348 Loss power! Ecu code: 4121

I had the same a while back. Watching the error switch sides, just like in your case, was pretty convincing to me that the issue was with the Cat ECU. At the time, a new one would have cost about $900. Also, I need to add that my issue (also gave the 4121 error) was very sporadic. It would be fine for days, then the error would appear and the resulting power loss as one bank of cylinders shut down, but after 15 or 20 seconds, the error would turn off and power would re-engage.

Anyway, after about six or eight weeks of checking ebay, I got lucky and found one for sale at a drastically reduced rate. Supposedly, it came from an early (1995 Motronic 2.7) 355 that had been totaled in a front end collision.

Try checking some of those shops that specialize in parting out the bits that are salvageable from smashed Ferraris. If you have the time and patience... Ebay may pay off. It did for me.

 

Did you disconnect the heat sensor from the cat ecu (small plug) or did you disconnect the cat ecu from the main ecu (larger plug)? If it was the heat sensor, a faulty cat sensor can still be sending bad data to the ecu and shutting down the bank.

If you did in fact disconnect the cat ecu, you would still get an error but it should not be shutting down the bank - you have another issue if that is the case.

 

I don't know enough about reading spark plugs to say if you have another problem or not - here is some reading on the subject which may be of help: http://www.ferrarichat.com/forum/showthread.php?t=121401

Could the plugs on the 1/4 side be the result of a bank cutting in and out? You might try disconnecting both your cat ecus (to prevent either bank from a shutdown), going for a hard run and then pulling your plugs and reading them.

Your troubleshooting seems to indicate you have one bad cat ecu; with what they cost I would only replace what is necessary.

 

Okay something doesn't sound right.

Try this and then let us know what happens. COMPLETELY remove BOTH cat ecu's, and I mean take them all the way out of the engine bay and put them on the bench, out. Then disconnect the battery for about 30 seconds, reconnect it and let the car go through warm up procedure (letting it just sit and idle for about 15 minutes). Take it for a spin and tell us what happens then.

 

Check the relay for the fuel pump.

 

What he said. I would also check the ECU relay.

 

Any follow-up on this thread. I am having the same problem. What was the problem and the outcome? Thanks.

 

Please state your exact problem and any codes or lights so that we may help you

 

Really like how your 348 looks in your profile picture, best I've seen. I think it's the wheels being black.

Ernie helped me with my 355, I was able to just unplug the plug from the ecu to the cat ecu and no power loss, only CELs. Before, I was getting a bank shutdown about once per drive, then the last one really shut me down. It was way more reduced than previous but I was still able to limp 2 miles to a friends house where I let it sit for half hour then all was fine.

 

Hey after a major service like belt you need to disconnect the batterie for 35 sec to 2 min after tstart the engine with nothing electronic on for 10 min to let the fan goes on at the idle no gas no ac no radio the get the factory programmation of the ecu I had 2 348 at my job and get the code 4121 and after that the code disappear

 

Having same issues- I know this is an old thread but any solution found for this?

 

Same issues as which poster? For which car? What engine management system do you have?

What have you done so far to the car? Checked the codes? Swapped the thermocouple ECUs to see if you get a different light? Disconnected the thermocouple ECUs' larger plugs (with battery reset and long idle) to see if the problem went away? Checked the pump relays? Checked the plugs on the bad side?

You don't have to do everything at once.

 

So you have two issues at the moment (and two different codes)?

https://www.ferrarichat.com/forum/posts/149377802/