Thermocouples, slow down lights, related CEL’s, and how to conquer them...

Rather than make a third box, I decided to just modify the box on my right main thermocuple to also output the signal for the bypass thermocouple circuit.

Here is the schematic. So if you want to eliminate all of your thermocouples and probes, you can just make two boxes.

IC1 = 78L05 5 Volt Regulator .100 mA
C1 = .33 uF
C2 = .33 uF
D1 = 1N4001
D2 = 1N4001
R1 = 200 Ohm Potentiometer
R2 = 200 Ohm Potentiometer

You would be better off getting potentiometers that have alot more turns in them. The ones I used are pretty sensitive to adjustment. I also melt the edge of the part that turns into the housing with just a light touch of the soldering iron once I have them set. This will keep them from vibrating to a different value. You can also use a service cement or fingernail polish. Just don't let it soak down in. You could also use fixed resistors, but you will be at the mercy of their tolerance for how exact your voltage is.
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You must adjust R2 First (the bypass signal). Set this one to about .52 Volts. Then set the other pot to 1.5 Volts for the right main thermocouple signal. R2 has to be set first because it will affect the value of the other one. Double check everything a couple times before you put anything on the pots to keep them from turning (vibration in the car).

You add a connector the same as before, only this time it will just need the blue signal wire. This circuit only drew about 26 mA on my meter. once connected, the computer will draw a tiny bit more, but this is very safe as the 5V regulator will handle 100 mA easily.

You should also put a dab of silicone on each component to the board once you have everything working. You should also silicone the wires coming out of the box as well as the perimeter of the box lid and the screw holes. Also put a few dabs where the board rests in the box to keep the board from vibrating. Basically you want the box water tight.
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Now I will show you how I mounted the boxes. Ignore the dirty engine bay, I have not had time to clean it yet.

You will need to open up the mounting holes of the boxes just a little with a dril bit. They are too small.

On the left side you will or should have two lock nuts that were removed when you took your old ECU out. Put one of these back on the rear most stud and twist it down just past the level of the square bar next to it. Now put a washer over it and make sure the washer face is level with the square tube. This will support the box and let it rest level on the square tube. Make sure you do this right so you don't crack your box when you snug it down.

Now put the box on, then put a washer on the outside, followed by the other lock nut you have.

Zip tie the top to the square tube and snug the nut down at the bottom. Just snug, not too tight.

Plug in the connector and zip tie them together. Make sure your wires aren't resting on anything that moves.
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On the right side, you will need to mark two diagnal holes and drill two small holes and then use a screw to hold it in.

I attached a picture with the screws started to show you about where they will be. This is an aluminum plate, so it is easy to drill. You will need a small 90º angle drill to get in there if you still have the bumper on, or you can use an air ratchet to drive self tappers.

Again make sure you zip tie the connectors together and I recommend zip tieing the wires in the area together to make it look clean.
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Now, I drove the car for about 40 miles after the install. A bunch of in town and highway. I never cleared any codes from before because it did not have any . At this point the computer was past the learning time (usually about 50 miles) and I have no codes and no slow down lights.

So, thermocouples and thermocouple ECU's are conquered

 

Yes, the slow down light should come on for a bit when you first turn the car on. Same as your other warning lights. See attached text from WS manual.
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Here is some text I found odd since my car and others seem to not care about seeing a thermocouple temperature change from cold to hot when the bypass opens...

Seems to me like this is untrue and that it possibly is just looking for over temp cats when it is open or it is doing some sort of comparison to the main thermocouples and as long as they are in the safe range and the bypass is not too hot, then it doesn't care....who knows...all I know is what I did works so far

The part about the bypass being controlled by the ECU is true, but the rest......not so sure about that since my setup and others proves otherwise.
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Yeah I was thinking about selling them. I have no use for them at this point. I was going to add them to my eBay collection of Ferrari parts for sale LOL. PM me about it.

 

Since Cavlino wanted to buy my thermocouple ECU's I wanted to test them all before I sent them. I only had the one out up to this point and the bypass was a newer one, but when I removed them all I had a black potted one on the left. I discovered that my left main ECU was outputing about 1 volt with the thermocouple at room temp. It should be about .52 Volts.

