2001 (5VZ-FE) EFI-1 fuse cooked. _HelP_

Hello!
The fuse is completely gone. Burned away fortunately not causing a catastrophic fire.
We may need a new engine relay/fuse box unless there is a bypass solution.
Been searching around here for clues about what others have done in this situation.
Download and digesting the 2001 Tundra EWD429U to diagnose the cause but figured a post might help.
Posted in ‘Electrical’ but our trucks are antique so maybe we think differently in here.
Thanks!

 

The main cause if not the only cause is due to overly corroded negative battery terminal and cable. That Neg battery terminal corroded that bad is causing increased resistance thru out the system degrading the battery prematurely, causing HIGH current draw.
I would consider stripping the insulation back on the negative cable 3 or 4 inches(red circle) and if corroded as bad as it appears as seen in the below pic, I would suggest changing the neg cable also.
Not properly rectified and you'll prematurely need a starter, alternator, battery....etc.
Good to have the EWD but no EWD needed to diagnose that lack of maintenance.

 

I don't think there's a safe way to bypass it. You're going to need a new fuse box. The bigger issue is, what caused that EFI circuit to overload? Was there a problem and someone put in a fuse with a higher amperage rating to keep it from blowing?

 

@BubbaW you're a sight for sore eyes. Your presence was missed!

I have to agree with Bubba on the cause and ATBAV8 on the solution: You really need to replace the fusebox. I'd start hunting JY (junkyards) for your year/cab type and get a new box, with all fuses and such. Test for continuity on the circuits before you install the new box. Bonus here is simple: You now have several very-expensive relays and some fuses as spares after, and you hopefully won't be worrying about another meltdown.

I can't imagine you'd pay more than $100 for a fully populated fuse/relay box from a JY

 

My first mouse click found this...I'm sure there are many more to be had.

https://www.ebay.com/itm/2762304222...N5aDRgixAkd3g2SwOP_BzVGaKakjIhn1X0xUeS-pM8mW4

 

Wao, thanks! Solid intel.

Truth Bomb. _Embarrassing. All I can say is, we acquired the truck last summer and I skipped basics for a host of other issues. …Terminals, duh. First thing.

Based upon other evidence of neglect the wrong fuse is possible. Also, read somewhere that a stressed fuel pump draws more current, filter looks original. Maybe this combines with the first thing .

This is the way, yes. The bonus of a ’populated’ box is preferable.
Sometimes however an unsafe bypass helps us get from here to there, in case anyone has experience in those matters.

Thanks! My search only turned up the V8 variant. Maybe because this seller doesn’t ship to ‘protectorates’ and we are on one. We’re hoping they’ll make an exception. Junk Yards are literally an ocean away.

~~

 

The truck stalled away from home base when the meltdown occurred.
The immediate plan was a bypass to get moving but I got lucky and was able to clean the area enough to stick a fuse in there and get her running normally. Ugly as hell, yet functional. Drove home beautifully.

Monitoring the 15A EFI-1 fuse with a temperature gun, it leveled around 110-120*F at idle. Is that normal operating temperature? The EFI relay at the lower left corner of the box was around 130*F. Wondering if that relay triggers any operation which can cause higher temperatures along the circuit. I have no idea.

While sourcing an uncooked relay/fuse box I’ve been looking for guidance on how the wiring is connected to it.
Doesn’t seem to be a nice series of clip harnesses. Probably figure it out with the donor part in hand but was wondering if there was magic or special tools involved.

 

Good morning all,

Quick question regarding the circled ground. What purpose would this ground have and what would be the result if this were accidentally removed and never put back?
I have an '02 Tacoma with the 5vz also and remember a long time ago accidently yanking on that wire and it's never been replaced to this day. No electrical issues this far, that I know of.

 

It's essentially grounding to chassis. The other grounds to the block, IIRC. The kinds of things it would impact would be anything that's grounded to chassis, ultimately. Something like that line not being connected could lead to electrical gremlins, flickering lights, weak ignition, retarded starts, weird idles, etc. especially for people in rusty climates. If it were me, I'd replace it.

Understand a lot of grounding in vehicles is redundant, for the sake of fail-proofing. Doesn't mean you should be OK with leaving a ground disco'd.

 

Thank you! I will do just that than. Currently rebuilding/replacing the engine so that'll be added onto the list among many other items.

 

Hey, got lucky.
Shallow corrosion.

 

Do yourself a favor. I see you have terminal pads on the posts so smear a little grease on the posts to prevent recurrence.

 

Good advice. A little goes a long way. There’s petroleum jelly all over that action.
… Pads are leftovers from the PO.

