diff --git a/lambda-test/adc-test.c b/lambda-test/adc-test.c
index 396ca3f..e8951b8 100644
--- a/lambda-test/adc-test.c
+++ b/lambda-test/adc-test.c
@@ -21,8 +21,7 @@
 	// AVCC is set as AREF
 	assertTrue(bit_is_set(ADMUX, REFS0));
 	// digital inputs are disabled
-	uint8_t adcPorts = (1 << ADC_TEMPI) | (1 << ADC_TEMPO) | (1 << ADC_LAMBDA);
-	assertTrue((DIDR0 & adcPorts) == adcPorts);
+	assertTrue(DIDR0 == 0b00111111);
 	// ADC clock prescaler/8
 	uint8_t prescalerBy8 = (1 << ADPS1) | (1 << ADPS0);
 	assertTrue((ADCSRA & prescalerBy8) == prescalerBy8);
diff --git a/lambda-test/alert-test.c b/lambda-test/alert-test.c
index ed0f9e7..89078bb 100644
--- a/lambda-test/alert-test.c
+++ b/lambda-test/alert-test.c
@@ -22,7 +22,7 @@
 	oscCount = 0;
 
 	// alert with two beeps with a length of 2 and tone 31
-	alert(2, 2, 31, "a", "b");
+	alert(2, 2, 31, "a", "b", false);
 	oscillateBeep();
 	oscillateBeep();
 
@@ -91,7 +91,7 @@
 	beepLength = 0;
 	oscCount = 0;
 
-	alert(1, 2, 31, "a", "b");
+	alert(1, 2, 31, "a", "b", false);
 
 	assertTrue(beepCount == 1);
 	assertTrue(beepLength == 2);
@@ -111,7 +111,7 @@
 	beepLength = 0;
 	oscCount = 0;
 
-	alert(1, 2, 31, "a", "b");
+	alert(1, 2, 31, "a", "b", true);
 
 	assertTrue(beepCount == 1);
 	assertTrue(beepLength == 2);
@@ -124,6 +124,14 @@
 	assertTrue(beepCount == 0);
 	assertTrue(oscCount == 0);
 	assertTrue(bit_is_clear(TCCR1A, COM1A0));
+	assertTrue(isAlertActive());
+
+	alert(1, 2, 31, "a", "b", false);
+
+	assertTrue(isAlertActive());
+
+	cancelAlert();
+
 	assertFalse(isAlertActive());
 
 	return true;
diff --git a/lambda-test/display-test.c b/lambda-test/display-test.c
index f026ea0..fe4c77c 100644
--- a/lambda-test/display-test.c
+++ b/lambda-test/display-test.c
@@ -49,7 +49,7 @@
 	position = 0;
 	updatePending = false;
 
-	alert(1, 1, 31, "", "");
+	alert(1, 1, 31, "", "", false);
 	assertTrue(isAlertActive());
 
 	cycleDisplay();
@@ -130,7 +130,7 @@
 	extern bool updatePending;
 
 	updatePending = true;
-	alert(1, 1, 31, "", "");
+	alert(1, 1, 31, "", "", false);
 	assertTrue(isAlertActive());
 
 	// update should be skipped if alert is active
diff --git a/lambda-test/interrupts-test.c b/lambda-test/interrupts-test.c
index 238d595..af98d50 100644
--- a/lambda-test/interrupts-test.c
+++ b/lambda-test/interrupts-test.c
@@ -22,6 +22,9 @@
 	// test that the beep output pin is enabled
 	assertTrue(bit_is_set(DDRB, PB1));
 
+	// test that the oxygen sensor heating control output pin is enabled
+	assertTrue(bit_is_set(DDRB, PB1));
+
 	return true;
 }
 
diff --git a/lambda-test/sensors-test.c b/lambda-test/sensors-test.c
index 2df4ae3..cc5bd35 100644
--- a/lambda-test/sensors-test.c
+++ b/lambda-test/sensors-test.c
@@ -72,13 +72,13 @@
 }
 
 bool testToLambdaValue(void) {
-	int16_t lambda = toLambda(132);
+	uint16_t lambda = toLambda(132);
 
 	return lambda == 1500;
 }
 
 bool testToLambdaInter(void) {
-	int16_t lambda = toLambda(550);
+	uint16_t lambda = toLambda(550);
 
 	return lambda == 1073;
 }
diff --git a/lambda/Makefile b/lambda/Makefile
index 69df61a..0fb356a 100644
--- a/lambda/Makefile
+++ b/lambda/Makefile
@@ -13,7 +13,7 @@
 MAIN = lambda.c
 
