MAF, O2, low voltage, fuses good

Hello all, sorry for long post.
2005 DC Limited 4x4 170k miles.

I am having a strange electrical issue that I can't seem to figure out. I suspect it may be inside the fuse block under the hood, but I'm not certain.

On occasion the truck would start, then die immediately several times, then start and run OK, but still stumble under hard acceleration. Then 30 min later, the truck would start fine, and run fine.

It started as a rare (every 3-6 months or more) occurance has progressively gotten worse. Down to once a week, to now it's stuck permanently in "start then stall" mode.

CEL comes on with low voltage on Maf, O2 sensor heater circuit, and purge valve stuck open.

After research I found that many people had a blown efi fuse caused by o2 sensor wires. My fuse is fine though, and shows full voltage, along with the relay. And the o2 wires all look fine from what I can tell.

I tested voltage at the Maf sensor power wire, and only getting .4 volts. After some fiddling, I realized if I pushed amd pulled on random fuses and relays while the truck was running, I could get the power back to the Maf and purge valve. I could hear the purge valve click, and then the Maf would start reading again according to obd scanner. This worked for a while, but eventually it stopped helping.
While the issue is happening, the Maf reads constant 1.43 g/min even when revving engine.

Today I decided to take the fuse box apart, hoping to find an issue with the efi circuit, but it didn't go as planned. I was able to separate the top and bottom of fuse box, but didn't expect all the different plugs on the bottom, that don't match up with the relays and fuses like I hoped they would. So I assume there is some sort of circuit board type system in between the fuse and relay sockets, and the plugs on the bottom of the box.

After that I decided to try an experiment, and run a new wire directly to the Maf with battery voltage. Initially, I left the maf wire together, and just tapped into the side of it. This did not change anything, so I cut the factory maf power wire, and left the new wire attached to Maf.
This caused the Maf to start working again. It started reading different values that went up if I revved the engine.

The truck started fine several times in a row with the new power wire connected.

That's where I am at now. The new power wire was just an experiment, to make sure the Maf was still working, but I still need to figure out why the efi circuit has low voltage, but tests fine at the fuse box. I would assume a short in a wire somewhere, but I figured that should blow a fuse. Also the fact that pushing on the fuse box helped the issue slightly, makes me think the issue might be in there, or close by.

Any help would be greatly appreciated.

 

You're going to think I'm full of shit, but I suspect this is probably your problem, as it has been the problem of so many others: https://www.tundras.com/threads/1st-gen-psa-clean-your-battery-terminals-you-lazy-sods.131635/

 

I’ve also noticed Tundras are more susceptible to weird lights/codes when battery is bad or terminals/cables corroded. Follow Shifty’s advice

 

And just to add to it: if it’s not the cables I would be checking all the grounds in the engine bay. The one from battery to fender wall, back of block to firewall, the one at the front of the drivers side coil over and I’m sure I’m missing a couple more.

 

Thank you for the advice. Definitely not full of shit.
I suspected the same thing originally, because the secondary cable coming off the positive terminal (going to fuse box) was slightly loose when I first had the issue. I cleaned and tightened it, and the issue seemed to go away, but it came back a few months later.
Both of the terminals look pretty good, no buildup at all. I have cleaned them thoroughly anyway, and tightened them as much as possible. I also checked, cleaned and tightened all he grounds. I even went as far as adding am extra ground cable from the firewall to the engine block, to see if it helped.
Also I replaced the battery a year ago, with a platinum die hard.

The voltage has seemed a little low a few times. When I didn't drive it for a few days because of this issue, the battery read 12.1 volts. With cold weather I didn't think much of it. When it does start, it runs 13.8 or so, but the maf still has the same low voltage.

Maybe I will try starting it with a jump box connected, and see what happens. The battery might be weak already. Makes sense with the problem getting worse over time. Maybe new battery cables all together.

 

Sounds like you had some parasitic drain going on there, batterywise. I know this will sound like a weird question, but do you have a bluetooth OBDII dongle attached, or actually, anything attached to the OBDII port?

Have you measured voltage at the MAF itself?

Can you get us the laundry list of codes, so we can think back through circuits?

This is another one of those cases where I wish @BubbaW was around. He had a natural gift for circuits, I think he'd probably see the list you put in your 1st post and immedaitely find a common point.

 

Thank you for the reply. I actually do have an obd Bluetooth adapter plugged in, and have left it plugged in for a while now, since i was monitoring the maf signal. I didn't think about that, but that could be discharging the battery.

The voltage at the Maf was only .4 volts, both with the vehicle running and not.