So the replacement used relay/fuse box is boarding a ship to cross the ocean and arrive around the 26th.
The engine ran today for an hour without warming the fuse past 125* F and I’m seriously considering not tearing apart ALL the factory circuits to replace the single cooked one. Especially since the cause is still a mystery.
A buddy who knows more than I do is kindly going to help with multimeter testing on the circuit.
I cleaned (and greased) the ground for the EFI circuit which is directly next to the battery terminal ground on the fender. Next we’ll check continuity, resistance, etc. ~

 

across the ocean?!

The pads are a good thing, they actually work.

I think you’re overestimating how difficult swapping that box is. It shouldn’t be more than a harness and a few larger wires. I don’t believe each fuse has a circuit you need to connect. The hardest part with them is typically getting the box out. Consult the FSM or maybe YouTube.

 

In case anybody’s wondering what’s underneath your relays/fuses…
2 Harnesses and countless individual wires. [5VZ-FE] 2001

 

We opted for the less intrusive solution for now and will continue to monitor the temperature.

 

Update:
The Tundra ran fine for around a year then our fuse bypass melted. I monitored it for months, saw no change and figured the fix was good. Maybe it waited till I looked away. So I replaced the melted bypass with another one and decided to chase this Gremlin while continuing to monitor the fuse.

Recently, the CEL lit up a P0171 code. I cleaned the MAF sensor but the code returned. Checked for vacuum leaks and found none. On two occasions the engine idled roughly and had no power only to run normally the next day.

Since we’re in the future now, I fed the Toyota Electrical Wiring Diagram Manual EWD429U to an AI assistant and asked questions about the EFI circuit. During this process, I was checking the state of the upstream oxygen sensor (

$149 Denso 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

Denso 234-9001) and detected continuity and a 1.1ohm reading between the two black wire pins. The AI assistant concluded this was evidence of a short circuit and the cause of the cooking EFI fuse. Having a ‘97 4Runner with the same engine, I checked the oxygen sensor and detected 13ohms across the black wire pins. That was it!

Until I tested the new replacement oxygen sensor before installing it in the Tundra and found the same 1.1ohm reading.
Apparently the sensor for the Tundra is an “AF” sensor which runs 1.5-3ohms. Maybe the new part is DOA. The AI assistant is unclear on the specific details of the oxygen sensor but seems to think 1.1ohm is too low and would generate heat at the fuse.

I installed the new oxygen sensor yesterday and the truck runs fine today but the P0171 code remains.
After 30 minutes of driving the EFI fuse bypass read between 140º and 145ºF.

Any humans out there have access to an upstream O2 sensor for a 5VZ-FE in a 2001 Tundra (Denso 234-9001) and could confirm this ohm reading or can direct me to a source?


Thank you

 

I can do some checking when I get to the shop on Monday. Tag me if not answered by anyone else by Monday to remind me.

 

First and foremost, AI has improved drastically in last few years but this time Mr or Mrs AI failed ya.

Can't speak about 4runner and their sensors but the oxygen sensors for 5VZ or 2UZ and 00-04 Tundras, the 2 black wires of our Denso oxygen sensors are for the sensors Heater Circuit. It's simply a heating element no different than a dryer heater element. It helps to get the sensor HOT so we can go into closed loop quicker. It's true some folks refer to upstream as Air/Fuel sensor, which in a way that's not wrong. It's reporting to the ECU what air/fuel ratio is. However, true A/F sensors did not come about till 05 Tundras where they changed it to a planar type to improve on heat conductivity.

Speaking of your 01 5VZ only, a resistance measurement of the Denso 2 black wires(+B and HT) are good at 1.5-3 ohms according to what ambient temperature is. The white and blue wires of the sensor can not be measured the same, an actual OBD scanner capable of reading live data in particular the sine wave pattern it would show when in system.

From FSM....

 

Excellent. So the new O2 sensor is fine and so was the old one as far as the measurable heater circuit. Thank you for the FSM information, those were exactly the specifications we needed.
Tomorrow we’ll check the status of the MAF sensor.
…The quest continues…
It’s fun to play with AI but there is no substitute for human kindness.

 

Update:
P0171 has been gone for a week, since replacing the MAF due to ‘under reporting’.
The temperature of our EFI bypass fuse remains between 130º-150º, ambient engine bay temperature.
AI mentioned that the MAF could be causing that fuse to cook but this has not been confirmed.
‘Big Dog50001 Automotive’ has an excellent P0171 video on YouTube which helped me understand how to read live data on a code reader, specifically relating to fuel trim.
Highly Recommended:

https://youtu.be/SugtR4KMIDU?si=GYeZObyb90ZsrZod

 

Automotive wiring will heat up and pop fuses due to corrosion in the wiring, actually inside the jacket. Corrosion inside wiring casing is a bit of a known issue with these trucks. there are quite a few pics of it here on the forum.

 

Yeah, my moneys on AI failed ya once again because MAF feeds info to ECU.