Speed Sensor Errors

[sheptastic]

While coming to a stop the GX gave a little shudder (like the ABS activated) and then the ABS, BRAKE, Traction Control, and triangle warning lights came on with a check BSM system message. On the way home the warning lights went off. Then, after 100+ miles, same thing...shudder at low speed while coming to a stop and the same lights are on.

OBD Link MX+ reports C1403 Malfunction in Rear Speed Sensor RH Circuit, C1407 Open or Short in Rear Speed Sensor RH Circuit, C1415 Rear Speed Sensor RH Circuit Output, 2x C1A45 Vehicle Speed Sensor codes (and a P1605 Rough Idling and B15EC, which I assume are unrelated).

While I was rotating my tires, I pulled the passenger rear speed sensor and it was clean (looked OK). I took off the electrical connector, which looked good with no corrosion, etc. There were no obvious issues with the wire along the rear axle.

Lexus dealer replaced the pads, rotors, and brake fluid a year or so ago. The brake fluid is halfway between the min and max lines in the reservoir.

Is there anything I can do to troubleshoot/repair this? I now live about 100 miles from the nearest Lexus dealer and I haven't checked to see if the local Toyota dealer would do any service.

 

[gnob]

check resistance on the sensor itself and wires back to the module. also shine a light through the sensor hole and nake sure the ring doesn't have damage or something stuck to it. check for bearing play.

 

[sheptastic]

I couldn't detect any play in either rear wheel bearing.
Driver's side:
Sensor measured 334.4 k ohm
Wire measured 125.3 k ohm
There was a bit of brown moisture on the sensor. It wasn't oily/greasy.

Passenger side:
Sensor measured 331.5 k ohm
Wire started around 78-80 k ohm and increased (about 0.1 k ohm/2 seconds) until it reached about 96 k ohm. The rate of increase slowed as it got higher.

The focus wasn't great and I'm not sure what I'm looking for in the sensor hole. I didn't see anything obvious and no burnt grease like the bad bearing in this post: 2011 gx460 trac/abs/lo lights troubleshooting - ClubLexus - Lexus Forum Discussion - https://www.clublexus.com/forums/gx-2nd-gen-2010-2023/970574-2011-gx460-trac-abs-lo-lights-troubleshooting.html. Maybe an issue with the wire or computer?

 

[sheptastic]

I have a crackpot theory, if the symptoms I'm having could be due to an intermittent short.

Without anything meaningful to do, I decided to vacuum the interior where I found the driver's floor mat and carpet were wet. I pulled the lower panel where the fuse box is and there was some moisture in there as well. Could I have a sunroof drain leak that caused a misreading in the speed sensor? I considered disconnecting the battery and pulling the wiring connectors loose that I can see to help make sure they dry out. Currently just sitting with the windows open.

@Acrad, is there anything in that location that could affect that sensor's reading or ABS?

 

[r2m]

I have a crackpot theory, if the symptoms I'm having could be due to an intermittent short.

Without anything meaningful to do, I decided to vacuum the interior where I found the driver's floor mat and carpet were wet. I pulled the lower panel where the fuse box is and there was some moisture in there as well. Could I have a sunroof drain leak that caused a misreading in the speed sensor? I considered disconnecting the battery and pulling the wiring connectors loose that I can see to help make sure they dry out. Currently just sitting with the windows open.

@Acrad, is there anything in that location that could affect that sensor's reading or ABS?

Doesn't sound all that "crackpot" at all. Sounds very reasonable for it to be a short, especially if it's sporadic.
How often does hit happen? Is it a regular pattern, like going up a hill, accelerating, stopping, or something like that when it comes on?
The best thing to try and do is get so it's repeatable and under what instances cause it. Only then can you get a good picture of the issue.

 

[sheptastic]

I'm leaning toward a clogged sunroof vent at this point. Not an exact timeline, but we got a decent rain and the issue arose the next day. After a few days the dash lights went out (seems to have resolved itself). I then went through the carwash and the lights came back on a few miles down the road. The dash lights were on yesterday when I found the water on the driver's side floor. After airing out the GX for several hours, with the fuse block cover removed, the dash lights went out after driving a few feet and stayed off after a couple mile drive.

I found some debris in the sunroof opening and some leaf bits in the driver's side drain opening. I cleaned all that out and ran some weed trimmer string down the drain tubes. Driver's went down 6' and passenger's went down 7'. I think my string is wimpy, so I also ran some stranded 12GA wire through it and got to the same point. Both seemed to stop and I never saw either come out under the GX. Am I hitting a blockage, or is there something below the end of the drain tube?

I want to make sure the drains are clear and replace the sunroof seal. Looks like I need to take the glass out to do that. Anyone have experience replacing the seal?

 

[sheptastic]

My issue really seemed to be water related. I've had no problems since the floor and under the driver's side A pillar dried out. I thoroughly cleaned the area around the sunroof, especially the front channel where the drains are and the roof where the sunroof seals. I got a new sunroof seal for around $40 and replaced that as well. The old one was pretty grimy and much less pliable than the new one.

Not for the GX, but this video helped with the seal replacement. I didn't need to use water like he did. I just rocked it up and down until it was seated evenly all the way around.

Hopefully it's all good now. Going into fall, I'll find out soon enough.

Edit: I forgot to mention that I used a funnel to pour water into the front drains after I ran wire through them and it came out under the GX.