2G Testing, fuel assembly/gas gauge.

[miliman13]

Before you go buying a new dash gauge (or at least in addition) you should also make sure the senders and wiring are working as they are normally connected in series to ground. Unplug the driver's side fuel sender 4 pin connector. Connect your ohmmeter to the harness side all yellow wire and the other ohmmeter probe to a metal ground (no need to turn key on). Make sure the reading is between 4-107 ohms depending on how full your tank is (4=full, 107 is completely empty). If you don't have this you also have a sender/wiring problem independent of any dash gauge issue.

A little confused now. I thought that's what I just did in the previous post.
In the image I'm testing resistance on solid yellow wire and grounding to chassis.

But I thought that measures the gauge...

 

[luv2rallye]

I'm sorry. Yes you did. I told you wrong. I meant to say test the senders side. So connect the ohmmeter to the drivers side, sender side connector (not the harness side) solid yellow wire (other ohmmeter probe to ground). You earlier tested each sender separately but I don't think you tested them all connected (which is what the gauge sees) which would be good to double check.

 

[miliman13]

With the "passenger side harness connected" i tested the "drivers" side sender bottom right pin/Solid yellow pin and i get "Infinity" with key not in.

 

[luv2rallye]

That is NOT GOOD. You need to troubleshoot using the wiring diagrams in my post 8. You have an open circuit somewhere.

 

[miliman13]

at least its not a short!!!

Since its the sender that has infinite resistance, doesn't that suggest the drivers side sender is bad ?
How could that involve the harness in the car?

 

[luv2rallye]

By probing the drivers side - solid yellow wire - on the sender side 4 pin connector half; you are testing resistance of the ENTIRE circuit [ohmmeter's negative (black) lead must be on a body/chassis metal ground]. Follow my wiring diagram in post 8 (fuel sender wiring 2g.pdf) to see the following: The ENTIRE circuit is the drivers sender itself (solid yellow on 4 pin connector), the wire from the driver's (4 pin) sender to the passenger (6 pin) sender (one of the yellow/blacks), the passenger (6 pin) sender itself (the same yellow/black), and the wire from the passenger (6 pin) sender to ground (solid black). So if you read infinite, the open can be in any one of them. Just move your probe down the line (towards the black ground) to find the open.

If you already know the open is in the drivers sender then your done and need to replace/fix it. But it didn't sound like you knew for sure, and then we got off into testing the dash gauge. I didn't want you replacing the dash gauge without further testing the entire sender circuit in case you have 2 failures.

 

[miliman13]

Cheapest gas gauge yet... probably the most accurate

https://www.amazon.com/DROK-Resista...sr=8-20-spons&keywords=resistance+meter&psc=1

 

[miliman13]

By probing the drivers side - solid yellow wire - on the sender side 4 pin connector half; you are testing resistance of the ENTIRE circuit [ohmmeter's negative (black) lead must be on a body/chassis metal ground]. Follow my wiring diagram in post 8 (fuel sender wiring 2g.pdf) to see the following: The ENTIRE circuit is the drivers sender itself (solid yellow on 4 pin connector), the wire from the driver's (4 pin) sender to the passenger (6 pin) sender (one of the yellow/blacks), the passenger (6 pin) sender itself (the same yellow/black), and the wire from the passenger (6 pin) sender to ground (solid black). So if you read infinite, the open can be in any one of them. Just move your probe down the line (towards the black ground) to find the open.

If you already know the open is in the drivers sender then your done and need to replace/fix it. But it didn't sound like you knew for sure, and then we got off into testing the dash gauge. I didn't want you replacing the dash gauge without further testing the entire sender circuit in case you have 2 failures.

Wait, this test does it have to be performed while the sender ( driver side) is connected to the harness as well? because it wasn't connected thats how i was able to probe it and test resistance.

 

[luv2rallye]

No, initially the drivers side is not connected but the passenger side must be. If you work on down past verifying the drivers side is ok, then you'll unplug the passenger side to test it.

 

[luv2rallye]

Cheapest gas gauge yet... probably the most accurate

https://www.amazon.com/DROK-Resistance-Back-light-Motorcycle-Automotive/dp/B00D42KA4M/ref=sr_1_20?ie=UTF8&qid=1471576540&sr=8-20-spons&keywords=resistance meter&psc=1

You do realize this outputs resistance - not gallons.

 

[miliman13]

You do realize this outputs resistance - not gallons.

?? Yes of course, isn't that evident?
As we have discussed a fuel gauge simply reads resistance. And since i have found full, half and empty readings this meter would prove highly accurate i suppose.

 

[miliman13]

i know its not pretty but i cant seem to win...
I took one course: circuit analysis Ac/Dc Intro.

And i can't really read the PDF

But if passenger is connected and not drivers side and this is a series circuit how is the unplugged sender connected, if its unplugged how am i reading an open circuit in the harness.

 

[miliman13]

What i mean to say is.... for example
I replaced coil packs on an infiniti G35 because I 1. unplugged the connector from the coil and 2. tested infinite resistance.

When the coils are good they will have "some" resistance.

Aren't i essentially doing the same here? if i unplugged the 4 pin connector on the driver's side and test the sender and read infinity, then isn't the sender the issue?


I understand the difference between series and parallel , but my low level gas icon works.
Shouldn't it not work then if its an open circuit

 

[luv2rallye]

Oh oops - my age is showing. Yes, sorry, the drivers connector is unplugged so you can only test the sender itself since it's no longer connected to the passenger sender, dah - I feel like an idiot! So disregard everything I've said when having the sender unplugged other than testing the sender itself.