 ## en: 0 (default), de: 1
-LANG = 0
+LANG = 1
 
 ## If you've split your program into multiple .c / .h files, 
 ## include the additional source (in same directory) here 
diff --git a/lambda/TODO b/lambda/TODO
index a5a43b3..b996cd7 100644
--- a/lambda/TODO
+++ b/lambda/TODO
@@ -11,4 +11,6 @@
 * Circuit
 - Look at oxygen sensor voltage with voltmeter/oscilloscope - is the voltage
   really so unstable?
-- Put button and beeper pins in pins.h (watch out with OCR1A)
\ No newline at end of file
+- Put button and beeper pins in pins.h (watch out with OCR1A)
+- AVcc should be connected to Vcc via an LC network
+- ADC 5 and 4 use digital power while ADC 3-0 use analog power!
\ No newline at end of file
diff --git a/lambda/adc.c b/lambda/adc.c
index b865a86..bfb56d4 100644
--- a/lambda/adc.c
+++ b/lambda/adc.c
@@ -23,7 +23,7 @@
 	ADMUX |= (1 << REFS0);
 	// disable digital input on the ADC inputs
 	// http://www.openmusiclabs.com/learning/digital/atmega-adc/
-	DIDR0 |= (1 << ADC_TEMPI) | (1 << ADC_TEMPO) | (1 << ADC_LAMBDA);
+	DIDR0 = 0b00111111;
 	// ADC clock prescaler/8
 	ADCSRA |= (1 << ADPS1) | (1 << ADPS0);
 	// enable ADC
diff --git a/lambda/alert.c b/lambda/alert.c
index f205339..916874c 100644
--- a/lambda/alert.c
+++ b/lambda/alert.c
@@ -19,6 +19,7 @@
 uint8_t oscCount = 0;
 
 static bool alertActive = false;
+static bool keepActive = false;
 
 void oscillateBeep(void) {
 	if (beepCount == 0) {
@@ -33,7 +34,7 @@
 		// turn beep off
 		TCCR1A &= ~(1 << COM1A0);
 		beepCount--;
-		if (beepCount == 0) {
+		if (beepCount == 0 && ! keepActive) {
 			alertActive = false;
 		}
 	}
@@ -49,32 +50,36 @@
 }
 
 void alert(uint8_t const beeps, uint8_t const length, uint16_t const tone,
-		const char* const line0, const char* const line1) {
+		const char* const line0, const char* const line1,
+		bool const keep) {
 	OCR1A = tone;
 	if (TCNT1 >= tone) TCNT1 = 0;
 	alertActive = true;
 	oscCount = 0;
 	beepCount = beeps;
 	beepLength = length;
+	keepActive = keep;
 	displayText(line0, line1);
 }
 
 void alert_P(uint8_t const beeps, uint8_t const length, uint16_t const tone,
-		PGM_P const line0_P, PGM_P const line1_P) {
+		PGM_P const line0_P, PGM_P const line1_P, bool const keep) {
 	char line0[17];
 	char line1[17];
 	strncpy_P(line0, line0_P, sizeof(line0));
 	strncpy_P(line1, line1_P, sizeof(line1));
 
-	alert(beeps, length, tone, line0, line1);
+	alert(beeps, length, tone, line0, line1, keep);
 }
 
