diff --git a/Core/Inc/AMS_CAN.h b/Core/Inc/AMS_CAN.h
index 31c42a4..5bc3e50 100644
--- a/Core/Inc/AMS_CAN.h
+++ b/Core/Inc/AMS_CAN.h
@@ -14,6 +14,8 @@
 #include "stm32f4xx_hal_can.h"
 #include "stm32f4xx_hal_def.h"
 
+#include <stdint.h>
+
 #define CAN_ID_SLAVE_ERROR 0x001
 #define CAN_ID_AMS_SLAVE_HEARTBEAT_BASE 0x600
 #define CAN_HEARTBEAT_TX_TIMEOUT 5 /* ms */
@@ -24,9 +26,18 @@ void ams_can_handle_ams_msg(CAN_RxHeaderTypeDef* header, uint8_t* data);
 void ams_can_handle_car_msg(CAN_RxHeaderTypeDef* header, uint8_t* data);
 
 void ams_can_send_heartbeat();
-void ams_can_send_error(AMS_ErrorCode error_code);
+/**
+ * @brief Send an AMS Error via CAN.
+ *
+ * @param error_code The kind of error
+ * @param transmission_timeout How long to wait for the transmission to complete
+ * after starting it (in ms). Set to 0 for no wait.
+ */
+void ams_can_send_error(AMS_ErrorCode error_code,
+                        uint32_t transmission_timeout);
 
-HAL_StatusTypeDef ams_can_wait_for_free_mailbox(CAN_HandleTypeDef* handle,
-                                                uint32_t timeout);
+HAL_StatusTypeDef ams_can_wait_for_free_mailboxes(CAN_HandleTypeDef* handle,
+                                                  int num_mailboxes,
+                                                  uint32_t timeout);
 
 #endif /* INC_AMS_CAN_H_ */
diff --git a/Core/Inc/BQ_Abstraction_Layer.h b/Core/Inc/BQ_Abstraction_Layer.h
index 366c2dc..e286246 100644
--- a/Core/Inc/BQ_Abstraction_Layer.h
+++ b/Core/Inc/BQ_Abstraction_Layer.h
@@ -20,6 +20,7 @@
 #define CELL_UV_THRESHOLD 34100 // 2.6V
 
 extern uint16_t cell_voltages[N_CELLS];
+extern uint16_t max_voltage, min_voltage;
 
 typedef enum { BQ_OFF, BQ_RDY, BQ_STDBY, BQ_INIT_PHASE, BQ_ERROR } BQ_Status;
 extern BQ_Status bq_status;
diff --git a/Core/Inc/main.h b/Core/Inc/main.h
index 0760271..88b5bfb 100644
--- a/Core/Inc/main.h
+++ b/Core/Inc/main.h
@@ -40,7 +40,9 @@ typedef enum {
   AMS_ERROR_UV,
   AMS_ERROR_OV,
   AMS_ERROR_UT,
-  AMS_ERROR_OT
+  AMS_ERROR_OT,
+  AMS_ERROR_BQ,
+  AMS_ERROR_TMP144
 } AMS_ErrorCode;
 /* USER CODE END ET */
 
@@ -51,7 +53,12 @@ extern uint8_t slave_id;
 
 /* Exported macro ------------------------------------------------------------*/
 /* USER CODE BEGIN EM */
-#define MAIN_LOOP_PERIOD 100 /* ms */
+#define MAIN_LOOP_PERIOD 100   /* ms */
+#define AMS_ERROR_TX_TIMEOUT 2 /* ms */
+#define THRESH_UV 32768        /* 2.5V */
+#define THRESH_OV 55050        /* 4.2V */
+#define THRESH_UT 0            /* 0C */
+#define THRESH_OT 880          /* 55C */
 /* USER CODE END EM */
 
 void HAL_TIM_MspPostInit(TIM_HandleTypeDef* htim);
@@ -61,6 +68,7 @@ void Error_Handler(void);
 
 /* USER CODE BEGIN EFP */
 void update_status_leds();
+void check_error_conditions();
 void delay_period();
 /* USER CODE END EFP */
 
diff --git a/Core/Src/AMS_CAN.c b/Core/Src/AMS_CAN.c
index 28f9a77..8a8ce16 100644
--- a/Core/Src/AMS_CAN.c
+++ b/Core/Src/AMS_CAN.c
@@ -16,6 +16,8 @@
 #include "stm32f4xx_hal.h"
 #include "stm32f4xx_hal_can.h"
 
+#include <stdint.h>
+
 static CAN_HandleTypeDef* handle_ams;
 static CAN_HandleTypeDef* handle_car;
 
@@ -127,7 +129,8 @@ void ams_can_send_heartbeat() {
   }
 }
 
-void ams_can_send_error(AMS_ErrorCode error_code) {
+void ams_can_send_error(AMS_ErrorCode error_code,
+                        uint32_t transmission_timeout) {
   static CAN_TxHeaderTypeDef header;
   header.IDE = CAN_ID_STD;
   header.DLC = 8;
@@ -143,13 +146,15 @@ void ams_can_send_error(AMS_ErrorCode error_code) {
                          CAN_TX_MAILBOX0 | CAN_TX_MAILBOX1 | CAN_TX_MAILBOX2);
   uint32_t mailbox;
   HAL_CAN_AddTxMessage(handle_ams, &header, data, &mailbox);
+  ams_can_wait_for_free_mailboxes(handle_ams, 3, transmission_timeout);
 }
 
