diff --git a/firmware/can.cpp b/firmware/can.cpp
index 872066b..fdff4bd 100644
--- a/firmware/can.cpp
+++ b/firmware/can.cpp
@@ -37,6 +37,11 @@ static void SendAck()
     canTransmitTimeout(&CAND1, CAN_ANY_MAILBOX, &frame, TIME_INFINITE);
 }
 
+// Start in Unknown state. If no CAN message is ever received, we operate
+// on internal battery sense etc.
+static HeaterAllow heaterAllow = HeaterAllow::Unknown;
+static float remoteBatteryVoltage = 0;
+
 static THD_WORKING_AREA(waCanRxThread, 256);
 void CanRxThread(void*)
 {
@@ -60,13 +65,27 @@ void CanRxThread(void*)
         if (frame.DLC == 2 && frame.EID == WB_MGS_ECU_STATUS) {
             // This is status from ECU - battery voltage and heater enable signal
 
+            // data1 contains heater enable bit
+            if ((frame.data8[1] & 0x1) == 0x1)
+            {
+                heaterAllow = HeaterAllow::Allowed;
+            }
+            else
+            {
+                heaterAllow = HeaterAllow::NotAllowed;
+            }
+
             // data0 contains battery voltage in tenths of a volt
             float vbatt = frame.data8[0] * 0.1f;
-            SetBatteryVoltage(vbatt);
-
-            // data1 contains heater enable bit
-            bool heaterAllowed = (frame.data8[1] & 0x1) == 0x1;
-            SetHeaterAllowed(heaterAllowed);
+            if (vbatt < 5)
+            {
+                // provided vbatt is bogus, default to 14v nominal
+                remoteBatteryVoltage = 14;
+            }
+            else
+            {
+                remoteBatteryVoltage = vbatt;
+            }
         }
         // If it's a bootloader entry request, reboot to the bootloader!
         else if (frame.DLC == 0 && frame.EID == WB_BL_ENTER)
@@ -90,6 +109,16 @@ void CanRxThread(void*)
     }
 }
 
+HeaterAllow GetHeaterAllowed()
+{
+    return heaterAllow;
+}
+
+float GetRemoteBatteryVoltage()
+{
+    return remoteBatteryVoltage;
+}
+
 void InitCan()
 {
     configuration = GetConfiguration();
diff --git a/firmware/can.h b/firmware/can.h
index 25bd081..c0d67a5 100644
--- a/firmware/can.h
+++ b/firmware/can.h
@@ -5,3 +5,13 @@
 void InitCan();
 void SendCanData(float lambda, uint16_t measuredResistance);
 void SendRusefiFormat(uint8_t idx);
+
+enum class HeaterAllow {
+    Unknown,
+    Allowed,
+    NotAllowed,
+};
+
+HeaterAllow GetHeaterAllowed();
+
+float GetRemoteBatteryVoltage();
diff --git a/firmware/heater_control.cpp b/firmware/heater_control.cpp
index 57a7d19..5be58f4 100644
--- a/firmware/heater_control.cpp
+++ b/firmware/heater_control.cpp
@@ -8,6 +8,7 @@
 #include "pwm.h"
 #include "sampling.h"
 #include "pid.h"
+#include "can.h"
 
 using namespace wbo;
 
@@ -25,10 +26,12 @@ enum class HeaterState
 constexpr int preheatTimeCounter = HEATER_PREHEAT_TIME / HEATER_CONTROL_PERIOD;
 static int timeCounter = preheatTimeCounter;
 static float rampVoltage = 0;
-static bool heaterAllowed = false;
 
-static HeaterState GetNextState(HeaterState state, float sensorEsr)
+static HeaterState GetNextState(HeaterState state, HeaterAllow heaterAllowState, float batteryVoltage, float sensorEsr)
 {
+    // TODO: smarter state machine to use internal vbatt when CAN not connected
+    bool heaterAllowed = heaterAllowState == HeaterAllow::Allowed;
+
     if (!heaterAllowed)
     {
         // ECU hasn't allowed preheat yet, reset timer, and force preheat state
@@ -130,8 +133,6 @@ static float GetVoltageForState(HeaterState state, float heaterEsr)
 
 static HeaterState state = HeaterState::Preheat;
 
-// Nominal battery voltage (running engine) is 14v
-static float batteryVoltage = 14;
 
 static THD_WORKING_AREA(waHeaterThread, 256);
 static void HeaterThread(void*)
@@ -145,8 +146,16 @@ static void HeaterThread(void*)
         // Read sensor state
         float heaterEsr = GetSensorInternalResistance();
 
+        auto heaterAllowState = GetHeaterAllowed();
+
+        // If we haven't heard from rusEFI, use the internally sensed 
+        // battery voltage instead of voltage over CAN.
+        float batteryVoltage = heaterAllowState == HeaterAllow::Unknown
+                                    ? GetInternalBatteryVoltage()
+                                    : GetRemoteBatteryVoltage();
+
         // Run the state machine
-        state = GetNextState(state, heaterEsr);
+        state = GetNextState(state, heaterAllowState, batteryVoltage, heaterEsr);
         float heaterVoltage = GetVoltageForState(state, heaterEsr);
 
         // Limit to 11 volts
@@ -187,24 +196,6 @@ bool IsRunningClosedLoop()
     return state == HeaterState::ClosedLoop;
 }
 
-void SetBatteryVoltage(float vbatt)
-{
-    if (vbatt < 5)
-    {
-        // provided vbatt is bogus, default to 14v nominal
-        batteryVoltage = 14;
-    }
-    else
-    {
-        batteryVoltage = vbatt;
-    }
-}
-
-void SetHeaterAllowed(bool allowed)
-{
-    heaterAllowed = allowed;
-}
-
 float GetHeaterDuty()
 {
     return heaterPwm.GetLastDuty();
diff --git a/firmware/heater_control.h b/firmware/heater_control.h
index 7f4e680..b150095 100644
--- a/firmware/heater_control.h
+++ b/firmware/heater_control.h
@@ -4,6 +4,4 @@
 
 void StartHeaterControl();
 bool IsRunningClosedLoop();
-void SetBatteryVoltage(float vbatt);
-void SetHeaterAllowed(bool allowed);
 float GetHeaterDuty();