MAP sensor? or how does the ECM read manifold vacuum?

[txzaphod]

I have an '02 SR5, RWD automatic, 210K miles, stock except for the deck plate mod to the air box.

I've put one of the ELM bluetooth OBD readers in the diagnostic port to get real time data on road trips using my android phone.

An anomaly I see is that the Manifold vacuum seems to be off. While driving on the freeway, the reading show's positive pressure, as in boost.

How does the ECU read manifold vacuum? I don't see a MAP sensor as a replacement part or on the parts diagrams.

Thank you in advance for sharing your experience.

 

[19963.4lsr5]

You should be looking at the MAF. There is no MAP on the 3.4 any number in your scanner tool is probably an anomaly or that map address has a valid memory location (but is for something else) so it's doing the math for the hex number in the register.


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[txzaphod]

Thank You.

There is no PID 11 (0xB) supplied for MAP, but there is a Boost value provided that is characterized as vacuum when negative.

Either it's calculated from throttle position combined with MAF, or there's a transducer somewhere.

To reference an old joke: "I know there must be a pony under all this horse manure"

 

[AntonioCm1983]

Very good question as well as great response noticed this on several different scan tools i just chalked it up to scan tools miss reading 3.4 liters don't have anything other then a Maf sensor very good question...

 

[19963.4lsr5]

I think it’s calculated.


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