2zr MAF amperage draw, help needed

[tmontague]

I'm trying to tackle a parasitic draw problem I've been having for the past few months and while I was testing it out today I have found out that my MAF sensor while plugged in, draws about 90mA of current (0.09A).

Can anyone else with a 2zr swapped Yaris please do me a huge favor and test their parasitic draw with their MAF connected and again with the MAF connector unplugged at the sensor. Just make sure you wait 30 seconds before you confirm the reading as the ecu will wake up and then sleep after 30 seconds when you disconnect and reconnect the probes on the battery.

To do this just disconnect your negative terminal wire. Place one lead from your multimeter on the negative terminal and the other on the negative terminal clamp which you removed. Set your meter to read Amps and you are good to go.

Thanks a lot for whoever can get me this info.

[atomic_hoji]

Awesome find Trevor - I mean awesome as in well done, because the problem is really a pain in the ass and not awesome.. :biggrin:

I had a suspicion the same suspicions you describe re: a parasitic draw in the Fall after letting the car sit for a few days, then with the wicked cold lately I ran into the same problems: 2 days and she needs a boost. I actually keep a charged truck battery in my back-seat so I can get home from work; just in case. Just haven't had time to look into it with exam this past Friday, then low an behold you brought it up. :thumbsup:

I just did a quick check, and sure enough, with the MAF plugged in I get about 250-300mA, bouncing around some, then after 60s it drops to about 185mA. If I disconnect the MAF and do the same test, it's immediately lower, about 150-180mA and after 60s drops to about 100mA. Definitely seems to be contributing to the problem for me, and would explain your 90mA draw pretty well.

Trick now is to find the solution - without unplugging the MAF every evening.. lol

-- Adam

[tmontague]

Awesome find Trevor - I mean awesome as in well done, because the problem is really a pain in the ass and not awesome.. :biggrin:

I had a suspicion the same suspicions you describe re: a parasitic draw in the Fall after letting the car sit for a few days, then with the wicked cold lately I ran into the same problems: 2 days and she needs a boost. I actually keep a charged truck battery in my back-seat so I can get home from work; just in case. Just haven't had time to look into it with exam this past Friday, then low an behold you brought it up. :thumbsup:

I just did a quick check, and sure enough, with the MAF plugged in I get about 250-300mA, bouncing around some, then after 60s it drops to about 185mA. If I disconnect the MAF and do the same test, it's immediately lower, about 150-180mA and after 60s drops to about 100mA. Definitely seems to be contributing to the problem for me, and would explain your 90mA draw pretty well.

Trick now is to find the solution - without unplugging the MAF every evening.. lol

-- Adam

thanks a ton Adam for replying to this thread and checking your MAF draw, you saved me a $100 purchase off of RockAuto for a Denso MAF. Really interesting to hear you have essentially the same issue - I'm assuming you wired your MAF power to the LH light bulb fuse like we all did?

I would love to hear about others with their 2zr swaps and what their amp draw is with their MAF disconnected and connected. I have a feeling that the LH light bulb is not ignition switched like the power source the MAF needs. The headlights don't need the ignition on to work as long as you switch them on. I never actually tested that fuse to see if it was ignition switched as I just tapped into it based off of previous swap instructions.

I tested my 1zz MAF on my Vibe and sure enough, there is no effect on the amp draw with the MAF disconnected and it would make sense that the MAF needs no power while the car is off.

I had a few electrical issues which is why it has taken me a while to get down to the bottom of this and likely why this has never caused me a problem when I first did my swap. I had a low charging alternator (11-12.4V) which CT originally said was a bad battery. I only started to test the alternator and monitor my voltage gauge when I had the same issue with the new battery. New alternator solved that issue.

I also found out last night that I had an issue with my keyless entry where it would randomly trigger the internal relay in its computer and sometimes even turn the dome light on in the middle of driving. This started late last year. I didn't know until last night during testing that is was actually keeping the ECU-B circuit from going to sleep therefore drawing an extra 110mA consistently overnight.