So, I was pushing and pulling on the connectors. Something I always do when troubleshooting electronics like this. I discovered that the signal would fall to normal as I did this.

This told me there were bad solder joints on the circuit board (common in auto electronics due to vibration, hot and cold cycles, etc. This is also the most common thing you pay for when you send modules out to get rebuilt (Like ABS modules etc).

So, now that you did my above tests and discovered you have a bad thermocouple ECU, and you don't want to ditch the troublesome parts. Do you want to fix it yourself? Here are the instructions for that. There can be other failures, but I bet this fixes 80% of them

First you get your 1/4" rounded deburring bit in your die grinder.

Next grind down to where you just touch the tips of the connector pins and expose them on each end of the box. as shown in the picture.
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Next you can just use a heavy duty dental pick and pluck out the surrounding potting material. It comes out pretty easily. Be careful not to dig into a trace or damage the board.

Next, use something to gently scrape the green coating from the traces that connect to the where the pins are soldered. This will allow the solder to flow out onto the trace area as well as around the pin and give a stronger solder joint.

The solder joints don't look as bad as some I see, but they are bad! Once the solder just makes a nearly microscopic crack around the pin and it oxidizes (or whatever happens to the metal chemically), then you get an intermittent or open connection as I was seeing.

First two pictures are before shots, second two are after.

After you have done this, solder the pins and use the tip of your iron to rub around the connector pin and clean the impurities off of it as it is heated up until the solder flows onto it good.

At this point it would probobly be good enough, but I desoldered everything to pull the impurities off and then resoldered it again.

Once you have done this, test your unit again. There is a good chance it will work perfectly again!
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Now if it does work, get some of the black silicone they sell at the autoparts store (mostly used for engines etc) and fill in the cavities you made. Also go around the outside edge of where the potting meets the plastic and all the way around the connectors.

Now you have a thermocouple ECU that will probobly last longer than it did the first time when it was wave soldered by a machine. Also, if they were following any ROHS back then, and your not using lead free solder to make the repair, then it will be even stronger yet.
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Now you will have 6 and know how to repair what probobly ails most of them. You should never have to buy another one again I do still have to sell my 3 thermocouples though. If anyone needs those, let me know. They are all tested.

Imagine all the Cat ECU's that got thrown away or are still laying around that could possibly be repaired easily.....

If anyone is having an intermittent problem, be sure to wiggle the connectors and bounce the box around when you are doing your intitial checks on the bench. It may work fine on the bench just sitting there but act up when it's abused a little to expose the intermittent connection problem. You could potentially put it back in thinking it is good if you don't do this and then you will be really confused as to why your having a problem still. You may also want to warm it up with a heat gun while it is powered up to see if there is any reaction (don't melt it!).

Now, hopefully this is about all I will have to do on thermocouples. If your actual thermocouple is bad, forget it. I am not trying to fix those

 

I think you have some other issues going on. I would start a new thread with your issues. I cannot access my codes list until I get home. You may have more than one issue.

 

The module is the same part number. The thermocouples are probobly the same type, but may have some difference such as length (not sure, but PN is different).

All of the above stuff should apply to most cars using the 179278 module.

 

P1445
P1449
P1448

Those are all thermocouple related codes. First two are main thermocouples and the 1448 is bypass. I suspect other conditions can cause a 1448 when there is not a real problem with the bypass thermocouple. I got a 1448 when I was having cat efficiency codes and as soon as I resolved that, it went away. I also tested my bypass thermocouple and ECU and they were always good.

Also, as several people have seen now, if your motronics is seeing a signal it likes from the main cat thermocouple ecu's it will not care if the bypass thermocouple is dangling in the wind. However, if your bypass thermocouple is bad or the ECU is bad, even dangling in the wind will probobly still cause a code. The thermocouple and ECU has to be good or you need to be sending a simulated voltage like I am.

I would chase down your other codes first and then see what happens to the 1448 or bench test your bypass thermocouple and ECU if you want. Sorry I forgot to look at my code list last night. I still recommend starting a new thread focusing on your particular issues.