The P0340 Camshaft Position Sensor Circuit Malfunction Thread

[kansei]

yay! welcome to the fun!!

So you have a dreaded P0340 code. Chances are, if you found this thread via the search function on the site you're here because your car is broken down on the side of the road and you are quite sad.

I'll be compiling all the diagnostic procedures, part numbers, etc that might relate to this problem to save people time in the future.

First off, as this is a code any vehicle (not just Mazda) can get, there's a lot of good information on it online:
http://www.obd-codes.com/p0340

The symptoms of this code (listing them here so when people search they may find this thread in the future):
- hard start or no start
- rough idle
- lack of power
- broken down on the side of the road

Though it may seem obvious to just run out and replace the sensor (since it's so easy to install), don't count on it fixing your problem. It does for some, but for others not so much. Here is a list of things to try:

- check the plug and wiring leading to the cam position sensor. This sensor plugs in on the left side of the valve cover, toward the front of the valve cover. It's the only sensor there, can't miss it.
- unplug rear oxygen sensor. Don't ask why, but it has worked for at least one person. There may be a short in the wiring.
- Check for voltage continuity for the cam position sensor. CMP (CaM Position) sensor terminal A and PCM (ECU) terminal 85 CMP sensor terminal B and PCM terminal 86.
- check the wiring to the crank position sensor, and the sensor itself. Check for voltage and continuity on that sensor as well (need to dig up the ecu pins for it)
- replace the cam position sensor

Here is a good primer on diagnosing automotive electrical problems, going over how to check for continuity, voltage, etc:
http://www.aa1car.com/library/tselec.htm

Part Numbers:
Check www.onlinemazdaparts.com or if you race your mazda www.mazdamotorsports.com. Dealerships don't stock either part.
N3A1-18-221A - Camshaft Position Sensor. This part retails for around $140 (as of August 2008).
FSD7-18-221B - Crankshaft Position Sensor. Around $90. Looks like it comes with the short wiring harness piece that leads to the valve cover area.

This thread is a work in progress (currently experiencing this problem myself)

[kansei]

DTC P0340 CMP sensor circuit malfunction
DETECTION
CONDITION
• PCM monitors input voltage from CMP sensor while MAF is above 2.2 g/s {0.29 ib/min}. if PCM does not
receive pulse signal the proper pulse signal timing basis on the CKP sensor signal, determines that CMP
circuit has malfunction.
Diagnostic support note
• This is a continuous monitor (CCM).
• MIL illuminates if PCM detects the above malfunction conditions during first drive cycle. Therefore,
PENDING CODE is not available.
• FREEZE FRAME DATA is available.
• DTC is stored in PCM memory.
ON-BOARD DIAGNOSTIC [ENGINE CONTROL SYSTEM (FS)]
01–02B–81
01–02B
Diagnostic procedure
POSSIBLE
CAUSE
• CMP sensor malfunction
• Connector or terminal malfunction
• CMP sensor is dirty.
• Short to ground between CMP sensor terminal A and PCM terminal 85
• Short to ground between CMP sensor terminal B and PCM terminal 86
• Open circuit between CMP sensor terminal A and PCM terminal 85
• Open circuit between CMP sensor terminal B and PCM terminal 86
• CKP sensor pulse wheel malfunction


Note that the MAF is mentioned, so if you currently have any MAF issues... take that as you will. For example, my car gets a MAF input high code when I drive in the rain, and the P0340 was triggered right after it. Probably coincidental, as the MAF CEL thing has been happening for years and never the P0340. I have heard from a few Protege people the P0340 labeled as a "scapegoat" code, meaning the car may trigger that code if something is up with any of the many systems affected by cam/crank position sensors.

Also note that in the above, CKP is the CranK Position sensor, CMP is the CaM Position sensor