diff --git a/src/sensor/imu/ICM45686.c b/src/sensor/imu/ICM45686.c
index e8a757d8..c9c6194a 100644
--- a/src/sensor/imu/ICM45686.c
+++ b/src/sensor/imu/ICM45686.c
@@ -439,6 +439,148 @@ int icm45_ext_passthrough(bool passthrough)
 	return 0;
 }
 
+int icm45_ext_setup() {
+	int err = 0;
+	err |= ssi_reg_write_byte(SENSOR_INTERFACE_DEV_IMU, ICM45686_IOC_PAD_SCENARIO_AUX_OVRD, 0x17); // AUX1_MODE_OVRD, AUX1 in I2CM Master, AUX1_ENABLE_OVRD, AUX1 enabled
+	sensor_interface_ext_configure(&sensor_ext_icm45686);
+	return err;
+}
+
+int icm45_bank_write(const uint8_t bank, const uint8_t reg, const uint8_t *buf, uint32_t num_bytes)
+{
+	if (num_bytes == 0)
+	{
+		LOG_ERR("Invalid bank write size");
+		return -1;
+	}
+
+	int err = 0;
+	uint8_t ireg_buf[3];
+	ireg_buf[0] = bank;
+	ireg_buf[1] = reg;
+	ireg_buf[2] = buf[0];
+	err |= ssi_burst_write(SENSOR_INTERFACE_DEV_IMU, ICM45686_IREG_ADDR_15_8, ireg_buf, 3);
+	k_usleep(4);
+
+	for (uint32_t i = 1; i < num_bytes; i++)
+	{
+		err |= ssi_reg_write_byte(SENSOR_INTERFACE_DEV_IMU, ICM45686_IREG_DATA, buf[i]);
+		k_usleep(4);
+	}
+
+	return err;
+}
+
+int icm45_bank_write_byte(const uint8_t bank, const uint8_t reg, const uint8_t value)
+{
+	return icm45_bank_write(bank, reg, &value, 1);
+}
+
+int icm45_bank_read(const uint8_t bank, const uint8_t reg, uint8_t *buf, uint32_t num_bytes)
+{
+	if (num_bytes == 0)
+	{
+		LOG_ERR("Invalid bank read size");
+		return -1;
+	}
+
+	int err = 0;
+	uint8_t ireg_buf[2];
+	ireg_buf[0] = bank;
+	ireg_buf[1] = reg;
+	err |= ssi_burst_write(SENSOR_INTERFACE_DEV_IMU, ICM45686_IREG_ADDR_15_8, ireg_buf, 2);
+	k_usleep(4);
+
+	for (uint32_t i = 0; i < num_bytes; i++)
+	{
+		err |= ssi_reg_read_byte(SENSOR_INTERFACE_DEV_IMU, ICM45686_IREG_DATA, &buf[i]);
+		k_usleep(4);
+	}
+	return err;
+}
+
+int icm45_bank_read_byte(const uint8_t bank, const uint8_t reg, uint8_t *value) {
+	return icm45_bank_read(bank, reg, value, 1);
+}
+
+int icm45_ext_write(const uint8_t addr, const uint8_t *buf, uint32_t num_bytes) 
+{
+	if (num_bytes > 6) 
+	{
+		LOG_ERR("Unsupported write");
+		return -1;
+	}
+
+	int err = 0;
+
+	err |= icm45_bank_write(ICM45686_IPREG_TOP1, ICM45686_I2CM_WR_DATA_0, buf, num_bytes);
+	err |= icm45_bank_write_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_COMMAND_0, 0x80 + num_bytes); // Last transaction, channel 0, write num_bytes bytes
+	err |= icm45_bank_write_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_CONTROL, 0x01); // No restarts, fast mode, start transaction
+
+	uint8_t last_status = 0;
+	err |= icm45_bank_read_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_STATUS, &last_status);
+	while (last_status & 0x01) // I2CM busy
+	{
+		err |= icm45_bank_read_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_STATUS, &last_status);
+	}
+
+	if (last_status != 0x02) // Not (just) "done"
+	{
+		LOG_ERR("I2CM error: %02x", last_status);
+		return -1;
+	}
+
+	uint8_t dev_status;
+	err |= icm45_bank_read_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_EXT_DEV_STATUS, &dev_status);
+
+	if (dev_status & 0x01) {
+		// Maybe log the nack?
+		return -1;
+	}
+
+	return err;
+}
+
+int icm45_ext_write_read(const uint8_t addr, const void *write_buf, size_t num_write, void *read_buf, size_t num_read) {
+	if (num_write != 1 || num_read < 1 || num_read > 15)
+	{
+		LOG_ERR("Unsupported write_read");
+		return -1;
+	}
+
+	int err = 0;
+
+	uint8_t dev_profile_data[2] = {((const uint8_t *)write_buf)[0], addr};
+	err |= icm45_bank_write(ICM45686_IPREG_TOP1, ICM45686_DEV_PROFILE_0, dev_profile_data, 2);
+	err |= icm45_bank_write_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_COMMAND_0, 0x90 + num_read); // Last transaction, channel 0, read num_read bytes with register specified
+	err |= icm45_bank_write_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_CONTROL, 0x01); // No restarts, fast mode, start transaction
+
+	uint8_t last_status = 0;
+	err |= icm45_bank_read_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_STATUS, &last_status);
+	while (last_status & 0x01) // I2CM busy
+	{
+		err |= icm45_bank_read_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_STATUS, &last_status);
+	}
+
+	if (last_status != 0x02) // Not (just) "done"
+	{
+		LOG_ERR("I2CM error: %02x", last_status);
+		return -1;
+	}
+
+	uint8_t dev_status;
+	err |= icm45_bank_read_byte(ICM45686_IPREG_TOP1, ICM45686_I2CM_EXT_DEV_STATUS, &dev_status);
+
+	if (dev_status & 0x01) {
+		// Maybe log the nack?
+		return -1;
+	}
+
+	err |= icm45_bank_read(ICM45686_IPREG_TOP1, ICM45686_I2CM_RD_DATA_0, read_buf, num_read);
+
+	return err;
+}
+
 const sensor_imu_t sensor_imu_icm45686 = {
 	*icm45_init,
 	*icm45_shutdown,
@@ -454,7 +596,13 @@ const sensor_imu_t sensor_imu_icm45686 = {
 