-void cancelAlert(void) {
+void cancelAlert(bool const all) {
 	beepCount = 0;
 	oscCount = 0;
 	// turn beep off
 	TCCR1A &= ~(1 << COM1A0);
-	alertActive = false;
+	if (! keepActive || all) {
+		alertActive = false;
+	}
 }
 
 bool isAlertActive(void) {
diff --git a/lambda/alert.h b/lambda/alert.h
index 20b4e95..6aad976 100644
--- a/lambda/alert.h
+++ b/lambda/alert.h
@@ -26,22 +26,23 @@
 /**
  * Beeps the given number of beeps with the given length and tone and displays
  * the given two texts on the first and second line of the display,
- * respectively.
+ * respectively, and keeps the alert active or not regardless of the beeps.
  */
 void alert(uint8_t beeps, uint8_t length, uint16_t tone,
-		const char* line0, const char* line1);
+		const char* line0, const char* line1, bool keep);
 
 /**
  * Like alert(), but line0_P and line1_P are expected to be static pointers to
  * strings stored in program space like so: PSTR("string").
  */
 void alert_P(uint8_t beeps, uint8_t length, uint16_t tone,
-		PGM_P line0_P, PGM_P line1_P);
+		PGM_P line0_P, PGM_P line1_P, bool keep);
 
 /**
- * Stops beeping and blocking display updates.
+ * Stops beeping and blocking display updates. If all is true, also alerts with
+ * where keep was true are cancelled.
  */
-void cancelAlert(void);
+void cancelAlert(bool all);
 
 /**
  * Returns true if an alert is active, false otherwise.
diff --git a/lambda/command.c b/lambda/command.c
index 5aee933..02c7ffa 100644
--- a/lambda/command.c
+++ b/lambda/command.c
@@ -14,6 +14,7 @@
 #include <string.h>
 #include <avr/pgmspace.h>
 #include <avr/interrupt.h>
+#include "interrupts.h"
 #include "sensors.h"
 #include "display.h"
 #include "alert.h"
@@ -38,13 +39,16 @@
 	split(data, " ", fields, fieldCount);
 	if (strcmp_P(fields[0], PSTR("se")) == 0) {
 		// simulation enable
+		simulation = true;
+		resetTime();
 		resetDisplay();
 		resetRules();
-		simulation = true;
+		setHeatingOn(true);
 		beep(1, 2, 31);
 	}
 	else if (strcmp_P(fields[0], PSTR("sd")) == 0) {
 		// simulation disable
+		resetTime();
 		resetDisplay();
 		resetRules();
 		simulation = false;
@@ -60,6 +64,16 @@
 		logging = false;
 		beep(1, 2, 31);
 	}
+	else if (strcmp_P(fields[0], PSTR("he")) == 0) {
+		// oxygen sensor heating enable
+		setHeatingOn(true);
+		beep(1, 2, 31);
+	}
+	else if (strcmp_P(fields[0], PSTR("hd")) == 0) {
+		// oxygen sensor heating disable
+		setHeatingOn(false);
+		beep(1, 2, 31);
+	}
 	else if (strcmp_P(fields[0], PSTR("cm")) == 0) {
 		// cycle menu
 		cycleDisplay();
@@ -68,7 +82,7 @@
 		// test alert
 		char buf[16];
 		strcpy_P(buf, PSTR("Beep Beep Beep!"));
-		alert(3, 10, 15, buf, fields[1]);
+		alert(3, 10, 15, buf, fields[1], false);
 	}
 	else if (strcmp_P(fields[0], PSTR("tb")) == 0) {
 		// test beep
@@ -84,7 +98,9 @@
 	}
 	else if (simulation) {
 		Measurement meas = readMeas(fields, fieldCount);
-		updateMeas(meas);
+		if (getHeatingState() == HEATING_READY) {
+			updateMeas(meas);
+		}
 		reason(meas);
 	}
 }
diff --git a/lambda/display.c b/lambda/display.c
index 079334d..10dd84e 100644
--- a/lambda/display.c
+++ b/lambda/display.c
@@ -26,8 +26,8 @@
 
 uint8_t position = MENU_OFF;
 bool updatePending = false;
-Measurement measLatest = {0, 0, 0};
-Measurement measMax = {0, 0, 2000};
+Measurement measLatest = {0, 0, 2000, 0};
+Measurement measMax = {0, 0, 2000, 0};
 