From my testing last night I found the following for a 2zr swapped yaris:

-Normal parasitic draw (No MAF, and ECU asleep): 30-40mA
-ECU asleep with MAF wired up: 120mA
-MAF wired up and bad keyless entry causing ECU to be awake: 260mA-320mA

Base amperage draw from each device:

-ECU asleep: 10-20mA
-ECU awake: 120-130mA
-MAF: 80-90mA
-keyless entry 20mA

With the above info there is about 20mA of "unaccounted for" amp draw, this makes sense and would cover the clock as well as the light for the immobilizer. 30-40mA is a value that is very acceptable and would not cause my battery to die for a few weeks in the dead of winter and likely 2 months in the summer.

The issue I'm having is the extra 90mA from the MAF, plus the 120mA from the ECU that was caused by the faulty keyless entry module. This extra 210mA of draw is enough to cause a no start in 2 days and even over night in -25C weather.

I replaced the keyless entry with a new module I had lying around. If this one doesn't start randomly clicking on me then it should have fixed the issue. I tested it and it worked properly and allowed the ecu to go to sleep.

I am now down to about 130-140mA total draw with the MAF connected. This is much better but it is still too high and something that should be addressed with the cold we get here.

My next step is to test the fuse that the MAF wire is tapped into with the fuse tap. I am going to try and use another proper ignition switched source and see if that addresses the problem. This would also be why the warm weather 2zr swap guys have never had an issue. A 130-140mA parasitic draw is not enough to kill a battery in warm weather starting unless it sits for well over a week

[06YarisRS]

EDIT: I was typing this while you posted, Trevor... And, to second Adam on the "great find", you may have just saved me buying (and eventually ruining) a new battery!

My results:

MAF plugged in -.22
MAF unplugged -.14

So, it looks like I too have parasitic draw in the order of 80 milliamps from the MAF sensor alone. :frown:

Even with the MAF disconnected, 140 mA seems high. I do have that Android headunit in there that might be drawing some power, I suppose. I've been keeping my battery on a tender while in storage, but before I did, my battery was discharged enough after several days to require a boost. I attributed it to a bad battery.

Hopefully a solution to this problem can be found.

EDIT: The location into which I plugged my mini-add-a-circuit is the "LH lightbulb" location? I should go out and test to see if that location (the same as yours Trevor) is switched. Until this is sorted out, I suppose I should disconnect my MAF as I'm guessing it's probably not good for it to be constantly powered?

[atomic_hoji]

No problem! Glad it saved you the order from RA. :thumbup:

I did not actually tap off the LH lightbulb - I don't even recall that from the other swaps to be honest.. lol. I originally had the MAF on a 12V supply in the CA3 connector (26-pin connector into the main junction box from the engine harness). When I suspected that was causing problems, I cut the wire and ran a fuse tap in the main junction box off a random location where the tap fit and I could put the lid back on. To be honest, I didn't think about whether or not the line was ignition or permanent power. Tomorrow I'll take a poke around and confirm if it's a permanent power (must be..) and check some other locations as well. Because it's in the main junction box I'll have to check in the wiring diagrams to see if I can confirm by drawing what bus (supply) I'm tapped into.

My parasitic draw is notable even with the MAF disconnected as well. I know I have the Valvematic line direct off battery, which is what my suspicion was - even though without the ECM live I didn't expect it to be operating, I've been wondering something is staying energized... Again, need to check wiring diagrams to confirm.

Ha.. it's funny you mention clock, etc.. I was wondering why my multi-meter was showing a 'bounce' in mA reading, when I check tomorrow I'll have to pay attention, but I wonder what the current draw is for the alarm light? lol - a stupid blinking light on the dash causing confusion.. Have to check with and without the car locked and alarm set.

Never-the-less, I'll check back with what I find but also interested to hear what others have found in addition to yourself and Adam...

-- Adam

[tmontague]

Yes, until I have a chance to test the LH lightbulb fuse simply disconnecting the maf at the sensor connector will remove 80-90mA of draw. MAF's typically have a heater in always thought, so running constant power to them could cause a constant draw. Either that or they are always measuring intake temps as that is where the IAT reading comes from

Your 140mA that you had left over is the exact number I had when the ecu was still awake. Make sure you keep your probes on the baggery/terminal for over a minute. You should see the amperage drop to below 40mA at one point. If that doesnt happen after a few minutes then either the ecu is staying awake from something or something entirely different is pulling that draw.

