Hi Guys,

I'm sure this is a very simple question. The check engine
light on my 1998 Mazda Millenia S is on, and the code number
reads P0105.

I learned this to be the manifold absolute pressure (MAP)
sensor. First of all, is this a crucial error code, and if it so
how can I replace it on my own?

PS. I took it to a mechanic and he said MAP sensor is the
same as Boost sensor. He replaced it but the error code
did not disappear. So I asked him to put the old piece back.
If the MAP sensor is the same thing as the MAP sensor as
the mechanic suggested, I wonder why the CEL did not
disappear after he changed it. Any ideas?

Any suggestions is greatly appreciated.

 

well, he is partially correct. the map sensor lives on a bracket right behind the passenger upper strut mount. it does say boost sensor right on it. however, right next to it is a solenoid, and this has been somewhat of a problem, iirc, the solenoid is a lot less expensive than the map sensor. the code is actually map sensor circuit malfunction, so the solenoid is part of this. it could even be the vacuum line going to it has failed. now, as to why the ce lite is still on, perhaps your "mechanic" has no way to reset it. if not, i would not go back there. if you do find out it was the solenoid, i would not go back there. most shops have never even seen a millenia. you are basically paying them to learn. you can reset the lite by disconnecting the battery cables, and touch them together. the car may run strange a bit at first, because this also resets all your fuel trims. but it will smooth out as it relearns the trims.

 

Actually your comments are right to the point.
The mechanic was mostly cursing at the design
of the engine (which I absolutely love). He didn't
have to seem any experience with Millenia, let
alone a supercharger engine.

Now I have the old sensor back (didn't want to
pay $300 which apparently did not fix the problem).
I see that the problem can be at any part of the
circuit, not just the sensor. Maybe there is no
problem with the sensor at all, and it is either the
selenoid or the vacuum as you suggest.

The question is how can I diagnose where the
problem is, and would that be too hard to fix
by myself?

 

He was cursing and you were not because you were not working on it. I like the engine to but it can be trying at times as most things are throughly buried. Were you watching this work being performed that you know where the boost/MAP sensor is located?

 

Yes, I was watching him throughout. Actually I was
surprised that the MAP/Boost sensor is located at
such an accessible place.

I'm still not sure whether I should attempt to
change it myself. It seems quite easy to do since
it is very easy to reach. But as keninn suggested
the error code is MAP circuitry malfunction and
maybe has nothing to do with the sensor. Also
the car is driving without any problems.

Any suggestions?

 

Hi,

Now I got my voltmeter and planning to
diagnose the problem. Could anyone
tell me what shoud be the right voltage
on the MAP/Boost sensor when the
ignition is ON position and when the
engine is running.

In this website I found that the ignition
ON voltage should be between 4.5 - 5.0.
http://www.valvoline.com/carcare/art...1mp&print=true
I wonder if this information is valid
for all cars including Millenia.

Thanks for any help.

 

It is one of the few things that is that accessible oguzakyuz. I am very glad to hear that you know where it is located. Makes things so much more efficient. Kennin is extremely knowledgeable about the Milly as he owns 2 99,s, does most of his own work and is very capable of maintaining his cars.
Connected to the underside of the boost sensor is a vacuum hose. Follow this vacuum hose a very short distance and it will connect to what is called a solenoid valve. There will be another vacuum hose conntected to this solenoid valve. This vacuum hose connects to the intake manifold. With engine idling you will want to remove the second vaccum line to the intake manifoldright at the solenoid valve. Use a gentle twisting motion to remove the vaccum line. The nipple that it is attached to is only plastic and can be broken off if you get to aggressive with it. You should have a good strong vacuum source at this removed vaccum line. I call a good strong vacuum one that will make the vacuum line stick to the tip of a wetted finger instantly. If no vaccum felt then follow the line back to the engine and make sure it is connected. If it is connected then pull the line from the intake manifold and see if you can again feel vaccum from the exposted nipple. This one is metal and not as fragile. If still no vaccum felt then try to force a small piece of wire or drill bit into the nipple to clean it out untill you feel vaccum all the way to the solenoid valve.
Now if you did feel vaccum when the line was first taken off at the solenoid valve then reinstall the line and remove the line at the boost sensor. You should NOT feel any vaccum at the removed hose. If all is ok so far disconnect the electrical connector from the solenoid valve, obtain a couple of jumper wires and apply power and ground to the two pins on the solenoid valve. Does not matter which one gets power and which one gets ground. Once you have applied power and ground to the solenoid valve you should now have vaccuum up to the removed vaccum hose at the boost sensor. If you do not then recheck you electrical connection. Solenoid should make a click sound when power and ground is applied to it. It still no vaccum to the boost sensor you have a bad solenoid valve and not boost sensor.
I never did hear you mention if the trouble code was cleared by the mechanic after repairs were made. CEL should have been off and then maybe later come back on it a day or so. If CEL was never cleared by removing the negative battery cable for 5-10 minutes then it would take a long time of driving for the light to reset itself. It will not just happen instantly as soon as a bad part is replaced.

 

I had the same problem with a PO105 code on my 96S. I replaced the Map sensor thinking that would fix it but it didn't. I then ckecked the vacuum line going to the Map sensor and discovered there was no vacuum. I followed the vacuum line to the solenoidnext toit and there was no vacuum there either. I then followed that line to a plastic tee that had 3 vacuum lines connected to it. I took one look at the tee and realized that was my problem. I returned the Map sensor and bought a tee and finally no more check engine lightNothing like a cheap fix.

 

You snuck another post in there while I was typing apparantly. Excellent that you have a voltmeter.
You should have 5.0 volt reference to one of the wires with key on or engine running. Another wire should have good continuity to ground or 0.0 volts.
The signal wire to the PCM should be 2.37-2.88 volts at idle or with vaccum line to sensor disconnected. This should be just normal atmospheric pressure reading of approx 29.9 on the barometer.
With full manifold vaccum of 25.6 inHG applied to the sensor, the voltage reading should drop to between 0.9-1.1 volts.
It is this change in voltage that the computer is looking to see when it turns on the boost sensor solenoid valve and allows intake manifold vacuum to be applied to the boost sensor.

 

Hi,

Thank you very much for the very helpful instructions.
I'll get my hands on it as soon as the sun goes up again,
and will let you know of the results.

One very quick question though. To apply power and
ground to the solenoid valve, should I use the car
battery as the power source? Sorry for this simple question
but is applying power and ground the same as applying
plus and minus from a battery? (I believe power is plus
but probably minus and the ground are not the same thing
right?)

Thanks a lot again.