355 Flashing SDL after I replaced ECUs

Yes. Technistrada (your aftermarket exhaust ECU manufacturer) also offer budget thermocouples if you don't want to buy an OEM thermocouple. I haven't heard of any problems with the Technistrada ECUs (I have one fitted to my 5.2 car for test purposes).
Do you have an OBD2 reader? It should be able to tell you which thermocouple is causing problems.

 

For reference, the OEM P/N is 157501, if you want to order through Ricambi or other local sources.

 

Make sure pins 4 and 5 on the OBD2 port are shorted together and then shorted to earth. Also, don't forget to disarm the immobiliser otherwise the port won't be able to talk to the Motronics ECU.

Good luck!

 

You want to clear the OBD2 error codes after you have replaced the TCU.

 

You mention that you replaced both ECU’s, (CCU’s) there are three.

 

And also, for the 2 on the air pump tray, make sure the connectors are all correctly aligned/connected to their proper ECU.

 

The 3rd is for the bypass. 2 are on the right rear behind the tire. 1 is on the left side top.

 

Of the 2 ECUs on the air pump tray - one is to the TC in the bypass valve, the other for the TC in the passenger (or right side) cat. The 3rd ECU is on the left side and is for the left cat.

 

Replace the thermocouples. They can become intermittent and trigger SDL.

As mentioned above be sure to get TC/SDECU outputs to correct ECU harness connector for bypass and right Cat.

 

Does the bypass thermocouple ever trigger the SDL on a 5.2 car? Or just the CEL? Or are you you just saying this because it’s possible to change the wrong ECU?

 

The Exhaust "Control Station" only amplifies the voltage from the Thermocouple 100 times and sends the amplified signal (analogue) to the ECU. The SDL will normally be triggered if the exhaust temp is too high (ECU receives high voltage signal from the Control Station). However, the SDL will also be triggered if the Thermocouple circuit goes open (if disconnected or due to bad connection or bad Thermocouple) as the Control Station will also send a high voltage signal to the ECU in these cases, as if the exhaust temp is too high.

As suggested, you need to first make sure that the connections to the Control Stations for the bypass valve and for the right side cat are not the wrong way around.

 

Witch two did you replace?

 

Thinking that the left CCU wasn’t changed. JohnK phrased it better, which two were replaced?

 

The ECU's you can swap around to see to see if the code follows it as a troubleshooting step. Does your car have CATs or test pipes?

 

Yes MrJames, there are two ECU (CCU) modules on the plate (Air Injection Devices plate). One module is for the right cat. one is for the secondary (bypass) cats. You can trace the thermocouple leads to easily identify the two. The Technistrada website has good technical information along with parts: https://technistrada.com (main page)
(technical blog)
https://technistrada.com/index.php?rt=content/content&content_id=5

Photo of secondary cats and thermocouple lead. Image Unavailable, Please Login

 

1445 and 1448 are related and they point to the Bypass Circuit (in the middle) malfunction. The likely culprit, and you hope this is it, is the vacuum line controlling the bypass valve is broken or the little aluminum tube feeding that valve is broken. Also a candidate is the vacuum lines running around behind the right side wheel well area, as well as the vacuum switch controlling the vacuum line to the bypass valve.

 

I have a video in my posts of a real time voltage output reading from the Bypass SDECU showing it spiking and causing the CEL. The problem was the thermocouple to the bypass location. Replace it and the sdecu if you want.