Easy way to tell is to pull fuse "ecu-B" and then re test amperage draw with and without maf connected and see what you have.

Take note*** simply disconnecting your probes from the terminal and/or clamp will re awake the ecu as it essentially disconnects and then reconnects the battery. So will opening or closing doors or locking and unlocking them. That amperage long enough for the ecu to sleep (approx 1min) so you get proper amp draw

[06YarisRS]

Yes, until I have a chance to test the LH lightbulb fuse simply disconnecting the maf at the sensor connector will remove 80-90mA of draw.

Your 140mA that you had left over is the exact number I had when the ecu was still awake. Make sure you keep your probes on the baggery/terminal for over a minute. You should see the amperage drop to below 40mA at one point. If that doesnt happen after a few minutes then either the ecu is staying awake from something or something entirely different is pulling that draw.

Easy way to tell is to pull fuse "ecu-B" and then re test amperage draw with and without maf connected and see what you have.

Take note*** simply disconnecting your probes from the terminal and/or clamp will re awake the ecu as it essentially disconnects and then reconnects the battery. So will opening or closing doors or locking and unlocking them. That amperage long enough for the ecu to sleep (approx 1min) so you get proper amp draw

Thanks. I may not have left the leads on long enough. I was pretty sure it was well over 30 seconds, but my hands were starting to freeze. LOL. I'll repeat the test tomorrow and post up my numbers.

[tmontague]

Solution found! Took 5 mins to fix it this morning when I hooked my battery back up after charging. I'll post the solution and pictures later today when I get a chance, but long story short, the headlamp fuses are constant 12v, not ignition 12v like the MAF should have.

I am now down to 20mA of parasitic draw which is well within the normal and should leave your battery fresh (assuming it's a good battery)

[06YarisRS]

Solution found! Took 5 mins to fix it this morning when I hooked my battery back up after charging. I'll post the solution and pictures later today when I get a chance, but long story short, the headlamp fuses are constant 12v, not ignition 12v like the MAF should have.

I am now down to 20mA of parasitic draw which is well within the normal and should leave your battery fresh (assuming it's a good battery)

Fantabulous! Awaiting the fix. The fuse tap just moved to a new location in the fusebox?

[tmontague]

Fantabulous! Awaiting the fix. The fuse tap just moved to a new location in the fusebox?

Yes to the EFI fuse, it is one of the only ignition switches 12v sources. I moved some connectors around to make it easier to run the fuse tap wire

[myfirstyota]

Yes to the EFI fuse, it is one of the only ignition switches 12v sources. I moved some connectors around to make it easier to run the fuse tap wire

I guess I may have to take a look at mine now. I just populated an empty fuse slot with the proper connector. But with all busses being powered all the time, i can inly imagine ill also have an issue but have yet to see it. Im Also not driving the car so no reason why i would have seen it yet.

[tmontague]

I guess I may have to take a look at mine now. I just populated an empty fuse slot with the proper connector. But with all busses being powered all the time, i can inly imagine ill also have an issue but have yet to see it. Im Also not driving the car so no reason why i would have seen it yet.

Yup, I tested all the empty and other used fuses and they were all constant power. The last one I tested was the EFI fuse and it was ignition only based on my testing and confirmation.

Keep in mind your draw will only be 110-140 mA, not 300mA like mine was since you dont have a faulty keyless entry. Still enough to slowly drain a battery but not as quickly.

Either way, having constant power to the MAF can't be helping its longevity with its temp sensor

[06YarisRS]

Yes to the EFI fuse, it is one of the only ignition switches 12v sources. I moved some connectors around to make it easier to run the fuse tap wire

Awesome. Thanks. Don't have the fusebox diagram in front of me now. Hopefully my wire is long enough to reach. Were you planning a pic? :biggrin:

[tmontague]

Awesome. Thanks. Don't have the fusebox diagram in front of me now. Hopefully my wire is long enough to reach. Were you planning a pic? :biggrin:

Yes, once I'm on my laptop in an hour I'll post my imgur pics up. You current set up will be long enough as the fuse is actually a bit closer to the wiring loom than the lightbulb fuse

[06YarisRS]

Supah! Will make the change tomorrow and take new readings after waiting at least a minute. Kid hockey tonight.

