This is basically a case study to add information regarding the "inverted waveform" phenomenon that we can encounter.

So the shop owner got a 2005 Nissan Titan, 5.6 L (VQ56DE ?) at auction. It was setting DTC P0355 "CKP sensor ckt". He had our helper r&r the CKP sensor. No fix. So, I get to look at it.

Like all good boys, with a DTC for a CKP (or CMP) sensor, I scoped both at the ECM. Blue is CKP, red is CMP. I got this;

[2005 Nissan Titan LE, ECM/Inputs/Outputs Waveform]

Comparing that to a known-good from the library, and the Nissan SI image in All-Data, the CMP is upside down. I know that has been discussed before. There are varying opinions on the subject. Some say that ECM's don't "see" waveforms like we do. Our eyes see lines with humps. Riding low and jumping high, or vice versa. An ECM sees "transitions", or "only sees a falling edge" or "rising edge" etc. Well since no one agrees...and the falling/rising edge theory shows this engine as being out-of-time...and the engine ran just fine...I replaced the CMP sensor.

Now the signal looks EXACTLY like it is supposed to;

[2005 Nissan Titan LE, ECM/Inputs/Outputs Waveform]

and the DTC for CKP does not set. Amazing!

Additional info;

1. I was using a G-Scan. For those not familiar with that great scan tool, the DTC screen is live, and you can clear a DTC from that screen. (no backing-up to a different menu). If I cleared the DTC KOEO, the DTC set as soon as I cranked the engine. If I cleared it while the engine was running, it came back instantly. 2. Curious if my theory that a "wrong" CMP signal could set a CKP DTC, I unplugged the CMP, however this resulted in a P0340 "CMP sensor ckt" and a crank-no-start condition. 3. In the DTC criteria for P0335 it mentions the CKP "...signal is not in the normal pattern..." but does not say anything about "relative to (something else)"... and of course the CKP was NOT irregular here, the CMP pattern was. 4. After all my reading on the subject, I was almost sure it was a bad ECM or stretched chain. (nope....LOL) hope this helps someone else someday.

aloha from Maui.

and a very special thanks to the donor of my PicoScope

Geoff from Hawaii

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