Slow Down light again

Since you cannot swap side to side, since there is only one "slow down" light, you have only a couple options. 90% of the time it is simply a bad cat ecu. You could buy one, and install it on either the left or right side and see what happens...if the light still comes up, then swap sides. But, it is also possible, (though less likely) it is the thermocouple.

Here is the Cat ECU: http://www.ricambiamerica.com/product_info.php?products_id=208023

Here is the parts diagram and locations: http://www.ricambiamerica.com/parts_catalogs.php?M=FE&P=&V=diag&I=317

 

Recently the CHECK ENGINE and SLOW DOWN lights flashed on my 2000 550 Maranello while I was out for a short drive. Car was only on road for about 5-10 minutes before lights came on. Waited a day for car to go to room temp., then restarted. Immediately see CHECK ENGINE/SLOW DOWN flashing light and reduced power. Right cylinder bank does not appear to be firing (no exhaust out of right/passenger side pipes) and the car has reduced power. Contacted the dealer and he suggested I flat-bed it to his shop. After spending some time reading forums, I tried several basic diagnostics to avoid having it flat-bedded (dealer is ~70 miles away). So far I've been unable to find the problem source. Here's what I tried:

1. The battery was last replaced over 5 years ago. So I purchased Schumacher BT-100 battery tester to determine battery strength (one forum suggested that a voltage drop while starting could lead to unreliable ECU behavior). After disconnecting battery from car and testing, it showed borderline weak. So I purchased and installed a new Bosch battery and restarted the car. Same result, no ignition on right bank.

2. Per my dealer's suggestion, I checked the vintage of the catalytic converter control units. Both have a green front facing the connectors (later versions). I tried swapping the catalytic control units (left on right bank, and right on left bank), then restarted the engine. Same result, no ignition on right bank.

3. With the engine off and cold, I disconnected both catalytic thermocouples from the control units and measured their resistances. At room temperature the resistances were virtually the same. I then reconnected and restarted, let the engine run for about 5-10 minutes while looking underneath at the right catalytic converter to see if it appeared hot or had signs of heat. It appeared normal, no color change or excessive heat.

4. Purchased Actron CP9125 code scanner and read error code P1445 pending. Can erase codes, but still no firing of right side cylinders.

At this point are there any other simple tests I can try before surrendering to the flat bed? How difficult are the thermocouples to swap (do I need special tool)? Car has Tubi exhaust system for several years, ~6000 miles, and dealer corrected CHECK ENGINE light last year by replacing faulty secondary air pump electical relay.

Any assistance is greatly appreciated!
Thanks in advance.

 

No right side, reduced power and slow-downlight.

Normally slowdown comes with fuel being burned in catalytic converter instead of cylinder. That rules out things like battery or other DIY stuff. Ignition is failing on right bank. If FI was failing, there wouldn't be raw fuel in the cat to burn.

I liked the "waited a day for engine to cool" bit. Shows character to have sense of humor in an adverse situation.

Let us know the outcome.

 

I haven't ever changed them on a 550, but on my 348 they are way easy to change. They are just screwed into the cats. So all you have to do is unscrew them from the cat and unplug it from the cat ecu. Then swap them from side to side to see if the ecu shuts down the left side.

While your at it, I would have a look to make sure the connectors aren't dirty, and that you don't have any busted wires.

 

My resolution was to take car to dealer, where they "checked fuses and discovered no power to fuse for RS FUEL PUMP. Found bad RELAY and replaced it, connected SD2 and cleared errors and reset parameters."