Connecting to Custom Service/Characteristic of BLE peripheral with nRF52 acting as central.

Question

I am currently connected to a BLE peripheral with the nRF52 acting as the central. I am able to scan using the device's name and connect. I created a custom file to handle the central functions including adding the custom UUID and starting the discovery. This done here

uint32_t ble_obd_c_init(ble_obd_c_t * p_obd_service_client, ble_obd_c_init_t * p_ble_obd_c_init)
{
    uint32_t      err_code;
    ble_uuid_t    obd_uuid;
    // TODO for V Link
    ble_uuid128_t obd_base_uuid = OBD_BASE_UUID;
    obd_uuid.uuid = BLE_UUID_OBD_SERVICE;
    obd_uuid.type = BLE_UUID_TYPE_VENDOR_BEGIN;

    VERIFY_PARAM_NOT_NULL(p_obd_service_client);
    VERIFY_PARAM_NOT_NULL(p_ble_obd_c_init);

    err_code = sd_ble_uuid_vs_add(&obd_base_uuid, &obd_uuid.type);
    VERIFY_SUCCESS(err_code);

    p_obd_service_client->conn_handle                    = BLE_CONN_HANDLE_INVALID;
    p_obd_service_client->evt_handler                    = p_ble_obd_c_init->evt_handler;
    p_obd_service_client->error_handler                  = p_ble_obd_c_init->error_handler;
    p_obd_service_client->obd_service_char.handle_value  = BLE_GATT_HANDLE_INVALID;
    p_obd_service_client->p_gatt_queue                   = p_ble_obd_c_init->p_gatt_queue;
    p_obd_service_client->uuid_type                      = BLE_UUID_TYPE_VENDOR_BEGIN;

    return ble_db_discovery_evt_register(&obd_uuid);
}

The discovery runs smoothly and finds the Service. The issue is that the characteristic is not there, so I am unable to read and write to the device. This is where I try and find the characteristic. The uuid type is returning as 4, but I thought there was only 0, 1, and 2 (I set it to 2, the BLE_UUID_TYPE_VENDOR_BEGIN).

void ble_obd_c_on_db_disc_evt(ble_obd_c_t * p_obd_service_client, ble_db_discovery_evt_t * p_evt)
{
    memset(&obd_c_evt,0,sizeof(ble_obd_c_evt_t));

    ble_gatt_db_char_t * p_chars = p_evt->params.discovered_db.charateristics;

    // Check if the OBD was discovered.
    if (    (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE)
        &&  (p_evt->params.discovered_db.srv_uuid.uuid == BLE_UUID_OBD_SERVICE)
        &&  (p_evt->params.discovered_db.srv_uuid.type == p_obd_service_client->uuid_type))
    {
        for (uint32_t i = 0; i < p_evt->params.discovered_db.char_count; i++)
        {
            switch (p_chars[i].characteristic.uuid.uuid)
            {
                case BLE_UUID_OBD_CHARACTERISTIC:
                    // Found OBD characteristic inside the OBD Service.
                    p_obd_service_client->obd_service_char = p_chars[i].characteristic;
                    NRF_LOG_INFO("Discovered characteristic handle: %i", p_chars[i].characteristic.handle_value);
                    break;

                default:
                    break;
            }
        }
        if (p_obd_service_client->evt_handler != NULL)
        {
            obd_c_evt.conn_handle = p_evt->conn_handle;
            obd_c_evt.evt_type    = BLE_OBD_C_EVT_DISCOVERY_COMPLETE;
            p_obd_service_client->evt_handler(p_obd_service_client, &obd_c_evt);
        }
    }
}

These are my defines for the custom service/characteristics of the OBD device

#define OBD_BASE_UUID {{0xF2, 0xC3, 0xF0, 0xAE, 0xA9, 0xFA, 0x15, 0x8C, 0x9D, 0x49, 0xAE, 0x73, 0x71, 0x0A, 0x81, 0xE7}}

#define BLE_UUID_OBD_SERVICE 0x0A71 //< The UUID of the OBD Service.
#define BLE_UUID_OBD_CHARACTERISTIC 0xD6C9 // < The UUID of the RX and TX Characteristic.

I attached an image of the service/characteristic from nRF52 connect.

I have another OBD device that uses 16 bit UUIDS and was able to do this easily, but since these use 128 bit UUIDs, I am running into some issues.

I have attached my wireshark capture from when I establish a connection, search for the service and then search for the characteristic for a working device and the non-working one. The LE Link Capture is working while the VLINK does not.

3225.VLINK Capture from connecting.pcapng 5381.LE LINK Capture from connecting.pcapng VLINK to iOS Capture from connecting.pcapng