TOPIC: Data Displayed for sensors not installed?

I have a question that's puzzling me. When using a scantool showing real-time data streams on my 02 Subaru Outback, I've seen data displayed for sensors that aren't there.

This car is emissions certified for both California and Federal emissions standards. No surprise-we see a lot of Calif smog equipped cars here. The air intake ducting has NO MAF or IAT sensors on/in it. I've found 2 holes that look like likely install points for an IAT in the plastic ductwork. But there's no loose/extra wires or plug connectors, and no MAF sensor. I think it's convienient that the ductwork is so simple and free of clutter!

And yet, when I hook up my scantool and select entire data stream to view,-- as it's running there are values displayed for both MAF and IAT. I can only guess that those values are extrapolated, synthetically shown by the ECU.

So, I'm wondering if anyone here can comment on this situation...?

Tracy G

If those readings are interpolated from other data, they have to be pretty confident in their engineering...or OBD2 is a scam.
what sensors ARE on the vehicle other than o2 related to engine/powertrain?

Greg, here's what I know so far. TPS, MAP, ECT, Some kind of RPM sensor. (Obviously there's one!) A power steering sensor. Voltage regulator, again obvious. Mainly it's a mystery to me, how there could be values shown on my scantool, for IAT and MAF. Since they aren't there. I looked at several later model Subaru's at the boneyard. Many/most did have a MAP, I didnt look for IAT's. The ones closest to my Outback- had the engine already yanked ant the underhood area trashed. So I've not yet seen another 02 Outback 2.5L 4 cyl.

so far I ascribe the missing IAT and MAP, along with the 3 cats, also the upstream/downstream O2's being on the same first upstream cat, to it being Calif. smog certified. I base that opinion on the fact that my '85 Subie, is also Calif. smog equipped, and there are differences in it's emissions stuff vs. Federal spec.

Another think I plan to watch, is the next time(s) I use the scantool, I'm going to watch the IAT and MAP values, to see just how much they do fluctuate. Lastly, from what little I know, Subaru is an odd duck Co. They reportedly are/ have been stingy about sharing critical spec's, data, and so forth with the aftermarket. I'm sure there is some stuff peculiar to Subaru's in general, besides the cars' basic designs.


Other than this odd business on the OBD data, these are great cars. Mine runs quite well, and the 06 Forester I grooved recently ran like a young Striped Ass Ape!!

Tracy G
Gadgetman Reno NV

Tracy, our convo here might be why Ron posted that “ECU hacking” document - from what I’ve briefly skimmed in it, I believe there are a whole pile of answers for all of us. I would even go so far to say that it might turn into required reading for us here- especially since most of the cars anybody coming to the groove will be working on are from the last 20 or so years and they basically all have some sort of computers with sensors. The former teacher in me is thinking that an intro to sensors in a car and how they work would be the place to start so we know what the computer looks at and the hows/whys of them before getting into grooving and sensor modification. It’s a bunch of simple and easy mods, but the knowledge I’m talking about will help everyone get the best result more often. That makes us all look better and more professional, and will add credibility to the groove. There’s a reason dealers hire technicians rather than mechanics, and those techs are only going to get more specialized, just like lawyers and doctors and accountants and engineers, as cars evolve and improve.

In your case, the computer can likely infer that at X rpm and y degrees TPS when MAP is Z inHg vacuum, the engine is drawing in Q g/sec of air (MAF reading), verified at exhaust by o2s. That's what I meant about Subie being confident in their engineering- they've tested and put together the data on engine flows.

does your car's dashboard tell you when a turn signal or brake light bulb is out? That's an indicator of a CanBus equipped car, and you should read up on all the data moving on the car's internal network - if you thought OBD was over the top, prepared to have your world rocked...and then extend that to cars with factory-installed 4G (and soon, 5G) infotainment/communications systems, and then autonomous cars...Big Data has come to the automotive world.

My point here is we need to know more than we used to when it comes to working on cars. Gadgetmen moving forward, like dealership automotive technicians, have to have more knowledge than ever before to understand a car's inner workings and be able to diagnose problems and effect repairs/formulate workarounds. Carbs and points were replaced by EFI and CDI; what comes next remains to be seen...maybe plasma ignitions and vapour induction systems, or complete replacement by solar-powered electric vehicles with supercapacitors and regenerative braking systems. And maybe there won't be a steering wheel in any vehicle, and you might not be able to buy/own a car or be licensed to drive.

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