Join Date: Apr 2005
Location: Guilford, CT, USA
The Clymer schematic (as far as I can read it) indicates that the left and right fan motors are switched by a fan relay. Power from the relay to the fans goes thru fuses F9 and F10 in Fuse box 3. The fan relay also has a circuit that goes thru fuse F1 in Fuse box 1 that connects with the ignition coils on one branch and the Motronic on another branch (I think; the two-page schematic shows a line that is green/black up to the right margin on the left page, but no corresponding line from the left margin of the right page. Clearly an error in the schematic. Another green/black line connects the Motronic relay to the Motronic control unit at pin 1, so I assume the fan relay circuit is a branch.) So, one possibility would be that the fan relay is triggered by the motronic, the circuit is closed to the left and right fan motors, but at the same time there is a disruption in the circuit that connects the fan relay and the ignition coils.
The coolant temperature sensor (AKA engine temp sensor) has a direct connection to the throttle potentiometer, and both the coolant temp sensor and the throttle potentiometer connect to the motronic. I'm guessing that the motronic sends a signal to the fan relay when the coolant temp sensor output indicates "too hot;" this signal turns on the fans. At the same time the motronic shuts down the engine, either through the fuel pump relay (shutting of the fuel pump) or through the ignition coils (which have direct connections to the motronic).
Question for the gurus: is there a fail-safe circuit on the LT that shuts the engine down if the temp goes above a predetermined point? If so, maybe that is being activated by erroneous info from the coolant temp sensor?
Otherwise you may be looking for a new motronic, unfortunately.
Added: Just re-read your last post. The tech said no spark when the engine shut down. Definitely coil related. I'd think about checking that fan relay before digging out the motronic.
'99 Canyon Red K1200 LT - Buddah Bike
Last edited by was; Aug 10th, 2007 at 3:30 pm.