One of my shops calls me and says that they have a 2000 Nissan Maxima and its a crank no start. I arrive the next day and I see a very clean Maxima with 75,627 miles on it. I reach in and it cranks strong with a good cadence. But, it doesn't even hint of starting. Time to get some information. I quiz the shop owner who tells me the vehicle belongs to a gentleman that spends extended time out of the country at times. He left six months ago and the vehicle was running. Ok, now we have some information. Right away I am thinking rodent damage. Mice and the like love to crawl up into vehicles and chew on wiring. I perform a thorough visual inspection and no obvious signs of rodent damage.
I hook up my scan tool and check for codes and I have a P0335 code for Crankshaft Position Sensor. I also have no cranking rpm on my scan tool when I am physically cranking the engine over. Now at this point some background on this system. This Nissan platform is very common in my area and I have a lot of experience with these vehicles. This year Maxima has a CKP (POS) that reads off the flywheel and is mounted in the oil pan adapter. A CKP (REF) that reads off the front crankshaft dampener. A CMP (Phase) that reads off the Bank 2 Camshaft gear. This setup described is for a 3.0 Liter VQ30DE engine. Now there are some variables. There are two different crankshaft dampener setups. This will alter the CKP (REF) signals. I forget the years off the top of my head that are different. I have many known good patterns from many years on this platform. I just compare to a know good in my library of waveforms.
Typically, if any these sensors are not reading or reading correctly you will get a crank no start. There have also been issues with grounds, revised starter motors, starter motor RFI while cranking, Usually when there is a ground or starter or RFI issue the vehicle will crank erratically almost like a vehicle with a wet distributor cap. This vehicle cranks smooth. Furthermore, I have seen timing chain issues cause a P0335 no start. Time to hook up the scope.
So, here is the a shot of this vehicle cranking with the Pico scope hooked up. This is just a saved screenshot. With the Pico I can save a file with a tremendous amounts of data. Furthermore, I can manipulate the file how I wish afterwards. So what I see here is the correct CKP (REF) pattern for this year and it looks like the CKP (REF) and CMP (Phase) are in proper alignment. What I see wrong is an almost non existent CKP (POS) signal. The CKP (POS) is a hall effect square wave signal where the REF and Phase are inductive AC voltage signals. With this I test powers and grounds at the CKP (POS) connector. All good there. Has to be a bad POS sensor. But, how did a sensor go bad in six months of sitting? I always recommend an OE sensor but due to time constraints an aftermarket sensor was ordered. I installed the sensor as the shop owner was busy and went to fire it up and still no start and this time I didn't see any activity on the POS sensor signal now. Sorry, don't have the scopeshot. I was to busy cursing and screaming. I took a breath and popped the aftermarket sensor out and waved a knife blade across the tip of the sensor with the key on simulating the flywheel teeth and saw nothing on my scope. I reinstalled the original sensor and repeated the knife blade test and had activity. I had a theory now.
The sensor mounts to the aluminum oil pan adapter. I made sure there was no obstructions first. This time around I noticed quite a bit of oxidation in the POS sensor mounting area. I grabbed some sandpaper and scrubbed the area thoroughly. Hit the the area with a little brake clean and popped the original sensor back in. I hit the key.
The vehicle roared to life and ran well. Now, I had POS signal. Let's zoom in a bit.
Let's zoom in even more. The Pico has excellent zoom and resolution qualities.
Now, you can see the POS signal clearly. I tried the vehicle several times it always started very crisply and the waveform was excellent throughout the temperature ranges. I cleared the code,
Here is the actual piece of sandpaper I used with the oxidation on it. The fastener in the picture is one of the screws that hold the cover on underneath the vehicle. The theory here is that the vehicle sat and the oxidation occurred forcing the sensors air gap to increase. I have seen this before on Nissan vehicles with ABS wheel speed sensors. The aftermarket sensor was bad right out of the box. Having worked with these type of sensors in a lab setup I have seen the slightest change in air gap mean the difference between a signal and no signal. Reminds me of a Maxima I checked out a couple of years ago for a shop that was a crank no start after an engine replacement. Long story short the shop never swapped the manual transmission oil pan adapter that came with the used engine (where the CKP (POS) mounts) to the vehicles automatic transmission one. The result no CKP (POS) signal because the sensor was too far away. That shop never made that mistake again.
