GL1200 Ltd. and SEI Repair -- The ECU (Electronic Control Unit) Box Theory of Operation. Power is supplied to the ECU from the 12 Volt battery source. The ECU using an Internal 5 Volt Regulated Supply (More Guess Work) provides power to the THROTTLE SENSOR, the PBL/PBR Sensors, the Tw, T1, Ns, and GL/GR Sensors. Signals from these Sensors Control the Fuel Injection Timing and Volume, the Operation of the Fuel Pump, by Grounding the FUEL PUMP RELAY #5. They also control Ignition Timing. IF THE BIKE IS RUNNING AT THIS POINT, AND YOU HAVE SOME LED'S THAT ARE LIT, THEN REFER TO THE LED CHART FOR POINTERS AS TO WHAT TO TROUBLE SHOOT. THEN REFER TO THE ARTICLES ON THE VARIOUS SENSORS AND HOW TO CHECK THEM OUT: * T1 Sensor * TW Sensor * NS Sensor * Throttle Sensor * PBL/PBR Sensors * GL/GR Sensors IF THE BIKE IS NOT RUNNING, THEN START WITH TROUBLE SHOOTING THE ECU BOX: --------------------------------------------------------------------------- TROUBLE SHOOTING THE ECU BOX. FIRST: * Check to make sure that the LED's Blink when you turn on the Ignition Switch, and that the Fuel Pump Operates. * If the LED's Blink but the Fuel Pump is not operating, go back and check the section that deals with Relay #5 and the FUEL PUMP itself. * If the LED's are NOT Blinking, then you will have to start by checking for source voltage at the ECU . --------------------------------------------------------------------------- Remove the ECU from its bracket at the back fo the motorcycle. It is located under the Top Box. The ECU is held on by a bracket that has three bolts in it. One on each side near the front of the bracket, and one at the back below the top box. After removing the bracket, CAREFULLY REMOVE the ECU and CAREFULLY DISCONNECT the large connector at the side. BE CAREFUL NOT TO DAMAGE THE LATCHING ASSEMBLY FOR THE CONNECTOR, AND ALSO BE CAREFUL NOT TO DAMAGE THE RUBBER DUST AND MOISTURE SHIELD THAT COVERS IT. Please refer to the Connector Diagram. * KEY ON - KEY ON - KEY ON- KEY ON Check for 12 Volt source at pins # 1 and 19 * KEY OFF - KEY OFF - KEY OFF - KEY OFF With your Voltmeter set in the OHM's position, check for continuity to GROUND at pins # 2, 16, 20, and 34. PINS 3, 24, AND 25 ARE ALSO LISTED AS GROUNDS, BUT THESE ARE THE REGULATED 5 VOLTS GROUNDS, AND RATHER THAN TAKE A CHANCE THAT THEY COULD BE DAMAGED BY THE BATTERY VOLTAGE IN YOUR VOLTMETER, WE WILL PASS THEM BY FOR NOW. If you have the 12 VOLT SOURCE and the CONTINUITY to GROUND that you were looking for, then reconnect the ECU to the connector (CAREFULLY), make sure that it is fully seated in the socket, and turn the key back on, look for the Blinking LED's, and listen to hear the Fuel Pump operate. IF THE LED'S DO NOT BLINK AT THIS POINT, THERE IS A POSSIBILITY (More Guess Work) THAT YOU HAVE AT LEAST LOST THE REGULATED 5 VOLTS SUPPLY INSIDE THE ECU. LET'S CHECK FOR THE REGULATED +5 VOLTS. Find the T1 Sensor. Disconnect the connector on the T1 Sensor. * KEY ON - KEY ON - KEY ON - KEY ON Measure between the two terminals on the T1 Sensor. You should read between 4.75 - 5.25 Volts. IF THERE IS NO +5 VOLT REGULATED SUPPLY, THEN YOU WILL HAVE TO CHECK THE WIRING HARNESS BACK TO THE ECU. IF YOU STILL HAVE NO REGULATED +5 VOLTS, THEN YOU WILL PROBABLY HAVE TO REPLACE THE ECU. IF YOU HAVE THE +5 VOLT SUPPLY, THE LED'S OPERATE, BUT RELAY #5 DOES NOT, THEN YOU HAVE PROBABLY LOST THE FUEL PUMP OPERATING CIRCUIT INSIDE THE ECU. IF THE LED'S AND THE FUEL PUMP RELAY OPERATE, BUT THE FUEL PUMP DOES NOT, THEN YOU WILL PROBABLY HAVE TO REPLACE THE FUEL PUMP. BUT DON'T RUSH OUT AND BUY A NEW FUEL PUMP YET. CHECK THE SECTION THAT DEALS WITH THE FUEL PUMP FIRST. IF THE LED'S AND THE FUEL PUMP OPERATE, THEN SEE IF THE MOTORCYCLE WILL NOW START. IF IT STARTS, AND SEEMS TO RUN PROPERLY, THEN PUT IT BACK TOGETHER. IF IT RUNS, BUT POORLY, THEN CHECK THE LED INDICATORS AND THE REFERENCE CHART FOR POINTERS TO BEGIN TROUBLE SHOOTING. IF YOUR LED'S DO NOT OPERATE, THE FUEL PUMP DOES NOT OPERATE, THERE IS NO +5 VOLT REGULATED SUPPLY AND THE BIKE WILL NOT START AT THIS POINT THEN YOU PROBABLY HAVE A BAD ECU (Electronic Control Unit) The last time that I checked, this unit cost $ 1500.00 In Order, if I was reasonably convinced that the ECU had gone bad, I would: * CALL American Honda, and see if they, or anyone that they knew would/could rebuild the ECU. * Take it to a good electronics man, and let them see if the problem was only the regulated 5 volts circuit first. Take the Wiring Diagram and the Connector Diagram with you. * Search for a USED ECU at whatever sources were available to me. * BUY a brand new unit from you local Honda Dealer. --------------------------------------------------------------------------- Continue | Table of Contents