How to replace the "Main Body ECU Compu Network"

[rigtec]

G'day Tech-team!

I thought this was an Important subject to approach (not too much on you-tube on the subject)! I did mine TWICE this week, ugh! I had never seen one done so this was a learning experience for me! My MB-ECU acted up about five years ago (ALL warning icons were on, on the Instrument Cluster, and no communication from the OBD-II). When it happened, the truck was still under warranty, so I took it in. The dealership gave me a hassle because of a few electrical mods that I'd installed e.g., PIAA fogs, AOB switch, sub-woofer amps and power lines (w/in-line fuses) running to the battery...etc!

So they told me to remove all aftermarket systems, 'BEFORE' they would trouble-shoot the trouble I was having! I told them a few things in my particular street-Background style language; which I don't think they understood, but they all got the idea that I meant business, and they ALL REFUSED to come outside with me! The local mechanic shops weren't able to work on it at the time because they weren't familiar with Toyota's ecu software/firmware, nor did they have the OBD-II Techstream analyser for the truck! So, being on my own, I ordered a NEW Main body ECU Compu. As luck would have it, as soon as I ordered the part ($630 plus bucks), it snowed, dropped about 30 inches, so my plan was done!

Before the snow melted and got warm enough to work in my driveway (several moths later), it started working again, so I never changed the compu-net, I put it on ebay for sale! A few weeks ago it got really cold here in Jersey; about 6 degrees F. That's when the trouble re-appeared, e.g., SRS Airbags, door ajar, steering system, Brakes, ABS, seatbelts, Tach-o-meter and Speed-o-meter quit...etc, ...this truck is running here btw:

I went about the procedure, checking for a power loss at both fuseboxes. I performed a Master RESET, but no dice. After about two weeks, I said fuk-kit', I'm changing the MB-ECU! So I did that, only to find that the trouble remained, so I knew that, that's not the problem.

Today I rechecked ALL of the fuses, and found four fuses without power, both on the line and the load side; two inside and two in the main relay/fusebox in the engine room. Well I learned that the four fuses that were completely dead were the Low beams, the High-beams, the Tail-lights and the 'Back-up lights! I never realized that the lights MUST BE ON for the fuses to be live, so these fuses are AFTER the stalk switch & relay. The stalk controls the relay, and then the relay feeds the lights through the 10A fuse(s)! That's when I chose to put the Original MB-ECU back in the D/S Junction/fusebox!

The first time I did it (on Saturday Mar 16'th), it took about three hours because I wasn't sure about what I'd have to move out of the way. But today it took me about one hour to get it out-&-in, and done! Okay, so here we go! First remove the NEG Battery terminal from the battery, "See below":


Now remove the door-jam and D/S kick panel; I'm sorry I didn't remember to take shots of the removal of the door-jam, kick panel, the lower airbag bolster panel, but I'm sure that there are multiple photos of getting into the lower bolster panel on this forum, my deepest apologies! Once you're in there (it's really no big deal, takes five minutes), I did photograph all else to be done:

The next three photos are the air-bag removal process




Now removing the harness connectors from the Main body ECU Compu



Now I'm releasing the clip that holds the MB-ECU to the fusebox:


The MB-ECU is "Hinged" to the D/S fusebox, just swing them apart once the clip is unsnapped and you're done!




The swap didn't take very long (again, about one hour on my second time doing it) once I knew where all of the retaining screws were (about six bolts and three nuts that holds it all together; all 10mm heads), they're very easy to get to! Now I still need to figure out what's causing the instrument cluster to misbehave... and I'll be sure to let you know once I get it licked! 'Best to you',

rig

 

[lukkystrike1]

G'day Tech-team!

I thought this was an Important subject to approach (not too much on you-tube on the subject)!.........

Just as a quick question, what programming did you do post install? This 'virgin' ECU should need to be registered? or was it Plug and Play?

JW....:smokin:

 

[rigtec]

Just as a quick question, what programming did you do post install? This 'virgin' ECU should need to be registered? or was it Plug and Play?

JW....:smokin:

Hi lukkystrike1,

...No programming necessary; works right out of the box. Now the PCM (Power-train Control Module) is a different story! And thanks for your question!

rig, cheers!

 

[rigtec]

Hey Tech-team,

I tried to make available the procedure of "Airbag Knee bolster panel" removal, and Main body ECU/Driver-side Fusebox Un-hinging, just for those who've never done it; "See photos below":



Main body ECU/Driver-side Fusebox Un-hinged

...I'm still in the process of going through/dismantling my dashboard (daily), and tracing CAN-bus/ECU wiring, while looking for any un-clawed or loose harness connectors throughout the 4Runner's electrical system. I'll be sure to document any problem(s) found and post them! 'Best',

rig

 

[cjimen31]

What led you to pinpoint the body Ecu was causing your issues? It’s very rare that these go bad

 

[flyrv9]

So Rig, do you think there is a connection between the cold temps and this problem?

