BSM System Totally Dead - Troubleshooting Woes (2020 Tacoma)

Calling all Tacoma electrical gurus...

I recently bought a 2020 TRD Sport 4x4 and have been having a bear of a time getting the blind spot monitoring system working (I knew it was dead when I bought it, but figured it would be a sensor, switch, or something else relatively easy). Important to note that all other systems on the trunk that runs to the back of the truck (ultrasonic sensors, backup camera, lights, etc. work properly) The system is totally dead, no DTCs in Techstream and nothing happening when the BSM switch in the dash is pressed.

I have a subscription to TIS (2-day) and will reference the procedures I have completed. So far I worked through RM100000000VFV5 which confirms the presence of power at both BSM bumper modules (plus ground works), and RM100000000VFV6 which confirms the BSM cabin switch works and switched power is making it to the LH module. I also have 3 modules I rotated in, so no chance it's the module.

I checked the resistance of the CA2P and CA2N connectors that run between the two bumper modules and read 120Ohms on each module, which is correct, so those wires are good

I noticed I wasn't getting 12V on the yellow BIND wire that starts at the BSM cabin switch and ultimately runs to the LH bumper module and narrowed that down to high resistance between EB5 under the hood and BE1 under the bumper - I wiggled the entire harness and couldn't locate a trouble spot, so I jumped from under the hood (Pin 14 of EB5) back to the harness under the rear bumper (Pin 8 of BE1) but that didn't change anything.

At this point TIS recommends replacing the LH module, but I've already tried 3 and feel confident they are OK (I opened one and confirmed no visible corrosion or damage)

I tried checking the continuity of CA1P and CA1N between the LH module (pins 2 and 7) and EB5 (pins 11 and 22) and got open for both wires, which doesn't seem right. Next, I checked between J20 Junction Connector (pins 1 and 3) and EB5 (pins 11 and 22) and got open on both of the wires again.

My assumption at this point is there is a break in CA1P, CA1N, and BIND somewhere between EB5 and the back of the truck, and at this point the BSM bumper modules are powering up but can't communicate with the truck, which is why Techstream doesn't seem them at all.

Does this all sound correct?

Is there a way to check CAN function at the two EB5 connectors? I'm thinking of using an oscilloscope between the pin and chassis ground and look for voltage/voltage change, but I've never checked CAN communication before and don't want to mess anything up. Assuming the CAN communication is making it to EB5, I'm thinking the easiest thing to do is to run wires between EB5 and BE1 connecting CA1P, CA1N, and BIND wires from the engine bay to the back.

This has been a much more involved process than I was hoping, however, I'm not giving up Please, if you know anyone who has really gotten into the weeds figuring out electrical issues, I would really appreciate your assistance.

 

Just a quick update: I checked continuity of the green OMIL wire that runs from pin 4 of LH BSM module to EB5 and everything was fine.

Next, I checked continuity between the 4 CAN wires that run between EB5 and J20 (near the rear bumper left side, maybe 18in into the frame) and every one was returning open. I was checking pins 1, 11, 12, and 22 of EB5, which should form two closed loops that run to Junction 20, however, no continuity was found. I even checked continuity between every connector in EB5 and a CAN pin in J20 just to make sure it wasn't a case of the wires not matching the wiring diagram and no luck.

Based on what @Bill400 shared in his post on adding a BSM system to his Tacoma, I should have continuity between the CAN wires in EB5 and the J20 connector, so something is very wrong here. Tomorrow I will expose the wires between J20 and the main trunk to see if there is any damage, as it seems way too unlikely that all 4 are open while every other wire (other than BIND) that runs to the back of the truck works properly. Mainly posting to keep myself sane and hopefully help someone else who may have this issue in the future though I appreciate any advice given too

 

Are you able to communicate with the BSM Master and Slave modules with a scan tool?

 

There is a TSB for the symptoms you describe resulting in replacing the rear sub harness. I have it printed at home, I can share later. I have a similar problem two years ago started working intermittently. No warning lights or codes, now it doesn’t work at all

 

Unfortunately neither module shows up when running a health check with Techstream, and requests to pull data from either module fail. According to Techstream, there are no BSM DTCs and it's like the truck doesn't even know the option is installed.

