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Mazda CX-7 P0012 Code

niceguyjohnniceguyjohn Posts: 3
edited December 2014 in Mazda
I have a question. I have a 2009 CX7 with 95,000 KLMs. It runs great and I am quite happy with it. However, I am getting an intermittent CEL with a code of P0012. I know that is the variable valve timing actuator. The CEL comes on once a week or so for a day and then resets itself. I have checked the coil resistance as per the shop manual and it is perfect I have also removed the valve and gave it a good clean. It seems to be working perfectly. I know intermittent issues are a pain to diagnose. So here is my question. I assume the signal to actuate the valve comes from the PCL. but WHAT condition or sensor tells the PCL to activate it? I am thinking the real problem is a false signal coming upstream of the valve itself. Or it could be coming downstream of it. Any advice would be very much appreciated.
Thanks in advance.

Comments

  • thecardoc3thecardoc3 Posts: 5,117
    Normal diagnostic routines, and especially testing the actuator solenoid resistance only works with hard failures. Essentially the problem has to be there all of the time that testing is taking place for that to show you that something is definitely bad. Testing like that however doesn't reliably show that something is good.

    The trouble code means that the camshaft timing is over retarded. The PCM looks at the camshaft sensor signal and measures it against the crankshaft sensor signal to determine exactly how the cam and crank are synchronized. Again the code means that the camshaft signal (and therefore the cam) is behind the crankshaft and cannot be advanced, so the PCM shuts the system down. The problem is that once the cam has fallen retarded, as long as the engine is running it takes the PCM supplying oil pressure to the actuator via the actuator solenoid to advance it back into time. (NOTE: When the engine is shut off, springs in the actuator push it back into the advanced position where it locks back into place for the next start-up)

    Diagnostics have several important first checks. When does the code set, immediately every start-up? It could be a timing chain that is stretched, or has jumped. It could be that the actuator (phaser) is unable to return to and lock into the advanced position when the car is shut off.
    (NOTE: This is a two trip monitor so it only sets a pending code the first time that it acts up. It turns the light on with the second failure.)

    Does it act up after it has been driven and the cam timing changed? This could be a failure in the actuator solenoid. The mechanical valve of the solenoid assembly could be sticking from debris. That's why the resistance check you mentioned could be fine and why it really isn't a valid step in the diagnostics. If there was an electrical issue with the actuator solenoid or its circuit you would see codes P2088 or P2089.

    If it only acts up after driving other potential causes are wear in the camshaft bearings allowing a cross feed of the oil flow and loss of the camshaft actuator. It could also be due to loss of oil pressure due to wear or sludging.

    Top techs use advanced testing techniques to troubleshoot systems like this. The usage of digital storage oscilloscopes and pressure transducers for compression testing allow them to directly measure the camshaft timing, and overlay that with the camshaft and crankshaft sensor signals to prove exactly what has failed prior to having to disassemble the engine.
  • Wow thanks for all the details. You are right it only acts up after many driving cycles and therefore the problem does not occur EVERY driving cycle. I know it takes two consecutive driving cycle faults to trigger the CEL. Since the CEL only comes on once a week or less and has maybe 30 driving cycles on it it sounds like a sticky valve (based on your description. Once in a blue moon when the problem occurs i get a terrible bucking and tremendous lack of power, it usually happens on the freeway at normal crusing speed. the rest of the time and by far the majority of the times the CEL comes on and I notice NO difference in engine operation.

    I live in Panama central america at present and the mechanics here are not the best. The one i use (who has the best reputation ) is lost as to what to do next. As I mentioned the valve was already cleaned and re installed.
    Do you think an oil flush would help?

    Any further suggestions??
  • thecardoc3thecardoc3 Posts: 5,117
    edited December 2014
    If the engine is showing signs of sludge, and the actuator solenoid had to be cleaned, then you are probably facing having to replace the camshaft actuator, the timing chain and guides and the cam bearing journals need to be inspected for wear. While an engine flush is usually NOT recommended it might help remove some debris from the engine and especially the oil passages but it will not remove any debris from the actuator. The trick is when sludge starts to develop, it occurs everywhere inside the engine that oil would be present. Any debris forming inside the camshaft actuator cannot get back out and can cause it to start sticking so the only real answer is replacement.
  • Thanks Doc
  • thecardoc3thecardoc3 Posts: 5,117
    I can give you some recommendations in Panama. They are members of the iATN and if they would have trouble figuring this out for you they can go to the group and we can help them.

    Angel Fuel Injection
    Claudio Angell - Technician/Owner

    Auto Cool Plus
    Peter Echeverria - Owner/Engineer

    Inyectecnica
    Luis Alvarez - Owner
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