 static char lastLine0[17];
 static char lastLine1[17];
@@ -62,7 +62,7 @@
 	updatePending = true;
 	if (isAlertActive()) {
 		// button pressed during alert
-		cancelAlert();
+		cancelAlert(false);
 		return;
 	}
 	position++;
@@ -110,8 +110,8 @@
 void logMeas(Measurement const meas) {
 	char log[64];
 	snprintf(log, sizeof(log),
-			"Ti %3d C - To %3d C - L %4u \r\n",
-			meas.tempI, meas.tempO, meas.lambda);
+			"Ti %3d C - To %3d C - L %u - C %4u\r\n",
+			meas.tempI, meas.tempO, meas.lambda, meas.current);
 	printString(log);
 }
 
diff --git a/lambda/interrupts.c b/lambda/interrupts.c
index 91288d1..454389a 100644
--- a/lambda/interrupts.c
+++ b/lambda/interrupts.c
@@ -12,19 +12,20 @@
 #include <string.h>
 #include <avr/interrupt.h>
 #include <avr/sleep.h>
+#include <util/atomic.h>
 #include "interrupts.h"
 #include "sensors.h"
 #include "display.h"
 #include "alert.h"
 
 static volatile bool buttonPressed = false;
-static volatile uint8_t intCount = 0;
+static volatile uint32_t time = 0;
 
 /**
- * Called every 16 ms.
+ * Called about every 16.4 ms.
  */
 ISR(TIMER0_OVF_vect) {
-	intCount++;
+	time++;
 	oscillateBeep();
 	if (bit_is_clear(PINB, PB0) && ! buttonPressed) {
 		buttonPressed = true;
@@ -34,14 +35,17 @@
 	}
 }
 
-bool hasIntCount(uint8_t const count, bool const reset) {
-	if (intCount >= count) {
-		if (reset) {
-			intCount = 0;
-		}
-		return true;
-	} else {
-		return false;
+uint32_t getTime(void) {
+	uint32_t atomicTime;
+	ATOMIC_BLOCK(ATOMIC_FORCEON) {
+		atomicTime = time;
+	}
+	return atomicTime;
+}
+
+void resetTime(void) {
+	ATOMIC_BLOCK(ATOMIC_FORCEON) {
+		time = 0;
 	}
 }
 
@@ -51,6 +55,9 @@
 
 	// enable beep output pin
 	DDRB |= (1 << PB1);
+
+	// enable oxygen sensor heating control output pin
+	DDRB |= (1 << PB2);
 }
 
 void setupSleepMode(void) {
@@ -76,7 +83,7 @@
 
 void initTimers(void) {
 	// timer in normal mode is default
-	// timer0 clock prescaler/64 = 15.625 kHz overflowing every 16 ms
+	// timer0 clock prescaler/64 = 15.625 kHz overflowing every 16.4 ms
 	TCCR0B |= (1 << CS01) | (1 << CS00);
 
 	// timer1 Clear Timer on Compare Match mode, TOP OCR1A
diff --git a/lambda/interrupts.h b/lambda/interrupts.h
index 5df2368..37ebcd6 100644
--- a/lambda/interrupts.h
+++ b/lambda/interrupts.h
@@ -11,11 +11,17 @@
 #ifndef INTERRUPTS_H_
 #define INTERRUPTS_H_
 
+#define SECOND 61
+
 /**
- * Returns true if the current timer interrupt count is equal or greater to
- * the given count and resets it if the given boolean is true.
+ * Returns the time in units of about 16.4 ms since last reset.
  */
-bool hasIntCount(uint8_t count, bool reset);
+uint32_t getTime(void);
+
+/**
+ * Resets the time to 0.
+ */
+void resetTime(void);
 
 /**
  * Sets up ports.
diff --git a/lambda/lambda.c b/lambda/lambda.c
index f5badd6..f10f0e6 100644
--- a/lambda/lambda.c
+++ b/lambda/lambda.c
@@ -23,6 +23,7 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <avr/pgmspace.h>
+#include <util/delay.h>
 #include "usart.h"
 #include "lcdroutines.h"
 #include "adc.h"
@@ -47,18 +48,24 @@
 	initInterrupts();
 	initTimers();
 
