The manual mode switch is installed on the A/T control device. This switch reports up and downshifts to the TCM (Transmission Control Module). At the same time, the TCM sends signals from the switch to the combination meter via the CAN communication line. Then, the switch is reported on the A/T position indicator.
The Diagnostic Code P1815 OBDII is set when after monitoring the TCM to the Manual Mode Switch, it detects that the switch signal has irregularities by producing an impossible input pattern.
Manual Mode Switch cables or connectors may be faulty.
The Manual Mode Switch (Built-in A/T control device) may be damaged.
The Position Select Switch (Built-in A/T Control Device) may be in bad condition.
Possible solutions of the DTC code P1815
To troubleshoot the DTC P1815 OBDII, try this:
Consult Technical Service Bulletins.
Check electrical components (wiring and connectors) for corrosion, burns, or wear. If you find such conditions, make repairs or replacements.
Use the appropriate tools to verify that the circuit voltages of the Manual Mode Switch and the Position Selector Switch match the specified values. If these tests reveal a short or open circuit, repair if necessary.
Check the condition of the Manual Mode Switch, taking into account the steps outlined by the manufacturer in the service manual. If some damage is found, consider replacing it.