Nonio

Hi,

Need some help. Brake Light Warning Failure light is on in the dash but all lights are working great.

Checked all light sensors and all are great.

Been all over the service manual pdf but cannot find complete circuit.

Where to sensor's connections go to ?

Help appreciated !

timzer

check brake fluid level

Nonio

It's fine. It's the rear brake light indicator that comes on.
HELP needed.

timzer

check the brake petal there should be a switch check if it press it and see how it goes

brakedrum

Mine has been on for months, and I'm pretty sure I know what's causing it, but just haven't decided which route to go. The brake lamps have a so-called "stop lamp failure sensor" inside the brake lamp assembly at the back of the car inside the trunk on the drivers side under the little panel. On CB7, it's a small brownish box with 2 screws holding it on, it has a plug with 5 wires going into it. That's the thing that signals the presence of a bad bulb and makes the light dash indicator glow and the part that I think goes bad. Unfortunately I have no way to be sure.

The brown housing covers a small circuit board with only one transistor/resistor/diode or whatever it's called. There are two small spools of copper wire that are also soldered into onto the electricals of the board. Must be one for each brake lamp. On the passenger side, there is a black box that looks almost identical. I'm not sure but I think that one is for the reverse (back up) lights. Or it's involved in this same thing. I just don't know enough about it to be sure. The brown box is my suspect, though.

Honda lists the part as 37540-SM4-A01 and, or 37540-SM4-003 $20-$30. I had mine off a while ago, but there's nothing that can be visually detected-- especially not by a non electrical person-like me. Maybe somebody who knows how to test circuits could take theirs off and check resistance and see if the part is up to snuff. Of course determining the spec's on the part is another matter. If the little transistor/resistor/diode is bad, perhaps an electrical guru could test it.

Update: Unplugging that box does NOT make the dash light turn off. Maybe the absence of the box is the same as an open closed/open circuit and a fault condition.

Either way, the problem is so widespread with Honda Accords that it must be a common part that's causing it, instead of assuming all those owners having bulbs that are out-of-spec. That also makes me feel its not worth crawling around in the thistle and grime at my junkyard trying take one of these off and old wreck, because it's probably bad or about to go bad.

brakedrum

This is a picture of my 93 Haynes manual that shows the wire flow on that circuit. Apparently, there are two Brake Light Sensors one for each side, but it is the left one that has a WHT-GRN wire that goes directly to the dashboard cluster. It is also connected to the other sensor with a GRN-WHT wire and a GRN wire. I guess either sensor could be giving the fault and making the dash indicator glow, but I'm still sticking with the left side one as my suspect. Never uploaded a scanned image here but going to give it a shot. The coupe/sedan is the right column on this page:

Nonio

Does this schematic include any of the rear lights' sensors/circuit ?

PT-Tuner.com

I have had my brake lamp indicator come on even though all my bulbs were working. I replaced them all at once, and the issue hasn't come back.

brakedrum

I don't think so, Nonio. That looks like Anti Lock Brake system schematic. The picture I posted shows where the wires go from all the back brake light electrical fittings. The bottom right corner of that schematic depicts the brown box that I photographed. That's the thing that supposedly senses a bad bulb and makes the "Brake Lamp" indicator glow on the dash.

PT-Tuner, Although I'm still looking into those sensors, what you did is probably the answer. Bulbs that have been installed a long time that still glow but are no longer up to proper spec.

Nonio

Serious ?

That means that the sensors are there to pickup rather more info than just if the bulb works or not ? That's amazing !

I had no idea, I'll give that a shot, trying out the complete replacement before anything else.

How many of those brown boxes are there to be found then ?
Do they send the info direct to the dash or is there some sort of other box in the middle ?
Can these bulb sensors be overriden as to let the make belive the bulbs are great ? This might sound silly but I'd rather pull them all out and just connect the right wires so it wouldn't come on the dash anymore. Possible ?

PT-Tuner.com

I know there is a relatively simple modification you can make in order keep the dash indicator from coming on anymore, I just don't know the specifics at the moment, as my normal resource cb7tuner.com is down at the time of posting.

