Body ECU DTC 41 (NHW11)

Not because of any apparent problem, but just out of curiosity, I jumpered TC to CG to see if there were any diagnostic codes from ECU's I couldn't see with my generic scanner. The Body ECU reported a 41.

According to The Book, this is a switch test for the stop light switch. You should see 41 with the switch activated (if not, there's an open), and not see 41 otherwise (if you do, the switch should be stuck or shorted). DTCs 21 and 22 are described the same way with respect to the driver door window and lock switches, and they work as described.

But I don't understand this 41, because I can't find any problem with the stop light switch. It is brand new since I installed the cruise kit a couple of weeks ago, and the stop lights work, the cruise works, and the shift lock works, all things that rely on that switch. The 41 code stays active whether the brake is depressed or released.

I am wondering if there was a misprint in the book (wouldn't be the first one I've found) and the 41 DTC really refers to some completely different circuit. Maybe they issued a correction as a TSB or something. Ring any bells for anyone?

The Body ECU doesn't seem to have any special procedure for clearing codes; they go away when the underlying condition does.

-Chap

 

It now occurs to me that since there's a new Classic forum, I'm not sure what's the best place to post technical, Classic, questions....

-Chap

 

I guess this probably should be moved into the Gen 1 forum.

I looked at this again tonight. It's obviously been there for 4½ years without anything at all seeming to be wrong with my stop lights, but it was the only code left so it offended me somehow.

The body ECU is the entity speaking to you through the door-ajar light if TC and CG are jumpered together with the ignition switch on. If it is happy and content, it speaks with a steady fast blink. But it has been giving me (four blinks) (pause) (one blink) ... the 41 code that should be seen when the brake switch is activated. Or, if it shows up when the brakes aren't activated, it should mean the switch is stuck. Only I've never seen it change no matter what I do with the brake switch (or the parking brake switch, for good measure, or both of them together), and everything else that depends on both switches has always been working.

Pretty much by accident I noticed something that makes me think there's just a bug in the body ECU.

If I generate a 22 code (by holding the door unlock button long enough to seem stuck) and then let the button go, the 41 code goes away when the 22 does.

If I generate a 22 by holding the door lock button down, a 22 and a 41 are shown. When I let the button up, the 22 goes away, but the 41 stays (until I generate another 22 using the unlock button).

Whether the 41 is present or cleared, it never seems to have anything to do with brake switches.

Now I'm sort of idly speculating about what sort of misplaced branches or something in the ECU firmware might have made this code end up depending on the lock buttons instead of what it was supposed to depend on. But at least I now know how to make it go away.

-Chap

 

I finally got to the bottom of it, years later, but forgot to update this thread. Yes, it is a mistake in the manual. I should have caught on sooner, because the code is listed among several other codes that have to do with the driver's door, and nothing remotely to do with the stop light switch.

It tests the driver's door unlock detection switch (D13 pin 4), which is called "LSWD" (P9 pin 10) at the power-window/door-lock master switch, which communicates its state by messages over its MPX1 line (P9 pin 18) to the Body ECU (signal RX, B8 pin 6). All this is done so the Body ECU can warn you if it thinks you might be locking the key in the car.

Code 41 should be present when the driver's door is locked, absent when it is unlocked. That's the long and short of it.

Some overworked translator probably thought whatever word means "lock" in Japanese was the same as "stop" in English and decided it must have to do with the stop lights.

-Chap

 

This thread is about blink codes from the Body ECU (they blink on the door-ajar light).

If you are getting blink codes on the brake, ABS, VSC lights, those codes are coming from the Skid Control/braking ECU, and there are already lots of other threads on that.

It would be best if you either add to one of those existing threads, or start a new one, so nobody needs to add to this Body ECU thread with responses about your Skid ECU.

The sure-fire, one-step way to find the meaning of your skid/brake codes (if you find a forum search too hit-or-miss) is to look them up in the repair manual at techinfo.toyota.com.

-Chap