From Gemini:
Since your check engine light (CEL) works during diagnostics but fails to illuminate during the normal key-on sequence, it is highly likely that your ECM is not receiving power or is failing its internal boot-up check. This prevents the fuel pump from priming correctly or the ignition system from maintaining a run state, causing the start-and-stall symptom.
Given you just completed cam chest work, focus on these specific areas:
1. Crankshaft Position Sensor (CKP) Connection
During cam chest work, it is common to move or disconnect the CKP sensor (located near the front of the engine case).
If the ECM does not see a valid signal from the CKP immediately after starting, it will shut down the engine. Ensure the connector is fully seated and the wires weren't pinched when you reinstalled the timing cover.
2. Pins and Connectors (The "Wiggle" Test)
Bent Pins: If you disconnected the ECM or main harness, check for bent pins in the ECM connector. These are notoriously easy to damage.
Corrosion/Fretting: Look for dark spots on terminals that might indicate terminal fretting, which causes intermittent power loss.
3. System Ground and Power
Main Ground: Re-verify the battery ground connection to the frame. A weak ground can allow enough power for dash lights but fail under the load of the ECM and ignition.
System Relay: You mentioned the relay is "good," but verify that it clicks when the run/stop switch is flipped. If it doesn't click, the ECM isn't sending the "turn on" signal, or the ignition switch itself is failing to provide the trigger voltage.
4. Diagnostic Code Check
Even if the light doesn't come on, use the odometer reset button to enter diagnostic mode:
Look specifically for "no response" or "no comm" errors in the P (ECM) or S (TSM/TSSM) sections.
If the speedometer says "no response" for the ECM, the module is definitely not powering up.
These guides explain how to troubleshoot ECM power, ignition switch faults, and diagnostic code checks to resolve your motorcycle's start-and-stall issue