[myfirstyota]

Either way, having constant power to the MAF can't be helping its longevity with its temp sensor

I was thinking that when I did the swap. "Its ok to have the maf powered all the time?" I came to the conclusion everything else on the buss was.... must be fine.

[tmontague]

Here is the quick way to fix the MAF power source problem without having to really change any of your wiring from when you did the swap.

https://i.imgur.com/WZms2zv.jpg?1

The pic above I am pointing to the fuse you want to use (EFI 2). This is where you add your fuse tap to. You can see the two white connector wires sort of run in the way. I unplugged them and crossed the wires the opposite way so it leaves a channel to run your fuse tap wire through. This is seen in the image below.

https://i.imgur.com/smLBa4b.jpg?1

This above image shows the fuse tap in the new location and the old LH headlamp fuses back to normal with their 10A fuses in place. My probe is placed on the wire I moved out of the way for the fuse tape wire

https://i.imgur.com/OtjJOkG.jpg?1

This image shows the exact location of the EFI 2 fuse that you want to use as it is ignition switched.

Now that I have a fully charged battery that isn't draining, my engine spun over quicker this morning than I have ever heard it before. Oddly enough on my morning drive I heard my keyless entry relay click twice and the second time it actually locked the doors by itself. If this happens again I am going to scrap the whole keyless entry completely. I haven't confirmed that the new one is causing the ecu to stay awake, but it shouldn't be auto locking like it is.

[06YarisRS]

Kudos, Trevor! We should all take your new found info and update our swap threads.

[myfirstyota]

Ok so i really dont like the fuse tap idea. Not because theres anything wrong with it, i jist wanted a clean fusebox.

Would it be a good idea to splice into the output side of the efi fuse inside the fusebox and possibly install a slightly larger fuse into the efi spot?

[tmontague]

In the chance of an electrical issue pulling more current then the EFI system should your protection on the system is gone. Its rated for 10A if you splice down stream and increase the amperage of the fuse, then you could potentially over power the EFI circuit.

You could try keeping the fuse at 10A and see if it blows. I cant remember exactly how the fuse taps are wired internally but it does use the original fuse/circuit to power the added circuit and it never blows the original 10A circuit. But it also may be internally wires separately.

You likely will be fine but IMO the fuse tap is well worth no extra loaded circuits. Once the fuse cover is on, it is as clean as factory spec. Plus if you ever needed to remove the wire it's as simple as disconnecting it which I always like

[06YarisRS]

Swap to EFI location complete.

New reading with MAF plugged in and after the ECU goes to sleep (about a minute):

30mA

Battery is reading 12.62V now and I decided to remove the tender. I'll let it sit for a few days, go back out and check voltage.

Once again, Trevor, thanks for this!

[myfirstyota]

In the chance of an electrical issue pulling more current then the EFI system should your protection on the system is gone. Its rated for 10A if you splice down stream and increase the amperage of the fuse, then you could potentially over power the EFI circuit.

You could try keeping the fuse at 10A and see if it blows. I cant remember exactly how the fuse taps are wired internally but it does use the original fuse/circuit to power the added circuit and it never blows the original 10A circuit. But it also may be internally wires separately.

You likely will be fine but IMO the fuse tap is well worth no extra loaded circuits. Once the fuse cover is on, it is as clean as factory spec. Plus if you ever needed to remove the wire it's as simple as disconnecting it which I always like

Ok so my next question is:
For the efi fuse.. is it powered by a buss like the others?
Or is there wire feeding the powered side of the fuse? If there's a wire feeding the fuse, I could splice off that wire and run to an empty fuse slot, no?

[tmontague]

Swap to EFI location complete.

