2003 Tundra 4.7 L truck Mrel high side

For all of you folks, I am wondering if any of you has experienced an issue with the EF1 relay energized due to MREL line reading high off ECU when the Ignition switch is off creating a problem of draining a fully charged battery in 6-8 hours (discharge current =2.46A). The EF1 relay is good and is normally open as it should be.
Notwithstanding this slight issue, the truck runs as good as it did in 2003 (bought it new). I have no reason to suspect anything else, but thought I ask in case someone had this issue caused by an ECU.
Secondly, how do you remove the heater to register duct that seems to be in front of the ECU mount?
much appreciated ,If there is a video or article you can share.

Thanks,

Alex

 

As this is the first time posting here....Welcome.

Given 1st Gens are different from each other when it comes to electrical or mechanical issues, knowing what engine type(2UZ or 5VZ), cab type(RC,AC) really helps when needing assistance.

Very carefully....
Actually the vent tube should unsnap if you somewhat push the 3'' vent pipe to the left and remove it.

As for the MREL(Main RELay) output from the ECM, it should only have 12vdc when key is in IGN ON position.

IGN ON sends 12vdc to IGSW input to ECM and the MREL control circuit then sends 12vdc out the MREL output of ECM to energize the EFI relay.

You'll need to chase wires to determine why 12vdc is at the IGSW input to ECM.

Contained in the below sticky thread is a link to EWD(electrical wiring diagrams) that should help. If reading EWD's is not your cup of tea, let us know engine size and cab type. We can then help further if need be.

So ... you wanna buy / just bought a 1st Gen Tundra, eh? | Toyota Tundra Forum

 

Thank you BubbaW for your rapid response.
Indeed, The Gen 1 Tundra is a 2UZ_FE with AC cab.
Removing fuses to bypass 12V into ECM does not remove MREL being high. The attached shows my conclusion based on what the wiring shows. Question is ECM module has a voltage leakage between Batt and Mrel pins @ A#3 to A#8 per attached ECM connection.
What do you think?

Alex

 

Very plausible given we have seen numerous times over time and especially these last couple of weeks with rain all around the country, water penetration into the cab has been a culprit.

My suggestion is to check very closely at the connections that are behind the driver kick panel. I would concentrate on the 26 pin connector IA4.

If need be, you can also unplug IA4 and check for 12vdc at pin 15(black/yellow), both directions, which shouldn't be there with key out of ignition
.
Keep in mind pin 6(black/red) of connector IA4 has 12vdc at all times to keep ECM volatile memory alive and well via the BATT signal at ECM pin 3.

 

And to @BubbaW's point, the damage may not be blatantly obvious, here's one of the last cases he helped another member solve recently: https://www.tundras.com/threads/electrical-problems.156818/#post-3895429

Note how, if the connector was closed, or the OP hadn't inspected the wires carefully, he'd have never found it.

 

Thanks Buddy.
Ok with Water getting in. TO be clear, Wouldn't water dry out assuming it shorted out say two pins?

Are the connectors labeled?
Also is the IA4 connector inside the vehicle per picture sent behind the steering wheel inside the vehicle?
From the picture, it seems like it is in the engine compartment area.
If I disconnect 1A4 connector, Pin 8 on the male side connected to ECM, you would expect MREL to be low with IGN switch off, but the female side would be high. Is this what you think?
Alex

 

Connectors are not labeled but IA4 will be the only fairly large 26 pin connector.

As I mentioned above, IA4 and the others aligned there with IA4 I highlighted, are behind the drivers kick panel. That panel is to the left of your parking brake with a black plastic nut holding it in place.

I don't recall the orientation regarding male/female of IA4. What I will say is that it should be obvious which side the connector/harness is going thru the firewall and the other end goes to ECM.

If and when you take a look at IA4, you either have an AHA moment or you will see which way you have 12vdc, either toward Engine Bay or toward the ECM.

I would even consider if/when you have IA4 unplugged, to unplug E3 of the ECU also, if you still have it open and perform a continuity test of pin 8(black/yellow) to pin 3(black/red) that's going toward ECU, they should not show a short to each other.

With IA4 still unplugged, if you wish to check the other direction for those 2 conductors shorted to each other, unplug EFI relay AND 15A EFI fuse....pin 8 and pin 3 should not show a short to each other in that direction.

 

Gents, I have attached pictures showing dubious activity taking place in the ECU, in the same corner where the MREL and Batt connector plugs in. There is no marking which connector is which. so I relied on ohming out the EFI1 relay solenoid coil pin connected to MREL which read 10kohm to gnd in both directions and removing ECU connectors until the ohmeter read open. I was surprised when I opened the ECU and saw this Goo in the corner where MREL is connected to. what really surprised me is the truck ran like a hummingbird and there is no trace of water leaking anywhere around the connectors that I could see. The truth be, I was not looking forwar to removing the Kick panel, Thanks to BubbaW I learned something today.
Now, the other side where the Microcontrollers and PCM memory chips are looks as good as new. So I am wondering if cleaning the Goo which I do not know what it is, all the electrolytic caps are on the very clean side, so I know it is not electrolyte.
What do y'all think I should do next?
I am betting this caused my problem but have no clue what the root cause of the goo is. Components looked intact

Alex

 

I can tell you exactly what it is, because we've seen it before. It's linked up in the community infodump megathread, note bolded text in the subject bullet point from that thread, and be sure to click the "(pics)" link for a very eery echo of your pictures above:

• 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), correct routing info here. 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.