 

[rigtec]

What led you to pinpoint the body Ecu was causing your issues? It’s very rare that these go bad

...you're absolutely right cjimen31,

But I purchased the New MB-ECU about five years ago (almost $700 bucks), for a very similar problem, but it turned out that I didn't need it. The MB-ECU had lost power so it chose to light-up my instrument panel like a Christmas tree! It started happening again about two weeks ago.

I checked for power at the Short-pin and the B-ECU electrical buss and ALL fuses, and all was good. Well I ran out of random stuff to blame the trouble on, and since I already had a new ecu in the closet, I chose to through it in; but that's not it, so I put the original one back in.

If it were just the ABS or Brake warning lights, I'd have somewhere to start e.g., wheel speed sensors, but it's the SRS, seat-belts, door ajar icon, instrument cluster back lighting, Tach-o-meter and Speed-o-meter completely dropping out, security system, VSC, slippage warning, steering, A-Trac...etc! So it's not any particular system warning to help isolate it!

And again, you're right... I have yet to see a Main body ECU go bad!

rig, cheers!

 

[rigtec]

So Rig, do you think there is a connection between the cold temps and this problem?

Hey flyrv9,

I did seriously consider the ultra low temps in Jersey (6 deg F with the truck just sitting) when the trouble started! But it's been 50 deg f after that, so... :noidea:

tell me(?) :cheers:

 

[flyrv9]

I dunno - cold usually makes electronics work better and faster; but there have been issues related to connections and cold. Depending on the type of connection, a poor connection (loose, bad crimp, poor solder joint, unlocked pin or socket in a connector, etc.) can shrink a little when cold and make a connection fail and open. Then when it warms up - it works again. Problem is locating the problem. The only way I know of is to examine and test every connection involved in the issue. Experience tells me that without finding the cause, the problem is probably going to appear again. Murphy's law or something like that. I hope you can pin this down for sure.

 

[rigtec]

I dunno - cold usually makes electronics work better and faster; but there have been issues related to connections and cold. Depending on the type of connection, a poor connection (loose, bad crimp, poor solder joint, unlocked pin or socket in a connector, etc.) can shrink a little when cold and make a connection fail and open. Then when it warms up - it works again. Problem is locating the problem. The only way I know of is to examine and test every connection involved in the issue. Experience tells me that without finding the cause, the problem is probably going to appear again. Murphy's law or something like that. I hope you can pin this down for sure.

That's just it flyrv9,

the problem has not gone away (yet?)! And what's worse, the OBD-II isn't communicating with my techstream tool; 'tis like flyin' blind! I've been through it before, but it feels like the first time! The "Limited" has 26 ecu's throughout the body ("Trail" has 27), but what would cause a 'Catastrophic chain destruction phenomena' without ANY work being done to the truck...

rig, cheers!

 

[flyrv9]

Just thinking here - can you connect a code reader to the OBDII port and get anything? Is there a way to force the main CPU into limp mode and then read something. Seems like there should be a way to get a memory dump from the ECU's - reading it might be another problem though. I don't think I'd want to shotgun parts at this problem without returning to the basics and checking all power and grounds.

All should be checked with a good meter. Grounds should be very close to a dead short minus the value of your leads if your meter doesn't have a zero function. Voltages should be very close to nominal and rock stable. Checking main power, ground and alternator output under load and frequency too. Something is causing this - and it may be power related - overvoltage or undervoltage or variable unregulated voltage may be the culprit. Sorry, I just don't know enough about these systems to be much help and I'm sure you know all these troubleshooting methods too. My experience with cascade failures usually traced back to the first to fail forcing the others to shut down or go into protect mode. Good luck Rig.

 

[rigtec]

"Just thinking here - can you connect a code reader to the OBDII port and get anything? Is there a way to force the main CPU into limp mode and then read something. Seems like there should be a way to get a memory dump from the ECU's - reading it might be another problem though. I don't think I'd want to shotgun parts at this problem without returning to the basics and checking all power and grounds..."

Absolutely flyrv9,

I've already checked for power (HOT and GND) at the fuseboxes and the OBD-II port! I'm gonna need to research the CANbus protocols, sensor resistances, and proper wiring continuity 'BEFORE' I start shopping for parts; that's not the way I resolve ANY problems!

