Low voltage on MREL pin of ecu

[suprra_girl]

Hey

I seem to have a problem with low voltage on the mrel pin of the ecu. I've tried another ecu with no change at all.
I've checked the various grounds and ignition sources and they appear fine yet my mrel... sucks heh.
I really can't think of how this can happen so I'm going to bypass it till I figure it out.
I'll be adding a new ignition source to the mrel wire and cutting it from the ecu with a fuse and switch so it will act as a killswitch at the same time.

The only reason I happened to find this issue is because I have my wideband hooked up to the mrel ign source via a relay and noticed it had trouble displaying the screen on cranking.

I figured this was the best place to ask as I have no idea how to chase it in the ecu or... somewhere heh.

Appreciate any help

 

[3p141592654]

My recollection is that MREL is directly connected to IGSW inside the ECU. So your problem is most likely with the IG2 circuit from the ignition switch through the IGN fuse and then to the IGSW input on the ECU. Most likely problem area I would think is the ignition switch itself.

 

[suprra_girl]

Thank you 3p I will check it out, appreciate it

Oh and I did mention in the first post that I checked all the 12v sources and they were fine... except mrel. By fine I mean I checked the voltages against the others and they were all holding similar voltage, what doesn't is mrel. (grounds are sweet too)

I ended up bypassing the mrel wire and wiring it direct to ign, funnily enough on the wire you specified. Since doing this voltage has improved dramatically but it's just not enough for me, I prefer it to be working how it should haha.

So I guess we can eliminate IG2 as a suspect. I'm guessing the problem is inside the ecu somewhere :/
Also I've been doing a bit of research and found that the mrel wire reserves power from the ecu to reset the isc back for the next cold start. So I may run that directly back to the ecu mrel wire but I'll find out if I have horrible starts first heh.

 

[3p141592654]

It is okay to jump IGSW to MREL externally. It is already jumpered internally so won't do any harm. AVoid connecting anything else other than IGSW to MREL though, as the micro in the ECU can route power from BAT to MREL as needed to reset the ISC, and if you are not careful with what you connect to MREL it may try to power up the entire car, which will fry internal components.

 

[suprra_girl]

I think I'll leave the new ign source on the mrel wire but I'll find that wire on the isc and wire that directly to mrel.
At the moment I've done this

Original
MREL at ecu ------- Fusebox

Now
MREL at ecu ------- | Cut off

Fused & switched
IG1 -------- Fusebox


Oooh, I lied, I'm using IG1 not IG2

I have a few things running off IG2 tho, my prosport gauges x3, turbo timer probly something else.
The mrel wire wouldn't be getting annoyed by me having a relay on that circuit to power my wideband would it?
I'm using mrel as the ign source to switch it on (screen).
I need to look at the wiring but wouldn't that also suggest that the wideband heater is being turned on via mrel as well, would that cause my problem?
Should I find a different ign source for it?
I'll find the isc wire and put that back on the ecu mrel wire so that it works properly

Hope my stupid diagram helps you figure out what I've done lol

 

[3p141592654]

I would not load either the IG2 or MREL lines at all. Both are mission critical and connected to sensitive circuits in the ECU. I would also stay away from the B+ circuit as well due its its mission critical role.

Use the GAUGE cct for any extra instrumentation that needs to be controlled by the IGN switch. That is how Toyota designed it.

 

[suprra_girl]

Awesome, cheers 3p