A tale of two codes (P0340, P0344)

[BoKu]

Here's my Camshaft Position Sensor story. A lot of what I've written below is the result of deduction, innuendo, and rumor, so please post up where you see technical errors or omissions.

I had my 2003 Neon for only about a month before a P0340 was my introduction to the Check Engine Light (CEL) and the Chime of Despair (CoD). I was driving along smoothly, and out of nowhere there's that chime and I look down and the CEL was lit. The car was running fine, though (as it continued to do so throughout my saga of P0340 and P0344 codes), was under way and under control and not overheating, so I continued to where I was going before shutting down and doing the key dance to pull the P0340.

As an introduction to trouble codes, it was pretty scary since at the time the car was overdue for a timing belt, and I was worried that "Rationality Error" might be Neon-ese for "timing belt skipping teeth." However, after resetting by disconnecting the battery the CEL went out and the code stayed cleared. For a few weeks, at least. Then a week. Then a day.

From what I can tell from this forum, the most common cause of P0340 and P0344 is a dying or dead camshaft position sensor (CPS). The CPS on the Neon is a black plastic gizmo that detects the poles of a multi-pole ring magnet screwed into the left end of the camshaft. The CPS helps the Power Control Module (PCM) figure out what part of the rotational cycle the engine is in. The PCM mostly relies on the crankshaft position sensor (CKP) to know exactly when to squirt fuel and fire sparks. The CPS just helps the PCM figure out quickly which injectors to squirt with, and which coils to spark. Think of it as looking at a regular twelve-hour clock: It says that it's three o'clock, but without looking out the window to see if the sun is up you can't necessarily tell whether it's three AM or three PM.

Here's the key takeaway from my CPS experience: Beware of N.E.W. Syndrome (Never Ever Worked). Over the course of two months, I bought three camshaft position sensors, of which only the last of the three worked without coding about every 200 miles. The first of the three, a DuraLast 3020 unit from AutoZone, first coded a P0344 within about five miles of installation. After resetting, it coded again within about a minute. A second DuraLast from the same store (and probably from the same batch) would code at least once every hundred miles.

The eventual solution was to buy a Niehoff CPS at Kragen. Three weeks and about 1000 miles after installation, it's still running well and no codes (fingers crossed and knock on wood). If I had known that there was such a range of quality to these things, I probably would have gone straight to the dealership and spent the extra bucks for an OEM unit. The extra twenty bucks would have been money well spent.

The way it seems to work is that the PCM mostly uses the CPS during startup, when you first turn the key. Between the blips from the CKP and the signal from the CPS, the PCM can tell exactly where the crankshaft is in its two-turn cycle after it has turned only about 30 degrees. And that's nice because the faster the PCM figures out where the crankshaft is, the faster it can start sequencing the injectors and the ignition and get the engine started and running.

Once the engine is running, the PCM really doesn't need the CPS at all. It gets good data from the CKP, and all it needs to do to sequence the injectors is count pulses from the CKP and alternate the coils every crank turn. I think I read somewhere that after startup the PCM only reads the CPS every 32 revolutions or so just to double-check itself and the sensor.

My suspicion, yet unproven (but easy enough to prove) is that the engine will actually start and run with the CPS disconnected. I know that the guys who designed these things put a lot of thought into the fallback and limp-home modes, and I believe that they have made the system so that it will work without the CPS signal. I bet that in the absence of the CPS signal, the PCM will try a few revolutions as if it's 3 AM, and if it looks like the engine isn't running (low RPM, starter motor still engaged, high upstream O2), it will flip over and try 3 PM and see if that works.

Another of my personal suspicions, also not proven, is that the real CPS killer is heat. I think that the cheap DuraLast units are probably factory tested at ambient temperature, and work fine, but maybe not so good when they get hot. The Neon installation seems to be pretty hard on them, since they don't get much cooling air where they are buried, and since the hot plumbing for the heater core runs right past the exposed exterior surface of the sensor. There wasn't much of a pattern to when mine coded, but it seemed that more often than not it was late at night and I was using the heater to keep the cabin toasty. Had my problems persisted, I would have fabricated an aluminum heat shield to protect the CPS from radiated heat from the rubber heater core hoses. I still might do that yet.

Here's some info to help track CPS codes: After first coding a P0340 or P0344, the PCM lights the CEL and disables the cruise control. The PCM allows the cruise control again after you shut off and restart the engine, but the CEL stays on. Until the next CPS fault, that is. Everytime the PCM detects a CPS fault, it disables the cruise for the remainder of that driving cycle. So one way to track CPS faults is to keep the cruise control turned on so that "CRUISE" appears next to the odometer windlow. When the cruise indicator goes out on its own, it probably means that the PCM detected another CPS fault.

After coding a CPS fault (P0340, P0344, or similar), If you manage something like two or five driving cycles (start, run, shutoff) without the PCM detecting another CPS fault, the PCM turns off the CEL. However, the code stays in memory, and shows when you do the key dance.

Another poster wrote that the CPS serves as the camshaft thrust bearing, and I saw text to the effect that that is the case with some CPSs in the installation instructions with the DuraLast units. However, I believe that that is generic verbiage that applies to CPSs for some other engines, but does not specifically apply to the Neon unit. My reasoning is that the flimsy plastic CPS is way too insubstantial to make a proper thrust bearing. Furthermore, of the five different CPSs I have installed, removed, and examined, none of them showed any wear marks to suggest actual contact with the camshaft.

