Hello, Newb here, had our 2nd Scion xB for a few months..
 

My fiancee has been telling me she's getting terrible fuel mileage, but I kinda expected a little of that because we sold an 04 with a 1.5 and got this 08 with a 2.4. It's a real powerhouse compared the 04, so one would assume, (and reports are), that the fuel mileage is going to be a bit lower. But I had occasion to hook my scanner up recently, to look at the reason for a maintenance light, (turns out it's time for an oil change), but while in there, I decided to look over some data stream, and found an intake air temp reading of -38°F.... Good explanation for the poor fuel mileage. So I ordered a MAF, (air temp sensor in built into the MAF), installed it a couple days ago, then scanned again, NO CHANGE. Today, I traced the wiring from the air temp sensor to the ECM and it has continuity.

Alldata says:
- If there is an open circuit, the tester indicates -40°C (-40°F).
- If there is a short circuit, the tester indicates 140°C (284°F) or higher..

So, new sensor, exact same indicated reading on scanner, both sensor wires intact, anyone have any ideas?

Thanks in advance for any help!

_______

Is your fiancee a 'spirited' driver? I have a tC with a 2.4 that averages 27mpg hwy/city. Spirited driving lowers my fuel consumption as much as 10 mpg.

She doesn't drive this one any harder than the 04, in fact she shifts a little sooner because it has so much more torque. I'm not as concerned with the fuel mileage aspect as I am with it running as if it's -38° outside. At this point, with some additional diagnostic info from Alldata, I am suspecting I will need to replace the computer....:frown:

Do you happen to have a friend that would allow you to borrow theirs and see if it also shows the odd reading?

I wish, that would be really cool...:money:

A bad computer should throw a CEL.

Are you talking Scion specific? Because as a general rule, bad ECMs don't always throw codes, in fact, about 30% of the time, they don't...

Do the wires still have continuity if you jiggle them around a bit?
Any corrosion in the connectors at either end?
If you measure the MAF sensor resistances thru the connector wires are they the same for both new and old parts?
I don't know how this MAF works - is it a heated wire that is cooled by the air stream? Is the heater system working?

Just trying to think of things that may be cheaper than a new ignition box

Yes, No, didn't try, (there is no spec for that), and yes, pretty much all MAF are heated wire these days, with the ECM monitoring how much voltage it takes to maintain the specified temperature.

Hmmm... Wonder if you can fake out the reading with a resistor placed in series (to raise resistance) or parallel (to drop resistance).
Might be able to buy a cheap Potentiometer to find out a resistance value that works ??

Sometimes you just have to brute force things (like I had to trying to get an alternator to put out the right voltage)
Sometimes you just have to turn off the autopilot!!!

That's a thought, for sure, 8)