My understanding (hoping someone can confirm) is the J20 Junction Connector has 6 pins; 2 run to the BSM LH "Master" Module and the other 4 pins run to EB5 in two twisted pairs to provide a loop for the CAN network. Later today hopefully I will have time to inspect the first couple feet of the J20 wires to see if there is an obvious break or sign of damage (given none are currently indicating continuity between J20 and EB5)

 

Thanks, I would appreciate that! I wonder if that's related to the BE1 or BE2 connector, which, if corroded, could cause issues with the BSM system - I've heard others call it the N22 connector I believe

 

Your first post quotes a few very long RM numbers none of us are going to have access to, please attach so others can see. I have attached a BSM schematic for "our" commonality. It is very hard to see what is going on without some common reference. As far as I can tell there are no BSM gurus on this site, so sorry for both of us.

My thoughts have been that the BSM was a stand-alone system and did not need the CAN for operation, only for reprogramming/calibration and to report errors to the Combination Meter via the Network Gateway to display to the driver; of course, I could be wrong, and your experiences say they maybe are.

Your theory that the vehicle does not see the modules sounds sound, as when I have unplugged a module such as the DCM, not to be confused with the BSM, the module disappears from Techstream. Plus, Techstream does not bring up an error saying the module is missing only a blank position with a complete "Health Check". It is my belief for Techstream to see the left module it would be necessary to have POWER pin 5 Light Green wire, GROUND pin 10 White with Black tracer wire and the CAN connections present. There should be power to the two BSM modules at all times for Techstream to see them - the dash switch would have no effect upon this.

From the schematic I can see the 8-contact sealed J20 connector for the CAN you have been discussing. Also, on the same CAN wiring there's a 22-contact J2, an unsealed connector, plus a few other connectors, EB3, IA3, then on to N32 the Network Gateway (perhaps this is where you get N22 from?).

I would take the schematic and recheck for voltages at the switch, power and ground to the modules, etc. before proceeding with the CAN troubleshooting.

What are you using to probe the wires with the connectors connected together? IMPORTANT.

You mention 1200 ohms, a CAN bus IIRC is 600 ohms - this makes me believe you have the connectors apart while measuring; correct? Two 1200 resistors in parallel will produce a 600-ohm bus.

I would like to ignore, for the most part, your initial post as I find there are problems with statements, such as the yellow BIND wire going to the Master Left BCM Module - it does not (well not for power but for ground), at least according to my schematic. It would be better checking the grey BSSW wire for power - this is the power lead that turns on BSM. A very important first step! The BIND wire grounds the LED on the power button.

Just to note:
You have already noticed that the two modules are identical, right and left, and that they both have different functions depending upon their location. Master versus Slave, Power-on versus Back-up, etc.. A piece of interesting Deutsch engineering.

NOTE: It appears the schematic file did not download, that is fine as a more recent file is available in post #10.

 

TSB021317 “license plate lamp moisture and or blind spot monitor abnormal operation” published 01MAY17
I had trouble deciphering my vin to know which wpharness to order and I kinda stalled there.

 

Was the truck originally equipped with BSM?

I'm not sure how Toyota does their configuration of modules to tell each one what the truck is equipped with but I would expect other modules on the truck to be setting "lost communication with BSM" codes if it was supposed to be there but wasn't communicating.

There's not alot to check at the BSM modules, Power on Pin 5 (Light Green), Ground on Pin 10 (White/Black), and CAN lines on Pin 2 (Black) (CAN H) & Pin 7 (White) (CAN L).

CAN terminating resistors are 120 ohms, there is typically 2 terminating resistors so checking resistance between the CAN wires at any point on the bus (with the bus powered down/battery disconnected) should read 60 ohms.
So checking between Pin 2 (Black) and Pin 7 (White) at the Left BSM Sensor you should see 60 ohms if the wires are intact.

 

Thanks for the more recent copy of the BSM Schematic - added to my collection. OP needs to look at it as some things have indeed changed. Such as connectors and pin outs. I hope my old one did not misdirect him too much.

Correct in the two 120 ohm resisters as bus terminators; in parallel they are 60 ohms. I misread the OPs "120Ohm" as 1200 ohm - the power of suggestion strikes again.

