355 Code P1448 when wiring exhaust valve open 5.2

So does a valve remote controller trigger a code as well?

You’ve got the X-OST exhaust on? (I love saying that .

 

Too much anecdotal evidence. No one knows the ECU logic for the P1448 code:
Some say the logic can be fooled by a dummy Thermocouple ECU. I vaguely recall someone was experimenting with a variable resistor to generate different temperatures for the Motronic ECU to use (no update).
Some say the logic can be fooled by dangling the thermocouple in the air (Doesn't make sense at all as the WSM says the thermocouple needs to see a temperature change with the valve open)

Someone said that the ECU doesn't look at the resistance of the bypass valve solenoid coil as part of fault code generation. Maybe someone can create a resistance switching circuit in parallel with the bypass valve solenoid circuit (see diagram below) i.e. a circuit which feeds artificial temperature values back to the Motronic ECU when a command is sent to the solenoid valve to open the bypass valve.

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R1 and R2 could simulate the low and high temperatures respectively. Of course, knowing the resistances would be the hard part. Perhaps the resistance switching circuit could be plugged into the solenoid valve connector (and the solenoid valve disabled completely).

By the way, @wbt (of Technistrada.com) was looking into making a dummy bypass thermocouple ECU (and was looking for volunteers).

https://www.ferrarichat.com/forum/posts/146748672/

 

I have tried at length to bypass the centre cat ECU with a dummy voltage. Nothing worked. Eventually P1448 came back. It seems there is some comparative logic going on to determine if the valve is working. We tried a custom made variable voltage cat ecu at every 0.1v increment from 0-5v. No joy. Dangling the thermocouple will certainly not work (this will give a constant 0.5v signal). Gothspeed offered one for sale some time ago but I cannot see how it worked reliably.

My recommendation is to keep the centre valve and ecu/thermocouple in place and for de-catted cars bypass the left and right hand sides. If you want more noise investigate some rear exhaust can upgrades. I fitted tubi rear boxes in both my 355 and 360 and they sound fantastic.

2.7 cars no issue - no centre cat ecu fitted to them.

 

That's why I was wondering if my switchable resistance circuit would work. Or does the zener determine the voltage (and the resistance only the current)?

 

The zener would cause a set voltage drop in either state. I’m not sure this is necessary.

I think you’d want a resistor DIVIDER at different ratio on the two relay outputs to achieve what you’re after. I’d imagine the input to the ecu is pretty high impedance so the series resistor alone will have negligible drops.


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simply remove the thermoprobe, cap the whole. no more code.

Its purpose is only to tattle if the valve is left open. it has no other purpose (i.e. fuel trims etc)
tested 7 years by me and many of us. works fine

 

The computer is smart enough to determine if there is hot exhaust going through the center channel when the valve is open, and no exhaust gas when the valve is closed. Unless you change the firmware, there is no way to fake the system from throwing a 1448 code.

 

From Ferrari. The Motronic is designed to, based on data from probe determine if valve is open when it is supposed to be open and closed if it is supposed to be closed. Removing or disconnecting the probe will not fix that. I know with certainty that not every 5.2 car does that but most do. Do not know if it is a malfunction or if different software versions it was left out.

 

This discussion comes up ever few months, those who have ~read~ about it are on one side, those who actually are doing to on the other side of the argument.
That probe is there to report if the valve fails open, triggering a p1448 code. That happens when the probe is still reporting a voltage (due to heat) when the RPM and TPS are saying it should be closed. A cold probe (example, it removed from the exhaust) will not trigger a code simply because it never gets hot. The ECU is not looking for a cold probe, it doesnt care if it probe stays cold.
Anyway, Goth was the one who enlighten us to this, I and others have been happily running this set up for years. My system works 100% correct, if I install the probe, I get a p1448 code like its designed.
Those who want to test it, it require almost zero effort. Just unscrew it. If its doesn't work, plug it back in, come back here and bi*** lol.

 

on the muffler, inches past the bypass valve. there is a thermoprobe. I believe its like a 13mm nut holding it in. unscrew it. zip tie it safely out of the way. Cap the hole with a $1 1/4 or 3/8 NPT cap from the hardware store. Clear your current code and drive it.
Now if if your probe ECU is bad, and thats why it giving you the code, this wont fix that.

 

Wondering why Bosch would design it like this. Was their priority environmental protection?

And why can't a constant temperature dummy signal stop the message appearing? (see post #4)

 

No emission implications. It was present for diagnosis purposes. There are a few but very few fault codes only for repair purposes.

Because it isn't designed that way. I didn't just read about it. I was in a funny yellow building in Maranello talking to an engineer.

 

I forgot. All their engineers are idiots. I am better off listening to nameless people on the internet.

 

I'll stick my neck out here. I don't see why this is so complicated. The bypass TC senses the temperature of the exhaust behind the valve. Hot = open, cool = closed. The main ECU know whether the bypass valve is supposed to be opened of closed based on gear, RPM and throttle position. So simple: Is BPV supposed to be open? {Yes. Is TC hot? [Yes. OK. ; No. Set code.]} ; {No. Is TC cold? [Yes. OK. ; No. Set code]}

 

That's the way it probably should be designed. Of course, you have to figure out what is "cold" and what is "hot". I imagine the air in the muffler would get very warm (generally) after a long drive even with the bypass valve closed. There are no checkvalves or sealed sections in the muffler.

Are you specifically referring to my comment "and why can't a constant temperature dummy signal stop the message appearing"?

I don't see any difference between hanging the thermocouple in the air (with no temperature variations due to exhaust gases) and simulating a similar (ambient) temperature with a voltage. You can simulate a main cat temperature with a fixed voltage (and the system is happy). On the 348 and 360, there is further logic. You can't fool the ECUs on these.

 

I have removed all the TC and ECU out of my car for SDL testing. I cannot remember the specifics, but a working TC/ECU will report a certain voltage, say .5v when its cold. put a torch on it and and the volts will rise. I remember it being quite slow and really not changing at all until 400f+.
anyway, what is cold when the valve is closed? I guarantee its not 60f lol. its probably still constantly varying between 300-600f. So its not looking for cold situation to report a trouble code, only hot, like 1000f for an extended amount of time.

 

No. Making fun of someone else.

 

Its what I have been saying. And is why if left out or disconnected you get a CEL.

 

I'm pretty sure that's directed at gothspeed and myself

 

@wbt and experimenters simulated a range of temperatures from 50F upwards by sending voltages to the Motronics ECU (as the thermocouple ECU does), but they still got a bypass code.

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Your floating thermocouple is producing a relatively cold (engine bay temperature) which has been simulated by a number of fixed voltages in wbt's experiments. Why does your floating thermocouple not generate a code (if it is causing the thermocouple ECU to produce the same voltages)?