Nonio

Thanks ! Will you paste it over here when CB7tuner.com comes back on ?

brakedrum

On my 93 EX the brown sensor is on the rear left side right beside the holders for the bulbs. The black sensor is on the right side in the same spot (see pictures). They work together in a loop checking those stop light (braking) bulbs (including the high-mounted one) for continuity, impedance, ohm's or whatever they check. When a fault is detected, the brown one makes the dash indicator come on. The dash indicator will also come on if there is a fault with either of the sensors. But there is no way to know if the fault is with the bulbs or the sensor(s) and if a sensor is the problem there's no way to know which one. If Honda would take returns on electronic parts, I would buy them and plug them in to see what happens. Meanwhile my brake lamp indicator is still lit.

brakedrum

Maybe there is some simple bypass as PTTuner said. I do know that I pulled the plug on both sensors and my dash indicator still glowed. Also the brake lights didn't work at all with the plugs pulled on the sensors. Those sensors are integrated in the whole stop light system. When I think about it, a burned out stop light is a pretty important thing, and the only way the driver will immediately be warned is with a red light on the dash. The mystery surrounds what to do when all the bulbs still burn. I'm going to replace working high-mount bulb tomorrow and see what happens. I bet there's a way to check those sensors, but there is little info available on them. The proper spec's and which pins to probe with a multimeter would be needed in order to check them.

PT-Tuner.com

Heres a quote from scudwieser on cb7tuner.com:

on the drivers side brown box you just need to splice the white wire with the green stripe into the solid black wire. after you cut the white/green wire did you splice in the side coming from the brown box or coming from the larger connector on the harness? i spliced in the wire coming from the harness and left the one coming from the box capped off and my dash light hasnt come on since.

Ah the joys of google and the "cache:url" feature, although most of what google had cached, has been replaced with "account suspended".

brakedrum

Yeah. That wire is the one that is connected to the "brake lamp" dash bulb socket. By splicing it, the sensors would be able to sense, but would not be able to light up the dash. I'm sort of fanatical about keeping my CB7 whole, though, so I won't do any splicing, but it's nice to know how to do it. If it comes to it, I'm just going to replace the sensors starting with the brown one and see what happens. If it is a failed sensor, I can honestly say that sensor was good for over 17 years.

Nonio

Pt.Tuner, that's some really cool piece of info/advice.

However, one little detail doesn't click. If it's the driver's side sensor that has to have the white/green wire sliced is it still a brown box ? As we can see on Brakedrum's pics, on his car there's a brown one on the passenger side and a black on the driver's.

Do I just slice that wire on one of the sides and clip it with the black one or does it have to be done on both sides ?

Thanks again for all the help.

brakedrum

The two sensors work in a loop, but that one white-green wire coming out of the brown box is the wire that triggers the light on the dashboard.

I'm not going to try the workaround, because I like what those sensors do. I have had that dash light warn me of bad bulbs a number of times over the years, and there was always a burned out bulb present when the dash light would come on. Now that the dash light is coming on with no burned out bulb, I suspect that the sensor(s) is bad.

Nothing more important on the back of the car than properly working brake lights, especially in highway driving.

PT-Tuner.com

You know about how easily our main relay can be fixed right? Its as simple as desoldering/resoldering each of the contact points, as the solder cracks over time.

Maybe the solder/connection points are messing with the resistance of the circuit, and that is whats causing the problem. I would say give it a try, it would be a simple fix, and it doesn't ever really get cheaper then this. Just a thought

brakedrum

When I had those sensors out, I kept looking at the soldering and thinking about what you just said. I just don't know what to look for. The copper wire spools are the actual sensors. The brown box has one for each left side bulb and the black one has one for each right side bulb and another for the high-mounted bulb. I guess it's possible the copper or whatever it surrounds has changed over time, and cant sense properly anymore.

I just read another recent thread on this topic and the guy just reported back that he cleaned his bulb contacts with a wire brush and solved the problem. I'm going to poke around the kitchen again to see if I can find something to do a little wire brushing on my contacts.

PT-Tuner.com

Rust/corrosion does add extra resistance to the circuit, which could very well cause "false readings".

brakedrum

Examining the design of the brown box, I notice the wire that goes to the dash cluster light is connected directly to that lone diode/resistor/capacitor/transistor that is soldered onto the board inside the brown box. Is it possible to identify that electronic part using the numbers on it, and then testing the part against known spec's for it, if such spec's are documented somewhere? Here's another look at it:

PT-Tuner.com

If you can get all the numbers off it, then yes.

brakedrum

Okay, here they are: P10G
-------------------------- 19242

I youtubed some stuff up and found that thing is a diode and current should only flow one way on it. I multimetered it, with it still on the board, and with the red probe on the black side and and black probe on grey side, I get about 640 Ohms, but no reading at all when reversing the probes. If the spec's on the diode are about what I measured, then I guess the diode is functioning properly?

PT-Tuner.com

It sounds like the diode is working normally; another way to think of it is a one way valve.