Can I use a LoadPro on the two 5v signal wires of MAF?

I'm assuming I can but I sure dont wanna try without confirmation as I learn the basics.

Can I use a LoadPro + terminal on the two 5v signal wires of a MAF to test for voltage drop (circuit integrity)?

Or is back probing the MAF connector KOEO and seeing a 5 volt signal proof enough? 

I'm seeing varying Air Mass Flow Filtered (KG/H) on scan software so I know its changing with throttle input.

loademup ( ), I believe the short answer is no. If you were to apply the LoadPro to a 5V reference circuit, it would very likely pull the reference all the way to zero or close to it.

The reason is the resistance of the LoadPro itself. I forget what the exact value is, but it's not much. Less than 50 ohms, IIRC. On a 12V power/ground circuit, that's a reasonable amount of load. On a 5V reference circuit that is not built to carry load, less than 50 ohms amounts to a direct short to ground. For comparison, my rule-of-thumb for 5V reference resistance to ground is >5,000 ohms.

IMO, a backprobed voltage reading at the MAF with the sensor connected like you described would be perfectly fine.

Thanks for your help! So essentially the digital signal wire is not a candidate for a voltage drop test because it would drop to zero but not indicate a bad wire?

But would that damage the ECM? I assume not since their would be no runaway current.

So really for a MAF, the signal wires must be tested with an o-scope?

loademup wrote:

Thanks for your help! So essentially the digital signal wire is not a candidate for a voltage drop test because it would drop to zero but not indicate a bad wire?
 

No, signal wires (and other 5V reference circuits) are fine for voltage drop testing, in the basic sense of the concept. Measuring voltage at different points in the circuit with the load present and the circuit working.

Someone could argue that, if using the LoadPro on a 5V reference circuit can pull it to ground, then the wire MUST be good. Otherwise, how did the circuit go to ground? But I feel that test is probably overkill. And anyway, you could use a jumper wire to ground and achieve the same thing.

But would that damage the ECM? I assume not since their would be no runaway current.

SD shorted a 5V reference to ground with his ammeter in at least one of his videos, I think. Measured somewhere around 300 mA.

Would it damage the ECM? I would say that it shouldn't, but I wouldn't count on it. I've seen a bunch of shorted reference circuits, and accidentally done it during testing more than once. Never saw a damaged ECM as a result. But I still wouldn't encourage anyone to go around creating 5V reference shorts.

So really for a MAF, the signal wires must be tested with an o-scope?

No, I think a normal multimeter would be just fine. A graphing meter or a scope would absolutely be beneficial if the problem is intermittent, or if the signal is very fast. I've also found it's easier to understand what's happening in a circuit you're unfamiliar with if you use a scope, just for the visuals. But a scope is not strictly needed.

Interesting!

So they how do you test signal wire/circuit integrity if its not 100% safe to use a Loadpro or test light to do that?

I assume that if you backprobe the signal wire while KOEO and get the requisite voltage then it must be a good wire all the way to the engine computer?

I'm such a NEWB!!! Thanks for the help.

The best test, in my opinion, for a signal circuit like you describe is to watch the data PID for that sensor, say MAF voltage, and jump 5v into the signal circuit. If the PID on the scanner goes to 5v, then the circuit is intact amd the computer is still smart. If when disconnected the signal voltage is high (5v on a pull down circuit), then jump it to ground and watch the data PID to also display ground voltage.
As Tyler said, there's really no advantage to using the Load Pro on anything other than battery voltage. Great for finding voltage drop in electric motor, solenoid or headlamp circuits, not so much for anything else.

I really appreciate you guys teaching me.

I didnt find a way to track voltage of the MAF signal wire on my Bimmer Protool software or Autoenginuity but I did track its results: Air Mass Flow Hfm (KG/H) before and after air filter and it did change with throttle position, for whatever that's worth.

Dont know if that is enough verification of normal function without an o-scope.