How to Test a MAF or MAP Sensor With a Multimeter – Plus an Operations Guide

hey how’s it going do-it-yourselfers today we’re going to go over how a mass or mass airflow sensor works but not just that we’ll also cover how a map or manifold absolute pressure sensor works and then we’ll go over how you can test these two sensors using nothing but a basic multimeter alright first up the mass airflow sensor all right so your mass airflow sensor is usually going to be located right after your air filter box and this air hose that goes from your air filter box to your engine as is the case on the Saudi or as is the case on this 2003 Ford f-150 it’s actually located right on your air filter housing now the job of your mass airflow sensor is to measure the mass of air that’s entering your engine and then it provides this information to your car’s ECU your car’s computer uses this information to time your fuel injectors and adjust your air fuel mixture and the way that this is done on this Hotwire mass airflow sensor is through that element in other words the hot wire that’s in that plastic housing which you guys might just be able to make out on these sensors your car’s computer is supplying this hot wire with constant voltage and also constant ground as air flows through this sensor or through the housing it cools down the hot wire as a result the resistance of this hot wire changes resulting in a different voltage drop across this sensor that voltage drop is transferred back to your course computer through the signal wire and that’s how your car’s computer knows exactly what’s the mass of air entering your engine so typically the connector that goes to this mass airflow sensors is going to be either a 3 4 or a 5 pin connector as is the case on the sensor if it’s a 3 pin connector we already know what those three pins are for if it’s a 4 pin connector that’s usually just an extra ground for the casing to get to clean up the signal that’s going back to your cars computer and if it’s a 5 pin connector you usually won’t have a sensor case ground instead you have the two extra wires are going to be for your Inlet air temperature sensor which are housed with your mass airflow sensor into this housing you’re going to have one constant voltage usually 5 volts for that sensor and then the return signal line to your car’s ECU so again on this 5 pin connector right there on the side is element for inlet air temperature sensor all right next up manifold absolute pressure sensors your manifold absolute pressure sensors are usually connected to your intake manifold by a vacuum line as is the case here or there directly bolted into your main take manifold now the job of your manifold absolute pressure sensor is to measure the amount of vacuum we have inside your intake manifold and also boost or pressure if you have a turbocharged or supercharged engine all right so these sensors basically have a diaphragm inside of them and that diaphragm is moved up and down based on how much vacuum or boost there is inside your intake manifold and again similar to our mass airflow sensor we’re going to have three wires one of them is going to be our constant voltage the one ground third one signal as the static frame moves up and down it changes the resistance of this sensor the change in resistance translates into a varying voltage which is supplied through this signal wire back to your ECU all right now as far as how you can test these sensors we’ll start with the map sensor but first things first you want to make absolutely sure that there is no cuts in this vacuum line connecting your map sensor to your intake manifold next you want to get in your car put the key in the ignition and put it in the on position without turning the engine on next you grab your multimeter turn it on and you want to choose 20 volts on the DC voltage scale next you’ll ground your black test lead then remove the connector that’s going to your map sensor and then simply start probing these pins and the one that gives you any voltage that’s going to be your constant in our case it’s going to be this first one that gives us five volts so we’re going to put down this red one as our constant voltage supply wire next we grab our multimeter again and this time we’re going to change the settings to continuity and then we’re going to probe the two remaining pins and the one that gives us continuty to ground is going to be our ground wire a ground pin so here we go this third one is going to be our ground so there is red one is going to be a constant voltage this third one is going to be our ground so the remaining wire it has to be your signal light next you want to grab two paper clips and you want to back probe your signal and ground wires just make sure you get a good back probe in and they don’t touch each other or short to ground somehow by touching the firewall and whatnot so next you want to connect them to your test lead once again grab your multimeter put it to the 20 volt sitting on the DC voltage side and turn it on next get in your car and turn on the engine alright so as you can see at idle we got about 1.6 bolts now this is going to vary from you know vehicle to vehicle but you know actually if I’m not mistaken it’s supposed to be closer to one bolt and then as you open up the throttle and the vacuum goes down this voltage should rise alright as you saw the voltage didn’t

