cam signal, and the fact that it may not affect the PCM operation at all. I believe this topic has been discussed before, but it's the first time I have personally encountered it. (I actually read something about rotating the sensor 180 degrees in it's bore to change the pattern). I'm wondering not only how the sensor can completely invert the pattern, but what the PCM sees from the cam sensor. Is it just watching switch time, or specifically looking for rising and falling edges to determine the position? Do the rounded edges of the pattern affect the PCM when the pattern is inverted since they occur on the opposite side of the pulse? Since I confirmed the sensor was the fix, I'm just trying to understand exactly how this caused the fault that it did. Hoping someone smarter than me can shed some light on that. I know this is the place where those people could be found. Thanks in advance!
Hi Sean, pretty cool fix. You mentioned the "cam flop" waveforms we're seen in the past and that it looks like the signal inverts. However, if you pay close attention to the falling edges of the signal, they occur at the same time. Now, on to your inverted signal. Here's an excerpt from the SI: The CMP sensor consists of a permanent magnet and Hall IC. When engine is running, the high and
That makes complete sense if the PCM is watching for the placement of falling edges. With that pattern it would believe the engine is completely out of time. I looked through the DTC index for this vehicle, and the P0011 is the only timing related code that it has the ability to set. I suppose a different vehicle might set a cam/crank correlation code in this scenario.
I diagnosed a 2008 Nissan Sentra 2.0L this week that was hard to start and setting a P0340. Someone had already replaced the CMP sensor. This was the CKP/CMP waveform from that vehicle: I found some known good waveforms on iATN. Based on those known goods, my signal didn't appear to be inverted, but the signal was retarded. I diagnosed it as a stretched chain. So, why did yours set a P0011 and
I think you are right on the money. Thanks for the information, It's pretty clear in my mind now. I always feel better when I know exactly WHY the code set and WHAT the PCM was unhappy with.
I've said forever in this industry, if you stand still long enough all of the unusual problems return. Very similar to your problem, When GM was using the HEI Ignition system with a distributor, the pick-up unit produced an AC voltage signal into the module. The 2 wires used were Green and White, On most of the Pontiacs only those two wires were switched, because of that, the waveform started in
It is crazy how you see certain failure patterns repeat themselves in newer vehicles after years of not seeing them
Wow Jim,... I remember that. The distributors rotated in the opposite direction. Does that mean we are the really old guys or are we still OK because we CAN remember that. ;)
It means we are SENIOR information Specialist....LOL BTW - Brandon Steckler speaks very highly of you, I believe I meet with you years ago while doing some research and development work with ASPIRE.
I wrote up one of these a few years back over on iATN. That one had an inverted CMP signal and was setting a CRANK DTC! (P0335). I was mainly concerned that, at the time, many people were insisting that inverted signals were irrelevant. I think any day of any week any PCM can set any DTC for ambiguously defined reasons, and we are damn skilled if we figure those out. :-) Hopefully Scott allows
I had read the same thing, that the inverted signal would not effect the PCM, which made me question what it’s actually looking at. Obviously it does make a differenc. There was a time I’d just throw a part at it and not think twice. Using a scope really makes you think about what’s really going on.
Just be careful not to get stuck in analysis paralysis :-) Best way is to scope a lot of things that work just fine, to help see what "anomalies" are actually irrelevant. I'm guilty of not doing that nearly enough because of the floor plan layout here. (It is a project to get my scope out and set-up, and I can't NOT put it away for safety/security)