Checking Honda Circuits
This bulletin provides tips from Honda that applies to all models when troubleshooting DTCs for a solenoid or motor power supply circuit failure. Even though the control unit activates these components, the power supply may come from a dedicated circuit and its own separate fuse. This is most commonly overlooked when troubleshooting transmission or VTEC solenoid circuits. If the troubleshooting leads you to replace a control unit, make sure you understand and inspect all of the power supplies to that control unit first.
There are at least four power supply circuits connected to the transmission control module. Generally, solenoid or motor power supply circuits will have a label of B+, VB or IG1 to indicate a power supply circuit, and SOL or MOTOR is referring to the component being supplied power, but the label itself may not always read this way. Be sure to review and verify any power supply circuits going to the control unit first. Checking for blown, missing or misplaced fuses can be a quick first step that can prevent unnecessary troubleshooting.