# Cam Position Sensor failure - diagnostic



## David3000 (Feb 1, 2012)

I am writing this post because I had trouble finding info about a Cam Position Sensor failure based on the symptoms I was experiencing. Hope this helps someone.

Searches I remember entering:
Pathfinder idles okay but runs rough when warm
Pathfinder stalls when warm
Pathfinder will not start when warm

Symptoms:
Day one - runs a bit rough on the way to a store. Takes over 30 seconds of cranking to start on the way home.

Day two - starts fine. Runs very rough when warm, losing power until top speed is about 35 mph.

Day three - starts fine. I drive to the nearest shop about 3/4 mile away. The truck limps into their lot. I ask them to check the diagnostics. The truck sits on their lot for hours and cools. When they finally check it, it starts fine, runs fine and has no trouble codes. That will be $100 please. Oh, and you could use a tune up. We will do it for $300 but no idea if this will solve the problem you are experiencing...

Note to self: People say most shops will pull trouble codes for free, but shops hate to do anything for free. So if you don't specify this exactly they will charge for a complete diagnostic check (and are justified in doing so).

I haven't been doing my own mechanical work for a number of years, but money is tight so I figured I'd give it a go. I paid the $100, limped (max speed now about 20 mph) to a parts store and bought a cap, rotor, wires, plugs, air and fuel filter. No start - so walk home... Couple hours later got a ride back. On the way home the truck loses more and more power then dies about 100 yards from my house. Walk home, have dinner, go back and drive into the garage.

Now I have a CES light! Apparently, it requires an extremely severe / long lasting failure to set the switch in the ECM/PCM. There is no way I'm driving this thing back to the shop, so I order the Equus 3030 OBD2 scanner online.

I do the tune up, but it doesn't help. Still, that eliminates a lot of possible causes of the problem and it's never a bad thing to do.

The scanner comes and I pull a P0340 trouble code - Camshaft Position Sensor Circuit Malfunction. Looking back, the symptoms I experienced are in line with this problem: starts idles and runs fine cold, runs rough and eventually stalls when warm, and won't start when warm.

Incidentally, a MAF sensor failure exhibits many of the same symptoms, but I think they occur even when the engine is cold. I cleaned the sensor just in case (with MAF cleaning spray). It made no difference.

Some vehicles have a small CPS on the engine, but the '99 Pathy has it embedded in the distributor. Chilton's has a complicated way to test it, but it is more than I was willing to do. I took a chance and ordered a remanufactured Hitachi distributor. Installation took about twenty minutes. I took a photo of the _exact_ position of the original rotor, then made sure the new rotor was in the identical position. Re-attached all wiring, crossed fingers and turned the key. It starts right up. Yea!

I let it warm up then drive it up and down the driveway, then around the block. It seems fine. Get out a timing light and unplug the TPS (as I learned in this thread http://www.nissanforums.com/pathfinder/169410-1999-pathfinder-timing.html#post1348692 ). It was about 11 degrees so I adjusted it to 15 degrees. I reset the trouble codes with the scanner and drove around for a while. No new codes appeared. Most of the monitors cleared after about ten minutes on the expressway, except for the EVAP monitor. Still trying to figure out the drive cycle for that one...

Finally, since the Pathfinder had been running so poorly, I dumped a bottle of fuel injector / valve cleaner in the tank. Happy Pathy again!


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## dhadder1 (Jan 22, 2012)

When my cam position sensor went bad on my 05 pathy the only symptoms were that it would turn over for about 15 seconds before it would crank and sometimes it would die at a stop sign. But no loss of power or any of the above.


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## David3000 (Feb 1, 2012)

Thanks for your reply dhadder1. This was a difficult problem to diagnose because not everyone has all of the same symptoms. Your truck would "turn over for about 15 seconds" before starting - that was on my list. You mentioned yours would die at a stop sign. Do you remember if this only occured when the engine was warm? One of the keys for me was that it did not stall when cold. Also, did you get a CES light and trouble code?


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## dhadder1 (Jan 22, 2012)

The delayed starting was hot or cold. I did get a light and trouble code. I don't remember the number but it was definately the cam position sensor code. And no other performance issues like loss of power. Also on my 05 the sensor was on the back side of the passenger side head.


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## David3000 (Feb 1, 2012)

I did find pictures of head mounted sensors, but ignored them since mine was in the distributor. That probably cuts the replacement part price in half.

The difference may be that the design in the '05 is less likely to cause catastrophic failure or perhaps it depends on *how* the CPS fails. Thanks for sharing.


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