 	*icm45_setup_DRDY,
 	*icm45_setup_WOM,
-	
-	*imu_none_ext_setup,
+
+	*icm45_ext_setup,
 	*icm45_ext_passthrough
 };
+
+const sensor_ext_ssi_t sensor_ext_icm45686 = {
+	*icm45_ext_write,
+	*icm45_ext_write_read,
+	15
+};
diff --git a/src/sensor/imu/ICM45686.h b/src/sensor/imu/ICM45686.h
index d4f85cf5..abc4a740 100644
--- a/src/sensor/imu/ICM45686.h
+++ b/src/sensor/imu/ICM45686.h
@@ -53,6 +53,15 @@
 // User Bank IPREG_TOP1
 #define ICM45686_IPREG_TOP1                0xA2 // MSB
 
+#define ICM45686_I2CM_COMMAND_0            0x06
+#define ICM45686_DEV_PROFILE_0             0x0e
+#define ICM45686_DEV_PROFILE_1             0x0f
+#define ICM45686_I2CM_CONTROL              0x16
+#define ICM45686_I2CM_STATUS               0x18
+#define ICM45686_I2CM_EXT_DEV_STATUS       0x1a
+#define ICM45686_I2CM_RD_DATA_0            0x1b
+#define ICM45686_I2CM_WR_DATA_0            0x33
+
 #define ICM45686_SMC_CONTROL_0             0x58
 
 #define ICM45686_SREG_CTRL                 0x67
diff --git a/src/sensor/interface.c b/src/sensor/interface.c
index 59274df5..f3292cd8 100644
--- a/src/sensor/interface.c
+++ b/src/sensor/interface.c
@@ -143,6 +143,9 @@ int ssi_write(enum sensor_interface_dev dev, const uint8_t *buf, uint32_t num_by
 #endif
 	case SENSOR_INTERFACE_SPEC_I2C:
 		return i2c_write_dt(sensor_interface_dev_i2c[dev], buf, num_bytes);
+	case SENSOR_INTERFACE_SPEC_EXT:
+		if (ext_ssi != NULL)
+			return ext_ssi->ext_write(ext_addr, buf, num_bytes);
 	default:
 		return -1;
 	}
@@ -179,9 +182,6 @@ int ssi_read(enum sensor_interface_dev dev, uint8_t *buf, uint32_t num_bytes)
 #endif
 	case SENSOR_INTERFACE_SPEC_I2C:
 		return i2c_read_dt(sensor_interface_dev_i2c[dev], buf, num_bytes);
-	case SENSOR_INTERFACE_SPEC_EXT:
-		if (ext_ssi != NULL)
-			return ext_ssi->ext_write(ext_addr, buf, num_bytes);
 	default:
 		return -1;
 	}