New reading with MAF plugged in and after the ECU goes to sleep (about a minute):

30mA

Battery is reading 12.62V now and I decided to remove the tender. I'll let it sit for a few days, go back out and check voltage.

Once again, Trevor, thanks for this!


No problem, glad to help and hopefully it saves someone from being stranded with a dead battery. 30mA is a fine parasitic draw and will not kill your battery for a long time


Ok so my next question is:
For the efi fuse.. is it powered by a buss like the others?
Or is there wire feeding the powered side of the fuse? If there's a wire feeding the fuse, I could splice off that wire and run to an empty fuse slot, no?

I don't know for sure but I don't think its powered by a bus as it sort of fits by itself and it is one of the few if it only fuse in the fuse box that is ignition controlled.

There is a bank of fuses on the right of the fuse box that are all constant power and I'm pretty sure those are bus supplied.

You could probably lift the fuse box and chase a wire to the EFI fuse to see if there is a wire supplying it to tap off of. Too much work for me though, a fuse tap works perfectly and is quick

[myfirstyota]

Yea if it wasn't winter is have just cracked open the fusebox and looked but cause it's cold, just wanted to see if anyone knew off the top of their head

[tmontague]

Yea if it wasn't winter is have just cracked open the fusebox and looked but cause it's cold, just wanted to see if anyone knew off the top of their head

You mean you don't like wrenching in pouring freezing rain?!:biggrin:

[myfirstyota]

While standing in 7" of wet slush? Naa not a fan lol

[atomic_hoji]

You mean you don't like wrenching in pouring freezing rain?!:biggrin:

^ this. Then 80-90 kph winds later in the week kept me from bothering with it.. ambition lost to necessity. lol

Just a confirmation for the 3rd gen. I did drag my butt outside and check today, and basically any of the open spots in the main junction box are 12V constant supply, unless you move onto the ... "cartridge thingy" (?!)... that has the EFI fuses and IGN fuses. Some (not all) of those are ignition supplied, so I moved the MAF fuse tap onto one of those, then re-checked. Noticed that the shutdown current was bouncing a bit, but down to 150-180mA or so, then after 60s dropped to about 100mA. Looking back now, this jives with what I found with the MAF disconnected.

I did try removing my battery supplied constant power to the Valvematic to see if it would further reduce it, and found that it made no difference. I imagined that it would have been keeping something energized, but I guess until requested to change position, the Valvematic draws nothing for current.

Regarding using a fuse tap vs. wiring - I don't recall if I posted the picture, but pry open and look at the back-side of the main junction box - it's a rats nest of epic proportions in there! And to power a slot you need the correct terminal to clip into the junction box as well - the fuse slots are not the same as regular connector terminals so far as I can tell. I thought about it, then decided to use the fuse tap to "make it work first, then tidy later" and to be honest the fuse tap is working just fine.

Also, just to clarify, fuse taps wire in parallel. The circuit you tap remains one branch, and the new tap parallels a new branch off the supply side of the original circuit. There is no change to the downstream (device) side of the circuit you tapped off of as it remains fused with it original fuse and downstream there are no changes. The upstream wiring and any upstream fuse will now have to handle whatever load you have tapped onto the circuit though. In our case, if the upstream side is powered off the 20A Main EFI circuit, the MAF is now added it's current load to the circuit wiring you tapped and the Main EFI fuse; which I believe the MAF is downstream of the Main EFI fuse anyway in factory setup. The only risk is to the supply wire of the circuit you tapped.

I'll have to have another look as to why my 'base' draw is still around 100mA when I get an opportunity - maybe March break if the weather is nice.. get the car washed, badged, and tidy some little bits. Meantime, thanks again Trevor for raising the issue and chasing it down! :thumbsup:

-- Adam

[tmontague]

Good info on the fuse tap. I always thought they were wired parallel but I remember not having power to my additional wire when the fuse from the original line was removed from the tap.

Your 100mA parasitic draw seems a bit high. It probably will keep your battery fine for at least 5-7 days in the dead of winter and much longer in the summer, but it should definitely be below 50mA, something else is drawing current.

Start with any aftermarket/2zr swap wiring, and then pull factory fuses and see what drops the draw.