My 1990 348 has negative ground disconnect. Does activating this reset the ecu?
Vince, I will disconnect the battery entirely when I purposely want to erase the codes, but does using the negative ground routinely erase the codes every time I use it?
This is a good question. Personally, I don't believe that disconnecting the battery will erase any STORED codes in the Motronic ECU's. Error codes can be erased from the memory of the Motronic ECU unit by following the steps described on page C79 of the workshop manual, at the end of the self-diagnosis procedure. When you say "reset the ECU", yes, you should follow the re-initializing process (see page C73) after disconnecting the battery, but this isn't the same thing as erasing the codes.
Jeff, Thanks for your response. Sorry but I don't understand the difference between erasing and resetting. Doesn't resetting the ecu erase the error codes? To your knowledge has anyone replicated the test wire and button that is used to pull error codes from the ecu? I've tried Ricambi, Ferrparts, ebay, and one fellow that was parting out a 94 348. Nobody has them and was told that they are discontinued by Ferrari. Any suggestions? I'd know I can start swapping parts to see what shows up on the other side of the engine but would prefer to have the codes. 1/4 cel recently came on. Thanks, John
John; It's two different things. #1: "self diagnosis function". This is where you check for stored error codes in the Motronic ECU's, using the pushbutton and reading the sequence of blinking lights. This is the procedure described in detail in the Workshop Manual, starting on page C78. After reading the codes, THEN you erase them from the memory, again, using the pushbutton. #2: "re-initializing". To quote the Workshop Manual, page C73: "At each battery disconnection or at each operation that causes a current failing of the control unit, all self-learning parameters are erased and it is therefore necessary to reset them before using the vehicle....." So, if you're driving down the road and you get a "check engine" light, you can use the pushbutton to read the error code(s) that have been stored in the Motronic ECU, and interpret them using the chart on page C80, then erase them. If you remove a battery cable, or your battery goes dead, that doesn't trigger an error code, but it does make it necessary to run through the re-initialization process. As far as duplicating the pushbutton, it should be very easy, and I'll try to describe the steps and take a picture or two later this evening. For the moment, are you absolutely SURE that your pushbutton/harness isn't just tucked under the carpeting behind the cover for the Motronic ECU? Can you confirm that you have an open connector (nothing plugged into it) at the harness next to each ECU?
Thanks Jeff, The test wire is not there. I looked at all sides. The wire is hanging on the passengers side of the ECU. There is a receptacle connector at the end of the wire that will accept a three prong plug connector. From the schematics that Eric (and Ricambi) sent to me, it is where the test wire and button should be connected. John
