I'm having a particularly difficult to resolve issue. A customer brought me a 2008 Frontier with the VQ40DE motor and 6MT. When it came in, the vehicle would not start unless the crank sensor was disconnected. It had a number of codes including a P0335. We were told the vehicle started stalling while driving one day. He personally replaced the crank sensor and both camshaft sensors. What is not clear is whether the hard start began after this or before, but after changing sensors, the problem did not go away. The customer then replaced the crank sensor a second time to no avail. Sensing he was out of his range, he took it to a mechanic. (Not sure the credentials of said mechanic)

The mechanic determined the PCM needed replaced, and after sourcing a used PCM off EBAY, it was installed and then sent to the dealer for the NATS IMU reprogram to allow the vehicle to start. While at the dealer, they advised the customer the connector at the crank sensor was "frayed" and the engine wire harness would need replaced. At this point DTCs U1000 and U1001 appeared.

The customer declined work from the dealer and instead elected to replace the crank sensor connector himself using an aftermarket Intermotor brand connector. When this also did not resolve his issue, he brought the truck to a shop that specializes in aftermarket accessories to rewire the connector on the assumption the pinout was wrong or wiring was poorly crimped. The other shop again replaced the connector, but the issue remained.

At this point, we got the truck and began the diagnosis process. We checked the pinout and found the crank sensor connector had been wired with the power and ground wires reversed to the sensor. We could then get the truck to crank and start with the sensor connected, but still an extended crank with a P0335. We swapped back to the original ECU which removed the U1000 and U1001 codes, but still the P0335/ extended crank remained. We noted there was a timing chain rattle on startup and after checking and ultimately replacing the stretched chain, the issue remained. We verified the flywheel was indexed to the crank properly after noticing the clutch had been changed. We checked voltage drop of the wiring to the sensor and the ECU. We even bypassed the wiring in the harness and still a P0335/extended crank. We replaced the crank sensor a third time and still have the issue.

All things considered, we ordered a used replacement ECU on suspicion the crank signal input might have been fried due to shorted crank sensor wiring. Even that has not resolved the issue.

Am I missing something? Can a cam sensor cause this? Taking the truck to a local dealer we trust to see what is up tomorrow. Will advise what I learn from them.

If only the power and ground were reversed then it's unlikely it blew the ECM. The only thing that could blow is the ECM VB supply, and that would disable a bunch of things besides the CKP. So unless the sensor blew through to the data wire, it's unlikely the ECM was hurt. You can check the sensor by ohming from the ground pin (where the power was hooked up) to the data pin. It should show a large resistance, if not then the circuitry could have blown out and hurt the ECM.

My initial thought is that this sounds like a case of crap aftermarket sensors. The car starting when the CKP was disconnected is a dead-ringer clue to a dead CKP. So were the replacements OE or China cheap?

VStar650CL thanks for the reply. I'm definitely going to check the sensors as you outlined above. I can say all the sensors have been aftermarket, but I have substituted a CKP sensor from a VQ40DE of the same year that literally was pulled from a running vehicle and still had the same issue on this truck but when returned to the running vehicle, it worked fine. I did not back check the sensors we have on the running truck, but I could.

I likewise agree with preference of factory sensors. I suspect we are going to find the dealer will want to swap to factory ones before moving ahead. I just find it unlikely as we have already put in one confirmed as OE before, confirmed as functional and still have an issue.

I have another thought as well. Is there a specification of air gap from the tip of the sensor to the reluctor teeth on the flywheel? This truck does have an aftermarket Valeo dual mass flywheel. Is it possible the gap is too much or such that it affects the sensor sensitivity and it might be missing "seeing" a tooth?

Yes, a wrong sensor gap (too far or too close) will definitely cause misbehavior. Usually the result is a confused ECM that can't fire at the right time, and the result is what you got: Remove the sensor and the confusion with it, and the engine starts on the good cam sensors. If you have access to a scope, you might want to scope the CKP output and look for anomalies.

I wish I had a functioning scope. My scan tool has the capability to expand out with that function but I haven't bought the appropriate accessory pack yet. My old one would but it is trashed. I had a graphing multi-meter but the response rate is too slow. Bottom line: time to get that accessory pack!

And I admit at this point without that signal pattern, it's all shooting blind.

So, a bit of an update:

Took the Frontier to Planet Nissan here in Las Vegas. Complete waste of time. Won't test anything without replacing the complete engine harness, clutch, flywheel, crank sensor, ECU first. So, I paid the diagnostic and they tried to bring it out for us then said the "trans is slipping and there is something wrong." We went back, and found they didn't know how to put it in reverse to back out and instead were engaging 6th gear. (Push down and all the way right and down, dummy)

We ordered a factory crank sensor and the 4 channel lab scope accessory for our scan tool. Money well spent. With the factory sensor the truck starts easily. Idle crank pattern was beautiful! 3 sets of 10 teeth. However, when the RPMs are brought up, there seems to be one set of 10 teeth that drop out above 2000 rpm. When I say drop out, I mean there are between 3 and 4 teeth nice and clean then the signal flat-lines at 12v until the next pattern of 10 show up, and those next 2 are always clean and clear.

When the problem i described happens, the truck jerks and refuses to accelerate. The tach signal becomes erratic as well. In talking with the customer, this is how his issue began back in August, so I believe he "fixed it until it was broke worse."

So I pulled the inspection cover to the flywheel and looked a lot more closely to the the reluctor teeth. There is a little bit of a wave to the reluctor at a certain point. Thre are a couple of teeth that aren't as "sharp" and one with a little nick at the tip. I took a very fine file and squared the one with the nick. Now it appears that one set of 10 when they show on the scope, there is a large square pattern followed by 9 other normal sized square patterns.

So, I'm fairly sure the flywheel is the issue and was in the beginning as well. But as it was allegedly changed in 2014 and there was no other issue until this surfaced in August, I find my self wondering how I approach this. I'm almost ready to cough up the money and do the flywheel then ask questions or even eat it later if the issue gets resolved.

Feel free to voice your opinion. I'm all ears. But one thins is sure: I'm glad we bought the lab scope. I would not even be this close or have this much evidence without it.

Yep, sometimes there's no substitute for eyes-on in the problem area. If the signal is clean everyplace else on the wheel, then I think it's safe to say the wheel itself has to be the cause. It won't be gap, that would be affecting all the groupings unless the whole wheel was dislocated. Check inside the bell, a nicked-up wheel is often evidence of a bolt that fell out or some other debris getting loose inside, like a busted starter tooth.

VStar650CL: no evidence of debris getting kicked around, but I feel like it might have gotten dropped or handled rough enough to warp the tone wheel. It is a Valeo brand part, but im not sure if it's OE or an aftermarket replacement. Clutch was supposedly swapped in 2014 and there was supposedly no issues until August 2021. Doesn't add up.

I dunno, if there's anything loose in there it might be lodged someplace now where you can't see it, like between clutch springs or stuck in throw-out grease. You probably won't know for sure until you split the bell from the engine. Could even be one of the bolts is loose and it's distorting the wheel under centrifugal load.