I've searched the archives but couldn't find definitive answers. 1. Are the Slow Down light and cylinder bank cutout controlled entirely by the cat ECU or is there some sort of back-and-forth communication between the cat ECU and the main Motronic? 2. If the cat ECU handles all of this, then what is the significance of a 4122 (or 4121 - see next question) "Catalyzer Temp Too High" error code if you get a CEL but no Slow Down light? 3. I've seen the M2.7 4121 error code listed as "Catalyzer Temp ECU" but on this chart it appears as if it is "Catalyzer temp too high". Anyone know which is the correct description for a 4121, given the vagaries and mistakes inherent in Ferrari manuals?? Image Unavailable, Please Login
The cat temp system only gives the too high signal to the ecus immobilizer input. Theres no big communication between these parts. The M2.5 and M2.7 are not designed to messure exhaust temperature. _____________________ Samy
Here is the diference. 4122 Cat temp ECU = the Motronic ECU is not getting a signal from the Cat ECU. This will happen if there is a problem with the connection, like when you unplug the Cat ECU. The engine will still run fine but the Motronic will not be able to monitor the temperature of the cat/s. You shouldn't get a CEL for this, as I believe it is a silent code. Also you may get this code if the Thermocouple goes bad, as the cat ecu gets it's informmation from the thermocouple. So maybe you will get a CEL light? 4121 Cat Temp To High = The Motronic ECU is getting a signal from the Cat ECU that the temperature of the Catalytic Converter/s are too high. This will cause the Motronic to flash the the slow down light. If the Motronic continues to get the "hot" signal from the Cat ECU the light will be steady. If the temp signal continues to read "hot" then the Motronic ECU will shut down that bank of cilynders it is getting the signal from in order to prevent damage to the cat.
Ernie - Nice write-up. On my car, I have neither the thermocouples nor the ECU's. The CEL still works for other functions of the car (I had a Stabilant-cured issue last summer). Needless to say, the only "slow down" message I recieve is from Mrs. JRR in the passenger seat. -Daniel
So can the Motronic store a 4121 code without ever having a slow down light come on?? Sorry for all the questions, I'm just trying to get a handle on the order and logic of the whole ECU system. I know it's Italian, which kinda runs counter to a lot of the mechanical logic I'm used to, but it is a Bosch system, so some Teutonic order should have rubbed off! Unfortunately, here in the Massachusetts, I'm stuck with the cats for the forseeable future.
Well, it's more like Ernie described than that. The Ferrari exhaust ECUs expect just less than 800 ohms resistance between the two thermocouple wires that connect to a cold thermocouple (that's the "good" condition), and anything less than 350 ohms tells an exhaust ECU that the cat is overheating (i.e. the "bad" condition). Outside of those ranges, anything more than 800 ohms tells an exhaust ECU that you've got a broken wire (infiinite resistance) or other problem. Anything less than 350 ohms from your thermocouple signals overheating (e.g. a short circuit has 1 ohm or less of resistance). So resistance values between 800 and 350 ohms are good, while other values will trigger Slow Down and/or CELs. The exhaust ECU's are wired in to the Motronic ECU's at a "shutdown cylinder" connection wire contact pin. Now, whether the exhaust ECU's or the Motronic ECU's are measuring the actual resistance is of some debate...one of those ECU's measures it...and since the Motronic ECU can tell if you've short-circuited or removed your exhaust ECU's, I'd **guess** that it's the Motronic unit that measures the actual resistance.
Well not unless you have a burned out bulb, or one that is unplugged. Because of the possition of the steering wheel the slow down lights are sometimes hard to see. So you can miss the light if it only flashes once.
