viewsouth, here is the procedure that my Toyota dealer gave me (I'm having the same issue with my '07 Tundra DC with security system). These instructions are the same as those that I got off of one of the Toyota Solutions forums. I've not been able to successfully execute them, but am going to try again tonight. I think you really need to be within the time allowances on all the steps... Let me know if this works for you. REGISTER RECOGNITION CODE (USING SWITCH OPERATION) (a) The following conditions must be met. • No key in the ignition key cylinder. • The driver side door is open (the other doors are closed). • The driver side door is unlocked. (b) Insert and remove the key into / from the ignition key cylinder twice (Insert → Remove → Insert → Remove) within 5 seconds. HINT: The procedure should end with the key removed. (c) Perform the following operations within 40 seconds. (1) Close and open the driver side door twice (Close → Open → Close → Open). HINT: The procedure should end with the door open. (2) Insert and remove the key into / from the ignition key cylinder (Insert → Remove). HINT: The procedure should end with the key removed. (3) Close and open the driver side door twice (Close → Open → Close → Open). HINT: The procedure should end with the door open. (4) Insert the key into the ignition key cylinder and close all doors. (d) Perform the following operations within 40 seconds. (1) Turn the ignition switch from ON to OFF at approximately 1 second intervals. Operate the ignition switch according to the number of times shown in Figure on left below. HINT: If the number of ignition switch ON - OFF operations is 0, 4, 6 or more, there will be no response (the power door lock and unlock operation) to show which mode has been selected. (2) Remove the key from the ignition key cylinder. (e) Check the response of the selected mode within 5 seconds. (Refer to Figure on right below) NOTICE: After the system has been set to the prohibition mode, enter the confirmation mode and check that the number of registered keys is 0. HINT: • In the confirmation mode, LOCK-UNLOCK operation will occur once for each recognition code that has been registered. For example, if 2 recognition codes have been registered, LOCK-UNLOCK operation will occur twice. • In the confirmation mode, if no recognition codes have been registered, LOCK-UNLOCK operation will occur 5 times. • If confirmation mode or prohibition mode is selected, the operation ends after the response to the selected mode completes. (f) If add mode or rewrite mode is selected, perform the following procedures. (1) Press a single switch (LOCK or UNLOCK) within 5 seconds. (2) After completing the above step, check the response to the registration completion within 3 seconds. HINT: • If the LOCK-UNLOCK operation occurs twice, the registration of the recognition code has failed. Perform registration procedures again from the beginning. • If registering another transmitter, repeat the procedures after the response to the selected mode confirmation. All 4 recognition codes can be registered consecutively. (g) Perform either of the following to complete the registration of the recognition codes: • Open the door. • Insert the key into the ignition key cylinder.