As far as "lost communication" errors, I would expect that too, but have as previously mentioned the DCM being disconnected without errors? DCM was not an original feature on the 3rd generation, I think/theorize it was not formally brought into the fold. Was the BSM an original feature in 2016? All of its functions are self-contained, buzzer, lights, communications between the two BSM modules - stand alone as I see it. Might be interesting to disconnect the power at the EB3/EB5 connector to see what happens on a working unit.

 

I wish I knew more about how Toyota sets up/configures their CAN systems on the newer trucks, I just don't get to do much diag on Toyota vehicles in general (they just don't come into the shop much). Any other vehicle typically would have a host of com codes in various modules for a module that should be there but isn't communicating.

I know quite a bit about how all the systems work on 2nd gens from reading service info and reverse engineering/testing stuff on mine but the 3rd gens (especially 19+) are alot more complex and I don't have access to any to do any tests on. I try to help when I feel I can but it's not that easy without fully understanding how the systems work.

It also shows some 3rd gens have a Gateway ECU and 3 data busses but it's not really clear on how to determine whether or not a particular truck has one.

 

The OP referenced a Bill400 in his second post. If I have the correct person Bill added BSM to his truck and included a fair amount of CAN files in his thread documentation. I learned a bit from that endeavor. Bill added wiring only, IIRC no module programming at all. I was shocked.

I miss the old Helm/Manufacturer manuals that started out with a “theory of operation” statement. That statement was very important to understanding the system.

 

I’ve been sidelined by work and spending my free time earlier changing power steering and rear differential fluids (which were both overdue when I bought the truck) but I appreciate all of the input on this thread and will have some pictures and measurements for you all tomorrow. For voltage measurements I’ve been using a Fluke DMM I have from work, so I generally trust the results

 

Toyota has very detailed description and operation of systems, some of it is in the FSM but there is a ton of stuff when you go to New Car Features (NCF) on TIS and pick a model year when they added features.

It shows how it works, all the modules involved, etc.

Looks like all trucks with BSM have a Gateway ECU, I suspect if you have a truck that doesn't have the Gateway ECU the BSM wouldn't work if you tried to add it.

 

DMM isn't ideal for checking powers and grounds, I prefer a test light so I know the circuit can carry a load.
https://youtu.be/xazvmJ8_p5Q

 

I have not been into TIS yet, I do not have reliable internet - sketchy cellular only, never more than one bar. I have to Starbucks just to send pictures and download stuff. One of these days.

I will read through your NCF file later - saved it!

May not be a great idea for all measurements. Many of the voltages are strictly levels in this vehicle and were never meant to put out much current. One I can think of off the top of my head is a 5VDC (level, not a supply) off of the DCM or the radio some people thought they would use to power the microphone. It was just a signal level supply to tell some device that was activated. Also, lots of the switches are voltage divider resistors who can take no power before burning up. Again, just used for various voltage levels - no current or power expected from them.

Specific to this BSM discussion is that the mirror LEDs only want to see 9VDC, not 12VDC. I will at my leisure be sourcing another LED display for a mirror sometime in the future.

I suspect many of the modules that ground an input are not capable of sinking AMPS only milliamps.

I generally pierce the insulation and take my measurements with the circuit powered up if I am unsure.

 

Yea you wouldn't typically be wanting to use a test light on a reference or sense circuit unless you were doing a bypass test but for power and ground feeds you want to be loading the circuit and a test light of the appropriate current for what you are testing is much better than using a meter because it proves the circuit can supply current not just show voltage on a meter.
A meter is fine when a circuit is loaded (the module, motor, load, etc is connected and turned on) but that generally requires either backprobing or poking holes in wires which isn't ideal especially on exterior wiring but is generally acceptable as long as you seal the hole up with some liquide tape when you are done.

I try to avoid poking holes if I can but there are times when I do need to use a piercing tool to check a circuit.
Nothing wrong with using a meter to check a circuit under load but most people don't do that, they either check resistance on a wire or voltage with nothing connected and that can really get you in trouble because a single strand of wire (or corrosion in a wire) can show good continuity/voltage but it won't carry any current just like in the video I posted above.

 

I just had a truck in the shop with the same problem, it was the bumper harness. No power to the master or slave, I cut it open and water poured out of it.

 

Hey rusty66 Did you source an entire harness from Toyota, Or did you try to repair?