Expert: Roland Finston - 2/7/2012

Question
MHi Roland,

I am BRAND NEW to All Experts and this is my first question!  I am very interested in knowing if full time experts like you are volunteers and do all the fine work all day long for free? If so I must thank you immensely for what you do.

My daughter’s 2005 300C Chrysler has been to the shop TWICE because of codes P0520 and P0522 and they replaced (I think) the Oil Pressure Sensor but now the same thing is happening again. She gets, and she is not clear about this, either a Check Engine or Oil Pressure light with a Oil Pressure chime and the car “Turns Off”. She says this almost always happens while stopped and  when changing gears from drive to reverse or park to drive etc… but says a few days ago it happened while driving down a country road. And she says after the car stops this way she can start it up and go again.

Today I’ve been looking on the internet and I’m confused about the name of the part(s) that can cause these codes (P520 and P522).  People mention the Oil Pressure Sensor, Oil Pressure Sensor/Switch, Oil Pressure Sending Unit Etc. Etc. and I’m wondering if these are separate units – a sensor, switch, and sending unit and so on or if these are ALL names for only one thing, the Oil Pressure Sensor/Switch???

So finally I guess the question is: If they replaced this unit and it keeps happening then what next? Could it be the oil PUMP or an electrical problem? My daughter is under great financial strain and needs my wife and I’s help and I appreciate any guidance you can give us!

Thanks,
Melvin (Curtice)

Answer
Hi Melvin,
You are welcome. I do this voluntarily but there is an option that allows an expert to accept offerings. I choose not to pursue that.
All the various names mean a single specific unit: the oil pressure sensor.
It senses the pressure and electically converts that to a voltage between 0 and 5 volts. The engine computer receives that voltage signal on a wire and then compares it to an acceptable range of voltages. If it is outside that range it sets a code.
Because this happens most often when she is stopped, changing gears, moving slowly it suggests that the circuit is working properly but that the pressure is below that acceptable range for a moment. My experience has been that these sensors are often set conservatively compared to the actual required pressure at low rpm so a false alarm is common. Of course if it occurs when at highway or moderate speed then that would indicate low oil pressure to the degree that you need to stop and determine why to avoid damage to the engine.
Often the least expensive way to solve this is to change the 'weight' of the engine oil at the next scheduled oil change, moving it up one step in number, say from 5w-20 which it may be now to 10W-30, or now 10W-30 to 20W-40, etc. The result of such an increase is that the oil pressure at a given rpm will then be higher that it was before the oil change and thus avoid the false warning most likely.
Of course the level of oil shown on the dipstick should be checked when the engine is cold to be sure low oil level is not the problem.
The stall of the engine, on these occasions may also be the reason for the code, as if the engine is running at low rpm it will have a low pressure. So it could also be caused by something that caused the engine to falter, which would be be found if another unrelated fault code appears.
But I suspect that the engine may be showing its age a bit, which results in lowered oil pressure at any give rpm due to greater facility of the oil to flow through now more open interfaces between the moving parts that it lubricates.
So I would suggest the increase of oil "weight" as the next step when there have been sufficient miles driven on the present oil to warrant an oil change. That would be very inexpensive compared to any more time in the shop.
Roland

Roland