I will have to read the codes again later today when I get home and post the actual code numbers, but they were Maf and o2 heater circuits low voltage, purge valve stuck open, and evap system valve.

The codes all do seem to have a common fuse from what I have read, the EFI2. Others have had the same exact issue as me, but their fuse was blown, usually due to an o2 sensor wire rubbing on the heat sheild. My fuse has never blown, and I have replaced it, along with the efi relay, trying to fix the problem. All my heat sheilds are still attached and the o2 wires look fine.

One of the reasons I think it might be a short, and not battery related, is because when I jumped the Maf sensor power wire, with a wire straight from the battery, the maf still didn't work. But, when I cut the factory Maf wire completely, it started working with the jumper wire.
So it seems like there is a short somewhere on that circuit, but it's not bad enough to blow the fuse I guess.

I need to figure out where the power wires for the maf, o2 sensor heaters, and purge valve all come together and enter the fuse box, then I could test each wire for a short and find the problem area. Thought it might be obvious when I opened the fuse box, but it was not.

 

Check the attached PDF, in the dash connector J47/48 is the connector where all of that is routed through.

 

@Festerw thanks for that.

If that's the case, J47/J48 being plugged into the back of the in-dash fusebox and controlling all those circuits could mean @Br1124 may be suffering from the dreaded green rot talked about in the megathread. Specifically:

• These trucks usually don't have a ton of other electrical issues. Hidden corrosion inside the battery/alt cables happens. Sometimes, a couple thousand miles after timing belt changes, people will have startup issues because the crank position sensor wasn't properly tucked away and gets rubbed by a belt (pic). There's also a similar problem with camshaft position sensor under the cam cover, where the belt will rub through (pics). There's the rodent issues mentioned earlier. Occasionally, water leaks can send water down into the ECM behind the glovebox (pics), or into the fusebox inside the cab/dash (pics & pics & pics, it happens a LOT). Many drain/vampire issues trace back to aftermarket add-ons whether the owner knows they exist or not - alarms as mentioned earlier, brake controllers, poorly installed trailer receptacles, those are some big ones.

​

Wondering if a cracked windshield, rotten windshield frame, or an A-pillar leak may be at play here....

I would've expected those specific sensors to get power via the engine bay fusebox though.

​

 

The power does indeed come from under the hood, EFI Fuse 2. I can't say the entire routing but this is just where the first connector off of that is located.

 

Thank you guys for all the input. Yes the power does come off the under hood fuse box, but for some reason, the wire diagrams do show the j47/j48 junction box on the "in cab" diagrams, and not under the hood.

It appears to be somewhere behind the in cab fuse box. I went digging around, but wasn't able to find that junction under the dash. 2.3 million wires under there. There are a couple of junctions on the back of the engine, which would make more sense, since it's supposed to go to the o2 sensors, but who knows.

Update though, when I initially tried to jumper the Maf, and left the factory wire connected, there was still no power to the maf. When I cut the factory wire, and only used a jumper to the Maf, it started working again. However today, I decided to reattach the factory wire, with the jumper wire, but remove the efi2 fuse from the box.
This time the Maf did have power, and seemed to function normally. I drove it around a little bit and it drove perfectly. The Maf and o2 sensors all sent signals.
The CEL came on, but this time only one code. P0102 (low voltage input to Maf).
I checked the voltage at the Maf, and it was indeed low at 11.7 volts when the truck was running. However my battery volts increased to 14-14.2 volts with the efi2 fuse removed. I normally would read 13.6 to 13.8, had never seen over 14 before.

So... I'm fairly confident that there is a short somewhere on the efi2 circuit. If I can find that junction box #47 it would probably make it easier to find out where. I ran out of light and time today, but will pick back up as soon as possible.

Thank you guys again for your info and help. I will post an update when I am able to do some more testing.

 

Update issue solved...sort of. Since my jumper wire method ran the truck fine, with only one CEL code (low voltage Maf), I decided to just take a shortcut, and run new power to the Maf and separately to the rest of the circuit.

I added 2 relays and fuses (in-line). I ran the trigger wire for the relays to the efi2 fuse, but only on the power side. It took a little modification of a blade connector, and it's a little sketchy, but it fits securely in the fuse slot. I almost just did an "add a fuse" and ran it to another circuit that turns on with ignition, but worried some circuits cut out with the starter, so I might change it up later, but for now this works.

With a separate power wire for the Maf, the CEL went off and has not come back on yet. We will see if the rest of the sensors can survive for a while on slightly lower voltage I guess.

For now it feels good having the truck start and drive normally, without having to connect/disconnect a jumper wire.