 

Oh, and the resolution you need:

Look at the cover of your ECU. Get the 10-digit hyphenated number off the cover XXXXX-XXXXX. Find a used ECU with the same number (note: others may be compatible; part numbers changed; if you give me the part number I can run it thru Toyota's Parts system and give you some compatible part numbers)

Poorly sealed (or cracked) windshields (and one specific cowl fastener) are known to carry water down along wiring bundles and into the ECU to cause this.

 

For future reference, starting from right side, E3 is first connector then 4, 5, 6, 7.

The below is from the 2003 FSM that one can download from this link....

So ... you wanna buy / just bought a 1st Gen Tundra, eh? | Toyota Tundra Forum

Unfortunately we see it too often which is why we have this sticky thread....

Definitive 2000-2006 cab-area rain water leak thread | Toyota Tundra Forum

Way less complicated than getting to the ECM by long shot

 

You’re lucky. The board appears to be conformally coated for protection.

 

AFter gently Cleaning the board and all with Contact cleaner, Installing it back, it seems that MREL is not high anymore! That said, The truck is not kicking the starter on and truck is now not useable.
My only play is to replace the ECU with a similar one.
Any recommendations? I see some on Ebay with same P/N but don't know if this is the way to go. I do know you cannot get a brand new one from dealer.
Does anyone have a schematic of the ECU board?
BTW, you gents are great human beings, I never anticipated the sheer support from y'all

Sincerely,

Alex

 

If you mean an actual schematic showing all the solid state components and what not, good luck with that. However, if you do find one, Please let us know. Seems Toyota makes that somewhat proprietary

If you feel you've exhausted all checks concerning your present problem and feel confident the ECU is issue, Flagship One is who I personally be using.

2003 Toyota Tundra 4.7L - ECM ECU PCM | 89661-0C442 | Flagship One

 

FS1 as Bubba mentions is great. But we did have one member here recently that got a super sketchy, spraypainted ECU from them that looked janky as hell (guess they were low on stock) so I'd be remiss if I didn't report that.

Note that Toyota applies "-84" to the end of part numbers that have been refurbished by them/their partners. So while your ECU is 89661-0C442, they may have a refurb under the part number 89661-0C442-84. Toyota doesn't have it available for sale (disco'd/NLA), but I did find another site claiming 89661-0C440 to be a possible alternate part number, therefore going by Toyota part numbering logic, 89661-0C441 may also be.

eBay is fine on used parts, as long as the seller (A) has 98%+ feedback on a couple hundred sales and (B) accepts returns, in the event you open it up and it's damaged also. You'll pay half as much.

Avoid buying from Toyota Parts Deal.

 

Barely made the mark

 

I looked for a schematic but cannot find one. I am curious how Flagship one and ECUteam.com are able to repair.
I just can't give it up yet. The low current startup relay has one side of the solenoid connected to gnd and the other side coming from ECU. However it is not straight forward I can't get the solenoid high side terminal to go high. I will not know unless I can see the internal schematic.
Alex

 

I would also remove the plastic cowl cover and get some new little inserts and seal them well to prevent further water intrusion

 

FS1 takes viable units and refurbishes, then re-flashes the ECU with most recent firmware, cleans up the chassis, then resells. They average about $200-280/unit on our trucks for that.

if that’s what was inside your ECU, I suspect some of your wiring could be bad. Clearly the ECU is fucked and should be replaced before continuing troubleshooting. You should review the connectors that plug into the ECU as well for pin corrosion - you had to have contaminants (likely water) enter from somewhere. The corrosion I’m seeing on that PCB looks like it originate with water, or would be what you see from cap leakage, but there’s no caps on the PCB in this case….

 

The wiring and ECU connectors look new upon inspection. The ecu box cover mounts at the bottom; I am not sure how water would roll up against gravity and squeeze into box. The discoloration I saw appears to be heated conformal coating over the last 22 years. The electrolytic caps are on the other side of the board which looks new and shiny with conformal coating.

What perplexes me is that truck ran well and all functions worked except for MREL line always high causing the root problem I had which was draining the battery. After cleaning and reinstalling the ECU, the starter relay does not get energized and truck does not start. I re seated the ECU connectors a second time with same result.
My next action is to replace the ECU.

 

Finally replaced the ECU I got from Ebay and that seems to get the truck running again. I want to thank all of you for your great feedback and support. I could not have done it without y'all.
God Bless you all