One of the things I did try was changing the camshaft target magnet. However, I didn't have a second-gen magnet available, all I had was one that I recovered from a wrecked first-generation Neon. Don't bother trying that, it doesn't work--it codes a P0344 immediately, every time. It seems that they have changed the polarity pattern of the magnet between the 1st gens and the 2nd gens.

Some advice on changing the CPS, garnered from six removals and five installations:

* Try to arrange your day so that the car cools down for at least an hour before you change the CPS, especially if you have been using the heater. It is so much easier to change the CPS when you are not being threatened with second-degree burns.

* Don't even try to change the CPS without removing the battery. That will not save you any time at all. You'll need to disconnect the battery to clear the P0340 or p0344 anyways.

* Getting to the CPS and its retaining bolts is a lot easier if you use a 10mm wrench or socket to remove the bolt that secures the heater plumbing manifold to the left end of the head. Then you can flex the heater core manifold around a bit so as to get to the CPS bolts.

* The perfect tool for removing and installing the CPS retaining bolts is a small 1/4" drive socket wrench, a 3" extension, and an 8mm 1/4" drive socket. The 1/4" drive stuff is nice and small, great for getting past the heater core plumbing, and still carries plenty of torque for loosening and tightening the bolts.

* The most common time-waster when changing the CPS is dropping one of the four retaining bolts while removing or installing them. Everything comes to a halt while you fish around under the airbox and battery tray. One time I had to remove both the battery tray and airbox to recover one of the bolts. By taking a little extra time and effort to prevent dropping a bolt you save literally hours of time searching for a dropped one. Of the three times I dropped a bolt, not once did it ever go all the way through to the ground. It always got caught in the reinforcing ribs of the ATX and I had to go fishing for it.

* As another poster suggested, be very careful when you start threading the retaining bolts into the head. Do not start wrenching on them until you are certain that they are not cross-threaded. I cross-threaded one of my bolts (fortunately only the first few threads), and had to use a 6mm tap to clean up the hole.

I hope that helps somebody else when they encounter the P0340 or P0344 and hear the Chime of Despair.

Thanks, and best regards to all, Bob "BoKu" K.

[ZeroChad]

Great info BoKu!

[occasional demons]

Another of my personal suspicions, also not proven, is that the real CPS killer is heat. . The Neon installation seems to be pretty hard on them, since they don't get much cooling air where they are buried, and since the hot plumbing for the heater core runs right past the exposed exterior surface of the sensor.
Another poster wrote that the CPS serves as the camshaft thrust bearing, and I saw text to the effect that that is the case with some CPSs in the installation instructions with the DuraLast units. However, I believe that that is generic verbiage that applies to CPSs for some other engines, but does not specifically apply to the Neon unit. My reasoning is that the flimsy plastic CPS is way too insubstantial to make a proper thrust bearing. Furthermore, of the five different CPSs I have installed, removed, and examined, none of them showed any wear marks to suggest actual contact with the camshaft.

One of the things I did try was changing the camshaft target magnet. However, I didn't have a second-gen magnet available, all I had was one that I recovered from a wrecked first-generation Neon. Don't bother trying that, it doesn't work--it codes a P0344 immediately, every time. It seems that they have changed the polarity pattern of the magnet between the 1st gens and the 2nd gens.

For the heat issue, remember this thing is bolted to the head, which is every bit as hot as the coolant flowing through the heater tubes, which flow continuously, BTW. So those aren't the problem.

The real thrust control is the timing belt. But if the belt is removed, the cam gear will move in towards the head a fair amount with out the CPS installed. It does have a thrust bearing surface complete with oiling grooves. It will serve the purpose, if something in the timing belt path is misaligned. (worn waterpump)
IDK about the SOHC magnets being different, that is a new one to me.

[Danteneon]

Just to clarify...

The 1st gen cam SOHC magnet is the same as the Non-NGC 2.0 (2000-2002). Part #5269547 The NGC cars do use a different magnet.

[BoKu]

An update:

About two months ago I started getting the P0340 and P0344 codes again. It was the same as before: It would code every month, then every week, and then every day or so.

So I plugged in another CPS, this time an off-brand unit from O'Reilley's. Having swapped CPSs six times now, it was a five-minute job. We'll see how this one lasts.

[occasional demons]

Seems some hold up well, and others don't. 2003 and up target magnets have twice as many polarity switches than 1995 to 2002 magnets. I think this is the biggest reason the NGC ones seem to die more often.

173 thousand miles and gaining on my CPS, and well, I believe all my sensors. If any were replaced before I purchased the car, they would still have well over 100 K on them.



NGC target magnet

[BoKu]

...2003 and up target magnets have twice as many polarity switches than 1995 to 2002 magnets. I think this is the biggest reason the NGC ones seem to die more often...

NGC target magnet

Thanks! That picture suggests how the PCM can synch the crank position within the first 30 degrees of rotation. I'll bet that the big N and S areas are where there are lots of CKP pulses, and the smaller N and S areas are where there are fewer CKP pulses.

Does anyone have a photo of the CKP notches on the crankshaft?

Thanks, Bob K.