My electrical library has some specs for trouble-shooting assistance, I'll let you know what/when I find out anything concrete! Thanks for the replies! 'Best to you',

rig

 

[Turfboy]

But I purchased the New MB-ECU about five years ago (almost $700 bucks), for a very similar problem, but it turned out that I didn't need it. The MB-ECU had lost power so it chose to light-up my instrument panel like a Christmas tree! It started happening again about two weeks ago.

I checked for power at the Short-pin and the B-ECU electrical buss and ALL fuses, and all was good. Well I ran out of random stuff to blame the trouble on, and since I already had a new ecu in the closet, I chose to through it in; but that's not it, so I put the original one back in.

If it were just the ABS or Brake warning lights, I'd have somewhere to start e.g., wheel speed sensors, but it's the SRS, seat-belts, door ajar icon, instrument cluster back lighting, Tach-o-meter and Speed-o-meter completely dropping out, security system, VSC, slippage warning, steering, A-Trac...etc! So it's not any particular system warning to help isolate it!

As I understand the above, It appears there is a power LOSS to the subsystem for the SRS, Seat belts, Door Ajar icon, instrument cluster back lighting, tach and speedo.

I do not have a wiring diagram but would look to a commonality in the power supply for the system or a common ground.

Best of luck!

 

[jbtvt]

Interesting problem. Can't really fault the dealer for not wanting to warranty a modified electrical system any more than you could if they didn't want to warranty body sway in a vehicle with modified suspension, IMO. In any case, have you downloaded all the wiring diagrams for your vehicle from https://techinfo.toyota.com? I'd add them to my collection and check them out one of these nights if you wanted to upload to Dropbox or similar.

Looking at the '06 Tacoma diagrams I have, it looks like the ABS and Trac ECUs are a common link between the lights you're seeing, and they both feed into the OBD2 port as well. Even your door ajar light looks to have an alternate ground through the module fed by these ECUs, at least on the Tacomas. (edit:NM, not a ground)

You might be able to pull some codes using a basic OBD reader that doesn't get any input from those pins, maybe the BAFX one on Amazon? Or try pulling all pins from your OBD port except the power, 2 grounds, and CAN hi and lo and see if you get a connection with either reader then. This would allow you to rule out the main ECU and associated systems at least.

 

[rigtec]

"...Looking at the '06 Tacoma diagrams I have, it looks like the ABS and Trac ECUs are a common link between the lights you're seeing, and they both feed into the OBD2 port as well. Even your door ajar light looks to have an alternate ground through the module fed by these ECUs, at least on the Tacomas. (edit:NM, not a ground)..."

Hi jbtvt,

Thanks for your post; that's a great piece of info wrt the ABS and the A-TRAC; which were the first warning icons on the cluster to show up 'outta nowhere' during a severe cold snap. Ambient dropped to 5-6 deg F for about a week-and-a-half while the truck just sat (Not Used)! The others e.g., security, steering, air bags (SRS), Tach-o-meter, Speed-o-meter, and instrument cluster illumination issues seem to come and go!

That said, I'm gonna start to focus on the power supplies (and GNDs) to the ABS, A-TRAC, and the OBD-II; I think you could be onto something there! I also considered, perhaps a bad wheel speed sensor; which I did climb under the truck and inspected the wire harnesses, then un-clipped and re-clipped them to assure a firm connection... this truck has 22,000 miles on it and has never had any part of the front-end or rear suspension modified!

Thanks again, 'Best to you',

rig

 

[jbtvt]

Low miles for a '12. Other thing to consider since you mention the cold several times is the battery. Voltage is lower in cold temps and if the charge gets low enough the battery will freeze at water temps, and they can be permanently damaged. I see in the pic yours is 4 years old and doesn't sound like truck gets that much use, so might want to rule that out first with a voltage check since it's so easy, if you haven't already.

Def invest in the diagrams in the link above also if you haven't, $20 gets you a 2 day membership and you can download all your wiring diagrams, and any other repair files for your truck and any other Toyota/Lexus.

 

[rigtec]

Low miles for a '12. Other thing to consider since you mention the cold several times is the battery. Voltage is lower in cold temps and if the charge gets low enough the battery will freeze at water temps, and they can be permanently damaged. I see in the pic yours is 4 years old and doesn't sound like truck gets that much use, so might want to rule that out first with a voltage check since it's so easy, if you haven't already.

Def invest in the diagrams in the link above also if you haven't, $20 gets you a 2 day membership and you can download all your wiring diagrams, and any other repair files for your truck and any other Toyota/Lexus.

Thanks jbtvt,

I have a 'Full-Set' of wiring diagrams from Mitchell manuals/eautorepair.net which are very accurate... I've been buying them (2011 to 2016) to provide some level of help for our members here on forum. As far as my battery, it's an AGM (No water), but Gel...and about 900 CCA, 120 mins!



