Clarification on the 5V Ref

Hello All-

I have a couple questions regarding testing the 5V Ref wires-

I was bored one day and looking around the web and came across a site talking about testing for bad 5V Ref wires using a small Amp Clamp meter. It stated that if you put your amp clamp around a 5V Ref wire at the PCM, that a good wire will show very little amps- (like .0001) and a wire that is not good will show much more? I have not tried this yet, but was wondering if this can be done and is it accurate. Im not that experienced with the whole electrical testing theories and know that their is a wealth of knowledge from people here. Can you guys elaborate on this and maybe clarify some stuff.

Thanks Much,
Mr Mike

Interesting concept.
I don't know about your amp clamp but mine struggles to accurately display in the hundreds of miliamps, let alone tens of miliamps.
I think voltage testing is going to stay at the top of my list for reference voltage circuit testing.
With a very $$accurate$$ clamp, it may be a useful test to identify a shorted reference circuit.

This test is really only good to differentiate between a shorted 5v reference and a pcm that's either dead or not powered up causing low voltage on 5v reference

Sent from my SM-G781V using Tapatalk

5v ref circuit faults fall into four main types
(1) Voltage pulled down by a shorted sensor.
(2) Short in wiring
(3) Open in wiring --- break or connector contact issue
4) Open internal to ECU ---- burned out or bad soldered joint ?
(5) Short inside the ECU --- think water ingress ?

As already suggested most DC amp clamps really aren't that useful at the low end of the range so it really boils down to looking for wiring and connector damage (visual first only then tug test), disconnecting sensors. For suspected breaks in wiring you should pierce the wiring and do a voltage check.
If the above give you evidence to strongly suspect an internal ECU issue cut a break in the wire close the ECU (which you splice back later) and voltage test.

Thanks you guys- Sounds like the DMM is best tool to use. Just another 2 quick questions. I have those wire piercing probes that break the wire insulation. Is it fine to leave that small hole in the wire after checking? Also, as far as the 5V Ref- If I were to locate the easiest sensor-(i.e. TPS) to check the Ref voltage and this sensor 5V Ref also feeds a few other sensors- The reading I get at the TPS should be the same at the other sensors hypothetically?

Your question about wire piercing might start a religious war.....


It's best to seal it afterwards, you could do so even with nail polish if nothing else is around.

Second question is yes, but the 5 v may not get to a specific sensor if the circuit leg had an open.

Back in the 90's a single 5v Ref was often shared between all sensor but because most cars these days have so many sensors that require a 5v ref the engine computer may have two or three independent 5v ref sources, the wiring diagram may or may not give a clue as to the 5v ref arangement within the engine computer.