increase as you open the thrall so you could have a potential problem with our map sensor here now there is something that can make this go outgo alright so as you saw we were able to make this voltage go higher when we open the throttle plate quickly and closed it I think it’s basically it’s going to indicate a problem with our map sensor so when you’re opening your throttle plate slowly as the vacuum decreases it’s not returning to its position I’m assuming as quickly or as it should but when you do it quickly there’s a sudden drop of pressure or vacuum I mean then you can move back you know there’s more force you can move back a little bit quicker or I guess we could have a tiny crack in this vacuum line is coming from our intake manifold alright let’s see if we can find a vacuum leak all right so no vacuum leaks in that line so that makes it very likely that we have a bad map sensor here all right I’m going to call it a bad map since they’re here especially since I just remember something remember where we were testing the PCAT o2 sensor in my previous videos and it was showing very lean now when you think about it when this map sensor is stuck at 1.5 or 1.6 at idle and when you open the throttle plate letting a lot of air in that voltage is not going up telling your car the car’s computer that there is more air coming in of course computer is just going to assume that you know there’s very little air coming in so it’s not going to open the fuel injector as much therefore you’re going to have very little fuel all the while the throttle plate is actually open and there’s a lot of air going in so it’s going to cause a lean condition now I could be wrong on this but that’s my call as of right now bad map sensor on this causing a very lean condition on this car now before you replace your map sensor though it’s very important that you bench test it using a vacuum pump but we’ll save that for a separate video since this video is getting too long now as far as how it hits the mass airflow sensor well basically the same principles you get your multimeter you put it to the ground test it to the battery ground then you check for voltage first you should have told both for your MAF sensor and if you have one of those with the inlet air temperature sensor you’ll probably have 5 volts for that so you can separate that and then you switch it around and find your ground ground and then the remaining two are going to be if you have a 5 pin at the remaining two one of them is going to be for the temperature sensor the other one’s going to be for your the mass airflow sensor or you can always look up a wiring diagram if you have your car’s repair manual and find which words are which now if you want to see me actually testing mass airflow sensor using a multimeter I’m going to edit in cuts from a video I did about a year and a half ago on high tests of the mass airflow sensor with a multimeter right now alright so as you can see we got four pins on this wiring harness alright so the first thing you want to do is to find our constant voltage supply from our ECU so we’re going to get our multimeter turn it on and then turn our settings to 20 volts since we don’t expect to see anything more than 12 volts when testing for voltage next we’ll grant our black test lead next we’ll get in our car put the key in the ignition and turn the ignition to the on position without turning on the engine alright next we’ll grab our other test lead and we’re going to touch each pin and the one that gives us 5 or 12 volts we’re going to write down as our constant voltage supply wire all right here we go we’ll start with the bottom left you got nothing top left nothing top right and here we go we got 12 point 6 volts and there we found our voltage supply wire all right so nice we’re going to try to find out a constant ground wire and we do that by getting our multimeter and putting our settings to ohms and measuring resistance from each pin to ground and I’m going to choose this last setting on this multimeter which will not only give us a reading but also give us an alarm or beep whenever we have ground all right so while checking for grant you want to make sure you exclude the last pin which was our voltage supply wire because you don’t want to check the resistance of a Hotwire ok so we’re just going to start from the right bottom pin and work our way around and there we go first try we got it so our right bottom pin is going to be our constant ground wire so basically now we’re just going to reattach our connector and then back probe the two remaining wires and it’s not going to matter exactly which wire is which the other remaining tube because once you hook up our multimeter to that if we have them the wrong way around we’re only going to see a negative on the side of this but in order to get a more accurate reading if you get a negative sign next to our voltage reading all we have to do is just switch the test leads around and paper clips are great for back probing these connectors just make sure you get them in all the way and you press them in all the way and you make

good contact and next we’ll use these alligator clips to attach our test leads to the back cover connector since we’re going to be measuring voltage we go back to our multimeter and put our settings back over 220 volts all right so what we’re going to do next is to get in a car start the engine and then measure a voltage at idle at idle this car should have about 1 volt okay before I start the engine I think I need to mention that the readings I mentioned the 1 volt at idle for this car which is a 2001 f-150 with a four-point is that idle when the engine is properly warmed up now I’m going to be doing this on a cold start so the RPM is gonna be a little bit higher therefore it’s kind of a reading is going to be higher higher than one volt but then if it’s a good map sensor it’s going to come down decrease gradually and then sell it around more bolt there we go home salt alright so it’s been a couple minutes and it’s settle around 0.85 to 0.9 volts which is about right but now we just got it I’m just going to play with the throttle plate I’m going to slowly open it and we should see a gradual increase and the amount of voltage being put out by our math sensor and then once on the way down we should see a gradual decrease so that’s it remember folks if you have a lot of questions you have 36 hours after every new video I posted to my channel so the service actually is only provided to subscribers so if you’re not a subscriber I’m watching this make sure you subscribe wait for my next video when it pops up into your subscription feed click on it post your question it doesn’t have to be related to the whatever video I’m putting up that day and I’ll hopefully get to answer your question and if you don’t have any questions don’t forget to check out these other related videos on which I put links on the site and also in the description box alright thanks for watching I’ll see you