Ok so you'll have to figure out which yellow/black (use one on pin 1 - not pin 4 which is the level switch) goes to the passenger side and probe it (to ground) to see if there's resistance.
Thanks for the correction.

Could you read it if I put the diagram in a Word file?

 

[PlanZero]

Dude my head hurts after reading this thread. I had this happen on a GS years ago and I just reset my trip meter every time I filled up after figuring out how many miles per tank. After reading this if it happens on my Tsi awd I'm doing the same. Sorry to interrupt your discussion!

 

[luv2rallye]

You should see my head now. Embarrassing, I don't usually make gross errors like I have in this thread.

 

[miliman13]

Dude my head hurts after reading this thread. I had this happen on a GS years ago and I just reset my trip meter every time I filled up after figuring out how many miles per tank. After reading this if it happens on my Tsi awd I'm doing the same. Sorry to interrupt your discussion!

, no problem.

Oh oops - my age is showing. Yes, sorry, the drivers connector is unplugged so you can only test the sender itself since it's no longer connected to the passenger sender, dah - I feel like an idiot!

Ok so you'll have to figure out which yellow/black (one on pin 1 - not pin 4) goes to the passenger side and probe it (to ground) to see if there's resistance.
Thanks for the correction.

Could you read it if I put the diagram in a Word file?

Ill test tomorrow my old self gets tired when i stare at a screen for long.

And i ment i can't comprehend, when i said i can't read it. I can analyze only the most basic circuits. You know r1+r2+r3....... = rTotal

 

[miliman13]

You should see my head now. Embarrassing, I don't usually make gross errors like I have in this thread.

I guess i have that effect. I didn't believe you could have been mistaken, i immediately accepted blame. And read the thread, again.

Again thanks for the patience.

 

[luv2rallye]

I can analyze only the most basic circuits. You know r1+r2+r3....... = rTotal

Well r1 is the drivers sender and r2 is the passenger sender. r1 + r2 = rTotal. And rTotal should be in the 4-107 ohm range depending on tank fuel level. Of course they have to be plugged in.... [To test the solid yellow with everything plugged in I stick a sharp pin through it's insulation.]

Ya the diagrams in my post 8 can be confusing. Page 203 shows the two senders but what they assume you know is that:
1) F/GA is the dash fuel gauge
2) "sub fuel gauge unit" is the drivers side sender
3) "fuel gauge unit" is the passenger side sender
4) Connectors E-39 (4 pin) and E-59 (6 pin) are shown at the bottom on page 202 but it's unclear which way (direction) they're looking at them. In this case it's supposed to be the male side but I've seen even knowing that, sometimes it's looking from the flat connector end and other times from the wires end using the same exact male side symbol (I've given up believing which since they're not consistent with their own representation). That's why I always just say the wire color.
5) The number next to the connector wire is the pin number.
6) For wire colors B=black, Y=yellow, Y-B is yellow with a black marking (usually a stripe or ring)
7) There are two Y-B wires on each connector so it's easy to get them mixed up (the other is the level switch on E-39 pins 3 & 4 and the thermistor on E-59 pin 3).
8) The ground point (big white on black 8) next to the ground symbol is the physical ground connection point under the driver's seat.
9) Keep in mind wire colors fade with age.

I've had enough. I'm going to bed before I make another fool of myself.

 

[miliman13]

Using a needle to prove the connector while plugged in I tested in this order

Top right, top left, bottom left, and bottom right.

See pics.

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This is both sender's connected key off

 

[luv2rallye]

Ok the 4 wires should be Y, Y-B, Y-L (L=blue), another Y-B. Please tell me which is which (using top right, top left, etc).

 

[miliman13]

Ok the 4 wires should be Y, Y-B, Y-L (L=blue), another Y-B. Please tell me which is which (using top right, top left, etc).

Bottom right is solid yellow.
Top right is yellow/black
Top left is yellow/blue
Bottom left is ???

 

[luv2rallye]

Well they all have acceptable values except the top right at 89 ohms. This should be pin 1 that goes between the two senders (Y-B) which essentially is measuring the passenger sender. Since the passenger sender is spec'd at 2-57 ohms I suspect it has worn or perhaps is stuck in a higher resistance place at the moment or just bad. If stuck that could explain running out of gas when the gauge is not at empty. Senders getting stuck are not uncommon when they go bad. When they stick they can be anywhere. So just because it's higher resistance now (which should say empty), doesn't mean that's where it stuck when you ran out of gas. You could remove it to see if it is stuck and try freeing it up. However you'd risk it happening again.

As a double check on the resistance value, I'd disconnect that drivers side connector and probe (to ground again) that pin 1 (Y-B) top right pin on the harness side (which goes to the passenger side so this time it can be disconnected). If higher than spec try bumping the passenger side sender tank cover to see effect of vibration.

 

[miliman13]

^ I did double check/ ground that pin just in case.


No change. At this point an after market gauge/meter will be the most economic, and least time consuming.

It would be near impossible to find a replacement.

I'll update the ohm meter and how it's used in conjunction with the thermistor.

Rally thanks again, you are one dedicated member/ Wiseman.

 

[luv2rallye]

Ok sounds good getting a new gauge. Just remember you may also have an intermittent bad passenger sender which would mislead any new gauge. So if you run out of gas again you'll then have to replace that sender.