ECU Voltage

I did some more investigation today and I think the instrument cluster has a failed diode or similar. I don’t think the issue is with the fuel gauge itself but more than likely with a different circuit on the same power supply at the fuel gauge.

A new one is $361.20 from my local Toyota dealer but before I make a move on that I may take the dealer up on their $115 diagnostic procedure. I’m hoping their equipment can tell me if the circuits in the instrument panel are faulty.

 

Dome light supervision circuit

 

With the door closed and the door switch installed and with the door open and the door switch uninstalled there will be ~+11v on the door switch wire. +12v goes through the dome light and the dome light's bulb acts like a resistor which drops the voltage from 12v to ~11v.

Does your truck have an aftermarket alarm or keyless entry?

 

Door open indicator lights and the fuel gauge are in the cluster, I wonder if they're tied together somehow in the cluster...

 

That makes perfect sense, like I said closing the door had a direct effect on the voltage at the pump connector. The weird part is, inside the truck with the doors closed and no voltage on the fuel sending unit wire, I can turn the key on and the voltage comes right back. It’s like the dome light circuit is backfeeding the the fuel gauge sensing wire. I’m about 90% sure I pulled the dome fuse with no change though. I know for a fact that I pulled the dome light bulb with no change in voltage at the pump connector.

Really sounds like a bad diode or 12v+ bus bleed over from the cluster.

For reference, my door ajar light works perfect.

 

No aftermarket alarm, just the factory keyless entry. You’re exactly right about the voltage, when I removed the door switch it had the exact same voltage as pin 2 of F19! Sounds like we’re getting somewhere!

 

Me too! I also wonder/doubt if Toyota can tell me if the dash if fried in an expeditious manner?

I’d pay $100 to know that spending $360 would fix the problem. Just don’t want to spend $360 for nothing.

Also, hopefully some of those on here with janky gauges can check their wiring too and see if there is any voltage on the supply wire for the fuel gauge. It only takes a couple minutes to pull the door jamb and kick panels to disconnect connector ID2 and probe the orange wire at the bottom left!

 

Driver's side kick.panel correct?

 

Correct, ID2 is a square looking connector behind the drivers side kick panel. I unplugged my ID2 connector to read the open circuit voltage. Leaving it connected would include the resistance value of the fuel level sending unit!

 

Dude, you are REALLY overthinking this. If you disconnect the dash and the voltage goes away you got a bad cluster. Easy. If you want to confirm go get a used unit and plug it in. If the level is now correct, you have your answer.

 

That's what I was thinking, pay via PayPal and just return it if you don't need it.
It really sounds like a cluster issue to me. I mean gas gauge + door switches = cluster. Idk maybe there is a rat problem where he lives or a rust problem idk

 

0.000v on the side with the female metal contacts and male plastic connector.
11.44v on the opposite side. Key off door open gas tank and wallet are empty lol

 

So you have 11.44v on the gauge side of the connection with the key off? I don’t have my truck disassembled right now but the side reading 0v should be the tank side and the side reading 11.44v key off would almost certainly be the dash side of the ID2 connector.

Does your fuel gauge work accurately?

 

Everything on my truck electrically and otherwise is clean. If you're laying on your right side on the door sill plate looking at the kickpanel are after you removed the kick panel and you use two hands to disconnect the plug put your right hand on the half of the plug furthest away from you and your left hand on the side closest to you, 0.000v in your left hand 11.44v in your right hand.

 

That’s what I thought you meant.

Since your readings mimic mine within .2v and your gauge works, I’m thinking that perhaps this is somehow in the design for the circuit and my problem may lie elsewhere.

I may not have been clear but when I first connected the new Toyota sending unit to connector F19 my gauge worked perfectly. The lowest position on the fuel level sensor arm read below empty on the gauge and the low fuel level light was on. Fuel read full on the gauge and half read half.

It was after testing for a couple minutes that my issue with the gauge reading 1/8-1/4 when the arm was all the way down reappeared.

I don’t see what could’ve changed.

 

Every time I tested the gauge alone by Toyota’s method in the FSM. It tested flawlessly.

 

Does this mean your fuel gauge works? F on full and E in empty? Do you ever run the tank down till the low fuel light comes on?

 

Thank you very much for taking the time and effort to check this on your truck, you may have saved me $361 dollars if the issue proves to be somewhere else!

 

Yes
Yes
Yes, unfortunately

 

I'm really leaning towards the cluster... but... my battery voltage and my OBD2 voltage match perfectly and yours doesn't. I think there's more than one problem. I don't really know anything about your truck, I'd take a serious look at the battery cable condition by slicing into the insulation maybe a half inch peeling it back and looking for corrosion, I'd inspect every detail of the fuse box on the underside where connections occur, I'd follow every inch of pertinent harnesses with my hand looking for anything and then I'd order a instrument cluster via PayPal. I'm a retired DC electrical specialist and shit has changed and I haven't needed to keep up. I've rewired hot rods, boats, all kinds of stuff. But 2nd gen Tacomas? No.