"You've been a 'Tremendous' help to me jbtvt; thank you for your time/efforts, 'tis much appreciated!" 'Best to you' and loved ones!

rig

 

[rigtec]

Well Tech-team,

As promised, I came back to fill you in on what I found wrong with my "Prized 4Runner"! It took a while (that's a given), but considering all that needed to be checked e.g., All relative ECU's, junction boxes, wiring throughout the electrical system, clawed harnesses, switches in the upper map-light/moon-roof console; to say nothing of the CAN-bus system...

I think now we know what's been going on (intermittently), as far back as 2012, when I bought the truck! I had "NO IDEA" that my truck would have any reason to misbehave because of this! I learned that it needed a "Zero Point Calibration", YAW rate acceleration sensor calibration, and a DAC (Downhill Assist Control) calibration!

...I thought you only needed that if you perform a substantial lift, get into a wreck, or are doing some 'SERIOUS' off-roading with "aired down tires" or swapping out the "L or UCA's"! I performed all three calibrations today and the (false) warning icons on the instrument cluster went out! ...even the "Speedometer & Tachometer" started working again!

There's a document by one of our knowledgeable members here on forum, whom I've never met or spoken with; he may have moved on! But thank you sooo much [MENTION=51374]iDRiVaT4R[/MENTION] ; you're a great asset wherever you plant yourself; terrific job! Here's that document if any of you need to see it:

Yaw Rate and Acceleration Sensor Zero Point Calibration - Toyota 4Runner Forum - Largest 4Runner Forum

When this first happened, I went to the Toyota dealership where I bought it. The service department told me that my aftermarket lighting and sub-woofer system were causing the trouble... without even looking at it... said I had to remove everything BEFORE they'd bring it in for testing!

If any one of those techs would've had the confidence/courage to do the "Zero point calibration/YAW Rate Accel sensor cal", they would've solved the trouble years ago; and saved me $700.00 bucks buying a new MB-ECU for nothing! Anyway, I'm glad that this mystery is no longer that! 'Best to you',

rig

 

[Humble Leader]

G'day Tech-team!

hey rig - thanks for this write up. I had been having issues with my drivers side touchless entry and thought maybe the BCM was going bad , or the handle itself. so I looked up how to replace both and came to this thread

when the weather is really cold and dry the driver side handle tends to not sense my touch very well, key fob works fine, other door and hatch work fine. car battery and fob battery are both new. the car senses me because the mirror puddle lights go on when I approach the drivers side but when cold the handle doesn't like to sense my touch to lock or unlock the door.

If I heat up my hand with my breath it works so I thought maybe the handle is just going bad or it's just the cold mixed with dry hands. also works if I heat up the interior of the car which probably heats the door and handle indirectly. what's strange though is sometimes if I cycle the vehicle to IGN and then off, I can get the door to respond to my touch to lock one time, sometimes. I have a new handle waiting to install but I would think if I had a BCM problem it would impact the entire keyless entry system rather than one door?

do you know if the door handles sense heat or moisture from the hands? I did the battery disconnect for 15 minutes and it seemed to fix the problem until it got really cold again but could be coincidence. also left the battery out of the fob as well for 15 minutes

 

[rigtec]

hey rig - thanks for this write up. I had been having issues with my drivers side touchless entry and thought maybe the BCM was going bad , or the handle itself. so I looked up how to replace both and came to this thread

when the weather is really cold and dry the driver side handle tends to not sense my touch very well, key fob works fine, other door and hatch work fine. car battery and fob battery are both new. the car senses me because the mirror puddle lights go on when I approach the drivers side but when cold the handle doesn't like to sense my touch to lock or unlock the door.

If I heat up my hand with my breath it works so I thought maybe the handle is just going bad or it's just the cold mixed with dry hands. also works if I heat up the interior of the car which probably heats the door and handle indirectly. what's strange though is sometimes if I cycle the vehicle to IGN and then off, I can get the door to respond to my touch to lock one time, sometimes. I have a new handle waiting to install but I would think if I had a BCM problem it would impact the entire keyless entry system rather than one door?

do you know if the door handles sense heat or moisture from the hands? I did the battery disconnect for 15 minutes and it seemed to fix the problem until it got really cold again but could be coincidence. also left the battery out of the fob as well for 15 minutes

Hey Humble Leader,

The sensor(s) are in the door handle, so I think you're right... everything else works just fine! No need to worry about the Main Body ECU; that just presides over 26-27 other ecu's on the network. I'd just change the handle and hope for the best!!!

Please let me know how you made out when done! Best to you Humble Leader! rig