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Hi everyone. I purchased my 16 RX late december. All of a sudden my BSM (blind spot monitoring) and RCTA (rear cross traffic alert) weren't lit up as "on" anymore. I went to my settings on my steering wheel to turn it back on, and there wash;t the option anymore to turn back on, WHAT?! I looked at the manual, said maybe the sensors might be dirty, so I washed it and let a few days pass, with everyday I tried to get it to come back on. No luck. Called my dealership (which they think it was just me not being able to work it properly) and they told me to swing on by and they'd help me. I told them it was broken but they said nonsense, that I probably didn't locate the right area to fix it. OKAY, right! I got there for my appointment and sure enough it wasn't responding for them either. So now I have a loaner and waiting for them to tell me what they're going to do. Guy said this is the first he's seen do this..ugh! Anyone else have come across this?? Also, I hear a gurgling noise when the air is on only, so I told them to look at that too.
First hearing about it but most likely the CPU that controls those systems need to get swapped out.
Since you are getting taken care of I would not worry too much about it.
Just fixed one of these. Might be more common for outdoor parked vehicles in high moisture climate.
Background
Friend's car. 2018 RX450h 46k miles. Day time parked outside in rainy Seattle weather. Night time parked in carport.
Problem
When starting, passenger side BSM light up briefly. driver side BSM doesn't light up, followed by BSM error on dash.
Dealer read code C1AB4 - Open in Outer Mirror Indicator (Master). Quoted $700 to diagnose wiring fault before providing repair quote. Friend brought it to me
Diagnostics
Initial google research showed Toyota Sequoia, Avalon of similar year had a TSB for C1AB4 code solved by dealer upgrading BSM sensor software. But Lexus has no such TSB. Turns out Toyotas are Denso BSM while Lexus is Continental. So no quick solution haha.
I have Techstream and confirmed C1AB4 code
Consulted service manual actions for this code and wiring diagrams
Basically the driver side BSM module (master, passenger side is slave - for LH cars) detect higher than expected resistance to the driver side mirror BSM light. This detection takes place when car first starts, thats why BSM light on mirror briefly on startup while its testing.
Service Manual says to check resistance between all connector points for this signal line (and the ground). Every hop between 2 connections must be < 1 ohm.
Since this is safety feature. <= 1ohm per connection hop is understandable. But also at higher risk to be disabled by slightest corrosion
Eventually found 6.5ohms on BSM light ground circuit through the connector under rubber accordion boot between the driver door and body. Ground is probably shared by other signals but BSM light requires ultra low resistance for safety circuit as noted above.
Connector is protected by rubber boot but this is high moisture area as water can run in this region between the door and body
Fix
Disconnected connector, sprayed contact cleaner, reconnect, reattach with rubber moisture protection boot along with thin coat of lithium grease to aid in moisture protection
Info and Pics
Techstream is Toyota factory diagnostic tool. Need special OBD2 cable (< $10 on aliexpress/ebay) and software (often posted on mhhauto.com, @Autokent for key + OBD2 cable driver)
Chilton's online library for wiring diagram (My local library provide access to auto repair info) Wiring diagram attached.
Tested resistance on ground path between pin 7 on N4 connector (behind driver door panel) through NS1 connector to SA ground point (behind B-Pillar trim panel)
Release 4 clips holding NS1 to body (release upper or lower pair first followed by next pair, released ones wants to clip back in so be patient)
Unclip (use a flat blade to release) black handle which tightly clamps the NS1 connector 2 halves together
Release black handle, pull 2 halves of NS1 apart. Very tight space
Spray clean with contact cleaner. Wait to dry, Wrap boot around female half. Reassemble connector. Push back into pillar cavity.
Optional : Add lithium grease for added moisture protection. Not easy, very tight space. Can consider practicing assembly before applying grease. I added grease before assembling connector (can be messy) Could consider adding grease after connector reassembly on boot or pillar frame (harder to reach backside) Note that wires on the connectors will be twisting and bend sharply during the reassembly process so don't want to do too many times.
Ignore the disassembled dash panels. Was just figuring how how to get to NS1 connector. Unnecessary.
BSM & RCM (Remote Control Mirror) wiring diagrams attached. I noticed some wiring colors mismatched my car.
Could also have corrosion on the BSM+ line so check that as well.
Same error can occur on passenger side (C1AB5 code) and should be same repair process. I didn't do any preventive cleaning in case factory install already had moisture seal aid. Driver side on this car was previously removed by body shop during door panel collision repair.
I also removed the mirror glass to check BSM LED (9 voltage battery) and since it is also exposed to the element, contact cleaned these as well. Here is mirror glass removal direction
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Bsm & rcta failure!