-HAL_StatusTypeDef ams_can_wait_for_free_mailbox(CAN_HandleTypeDef* handle,
-                                                uint32_t timeout) {
+HAL_StatusTypeDef ams_can_wait_for_free_mailboxes(CAN_HandleTypeDef* handle,
+                                                  int num_mailboxes,
+                                                  uint32_t timeout) {
   uint32_t end = HAL_GetTick() + timeout;
   while (HAL_GetTick() < end) {
-    if (HAL_CAN_GetTxMailboxesFreeLevel(handle) > 0) {
+    if (HAL_CAN_GetTxMailboxesFreeLevel(handle) >= num_mailboxes) {
       return HAL_OK;
     }
   }
diff --git a/Core/Src/BQ_Abstraction_Layer.c b/Core/Src/BQ_Abstraction_Layer.c
index 1c686aa..5ee6ade 100644
--- a/Core/Src/BQ_Abstraction_Layer.c
+++ b/Core/Src/BQ_Abstraction_Layer.c
@@ -16,6 +16,7 @@
 #include <string.h>
 
 uint16_t cell_voltages[N_CELLS];
+uint16_t max_voltage, min_voltage;
 
 BQ_Status bq_status;
 BQ_Error_Description bq_error;
@@ -82,11 +83,20 @@ void afe_measure() {
   lastmeasurementtime = HAL_GetTick();
 
   if (retval == BQ_COMM_OK) {
+    uint16_t max = 0;
+    uint16_t min = 0xFFFF;
     for (int n = 0; n < N_CELLS; n++) {
-      cell_voltages[N_CELLS - 1 - n] =
-          (uint16_t)(cellvoltagebuffer[2 * n] << 8) +
-          (uint16_t)cellvoltagebuffer[2 * n + 1];
+      uint16_t v = cellvoltagebuffer[2 * n] << 8 | cellvoltagebuffer[2 * n + 1];
+      cell_voltages[N_CELLS - 1 - n] = v;
+      if (v > max) {
+        max = v;
+      }
+      if (v < min) {
+        min = v;
+      }
     }
+    max_voltage = max;
+    min_voltage = min;
   } else if (retval == BQ_COMM_ERR_HAL) {
     bq_set_error_with_loc(BQ_COMM_ERR_HAL, BQ_ERROR_LOC_MEASURE);
   } else if (retval == BQ_COMM_ERR_CRC) {
diff --git a/Core/Src/main.c b/Core/Src/main.c
index 3c8d85d..a572064 100644
--- a/Core/Src/main.c
+++ b/Core/Src/main.c
@@ -21,10 +21,12 @@
 
 /* Private includes ----------------------------------------------------------*/
 /* USER CODE BEGIN Includes */
+#include "AMS_CAN.h"
 #include "BQ_Abstraction_Layer.h"
 #include "EEPROM.h"
 #include "FanControl.h"
 #include "TMP144.h"
+#include "common_defs.h"
 
 #include "stm32f4xx_hal.h"
 #include "stm32f4xx_hal_gpio.h"
@@ -94,6 +96,29 @@ void update_status_leds() {
   }
 }
 
+void check_error_conditions() {
+  if (bq_status != BQ_RDY) {
+    ams_can_send_error(AMS_ERROR_BQ, AMS_ERROR_TX_TIMEOUT);
+  }
+  tmp144_check_timeouts();
+  if (tmp144_bus_busbar.state == TMP144_ERROR ||
+      tmp144_bus_other.state == TMP144_ERROR) {
+    ams_can_send_error(AMS_ERROR_TMP144, AMS_ERROR_TX_TIMEOUT);
+  }
+  if (min_voltage < THRESH_UV) {
+    ams_can_send_error(AMS_ERROR_UV, AMS_ERROR_TX_TIMEOUT);
+  }
+  if (max_voltage > THRESH_OV) {
+    ams_can_send_error(AMS_ERROR_OV, AMS_ERROR_TX_TIMEOUT);
+  }
+  if (min_temperature < THRESH_UT) {
+    ams_can_send_error(AMS_ERROR_UT, AMS_ERROR_TX_TIMEOUT);
+  }
+  if (max_temperature > THRESH_OT) {
+    ams_can_send_error(AMS_ERROR_OT, AMS_ERROR_TX_TIMEOUT);
+  }
+}
+
 void delay_period() {
   static uint32_t last_it = 0;
   uint32_t now = HAL_GetTick();
@@ -161,8 +186,9 @@ int main(void) {
     /* USER CODE BEGIN 3 */
     update_status_leds();
     afe_measure();
+    tmp144_read_temps();
+    check_error_conditions();
     delay_period();
-    fan_ctrl_set_power((HAL_GetTick() / 100) % 100);
   }
   /* USER CODE END 3 */
 }