On my 94 348, the cat ecu's have two plugs. One larger than the other. On my car, the larger ones were unplugged (both sides, thanks dealer!). What does the smaller plug do? Is there any issue with unplugging it too? I've read that many people unplug the larger plugs because of modified exhaust systems, etc. (mine is stock) to prevent the 'slow down' lights from coming on. I've searched the forums but have found no info on the difference / impact of having both plugs disconnected versus one or both connected. J
On these cat ECU, the larger plug is the connection to the Motronic engine ECU, the smaller one is the connection to the thermocouple which is bolted in the cat. If the larger plug is disconnected there is no difference whether the smaller is connected or not. The cat ECU is no more switched on anyway. In your case, if you have stock exhaust including the cats, I would strongly recommand you to have these plugs reconnected (and the cat ECU repaired if needed) in order to allow the cat temperature monitoring by engine ECU and allow the "slow down" lights to come on if necessary (cat overheated!).
Check to see if your SLOW DOWN lights and your Check Engine Lights 1-4 & 5-8 illuminate when you turn your iginition key to Position II (run, not start) with engine off. When people start disconnecting safety circuits, you enter that grey zone where they may be removing other "useful" items such as CEL bulbs or SLOW DOWN bulbs, etc. Of course, in your case you probably won't see the SLOW DOWN lights since it appears that your exhaust ecus are disconnected...but might as well check everything.
My concern would be why did the dealer disconnect them in the first place? Plug them in, drive your car for a bit and pull your engine codes (Canadian models also have the button beside the main ECU's to pull engine codes).
I took everyone's advice here and reconnected the cat ecus. The slow down 5/8 light came on almost immediate, so I swapped the cat ecus and then immediately thereafter the slow down 1/4 light came on. I switched the ecus back to be sure, and sure enough, the slow down 5/8 light came back on. The car wasn't even warm. I am very concerned as to why the dealer (a real Ferrari dealer in Montreal) would disconnect both cat ecus. When I bought the car from them 2 years ago, it came with a 4 month warranty. The slow down lights both went on within a month of me buying the car. It appears that instead of opting to fix the problem correctly, they decided to simply disconnect BOTH cat ecus putting my safety at risk and putting their bottom line first. Does anyone have a recommendation on my next steps (besides replacing the one faulty cat ecu)? Thanks all. JD
Tasteless! If they both have the black potting material I would suggest you replace them both so you can trust the warning lights. Dave