-	alert_P(1, 2, 31, PSTR(MSG_WELCOME), PSTR(""));
+	alert_P(1, 2, 31, PSTR(MSG_WELCOME), PSTR(""), false);
+	// spend some time on being polite
+	_delay_ms(3000);
+	setHeatingOn(true);
 
 	Measurement meas;
 
 	// main loop
-	while (1) {
-		if (hasIntCount(62, true) && ! isSimulation()) {
+	while (true) {
+		if (getTime() % SECOND == 0 && ! isSimulation() &&
+				getHeatingState() != HEATING_FAULT) {
 			meas = measure();
 			if (isLogging()) {
 				logMeas(meas);
 			}
-			updateMeas(meas);
+			if (getHeatingState() == HEATING_READY) {
+				updateMeas(meas);
+			}
 			reason(meas);
 		}
 		if (isUSARTReceived()) {
diff --git a/lambda/messages.h b/lambda/messages.h
index 6540b3b..2b90403 100644
--- a/lambda/messages.h
+++ b/lambda/messages.h
@@ -27,10 +27,15 @@
 	#define MSG_AIRGATE_50_0 "Air gate 50%"
 	#define MSG_AIRGATE_25_0 "Air gate 25%"
 	#define MSG_AIRGATE_CLOSE_0 "Close air gate"
-	#define MSG_AIRGATE_CLOSE_1 "Turn off heating"
 	#define MSG_TOO_RICH_0 "Too rich, open"
 	#define MSG_TOO_RICH_1 "air gate"
 	#define MSG_FIRE_OUT_0 "Fire out?"
+	#define MSG_HEATING_UP_0 "Oxygen sensor"
+	#define MSG_HEATING_UP_1 "heating up..."
+	#define MSG_HEATING_READY_0 "Oxygen sensor"
+	#define MSG_HEATING_READY_1 "ready"
+	#define MSG_HEATING_FAULT_0 "Oxygen sensor"
+	#define MSG_HEATING_FAULT_1 "heating fault!"
 
 #elif LANG == 1
 
@@ -47,10 +52,15 @@
 	#define MSG_AIRGATE_50_0 "Luftschieber 50%"
 	#define MSG_AIRGATE_25_0 "Luftschieber 25%"
 	#define MSG_AIRGATE_CLOSE_0 "Luftschieber zu"
-	#define MSG_AIRGATE_CLOSE_1 "Heizung aus"
 	#define MSG_TOO_RICH_0 "Zu fett, Luft-"
 	#define MSG_TOO_RICH_1 "schieber oeffnen"
 	#define MSG_FIRE_OUT_0 "Feuer aus?"
+	#define MSG_HEATING_UP_0 "Lambdasonde"
+	#define MSG_HEATING_UP_1 "waermt auf..."
+	#define MSG_HEATING_READY_0 "Lambdasonde"
+	#define MSG_HEATING_READY_1 "bereit"
+	#define MSG_HEATING_FAULT_0 "Lambdasonden-"
+	#define MSG_HEATING_FAULT_1 "heizung Fehler!"
 
 #endif
 
diff --git a/lambda/pins.h b/lambda/pins.h
index 328abbd..71748b6 100644
--- a/lambda/pins.h
+++ b/lambda/pins.h
@@ -11,11 +11,13 @@
 #define PINS_H_
 
 /** ADC pin for the type K thermocouple signal */
-#define ADC_TEMPI PC5
+#define ADC_TEMPI PC2
 /** ADC pin for the PT1000 resistance thermometer signal */
-#define ADC_TEMPO PC4	// prototype: PC0
+#define ADC_TEMPO PC0
 /** ADC pin for the LSM 11 oxygen sensor signal */
-#define ADC_LAMBDA PC3	// prototype: PC2
+#define ADC_LAMBDA PC1
+/** ADC pin for the LSM 11 oxygen sensor heating current */
+#define ADC_HEATING PC3
 
 /* Pins for the LCD */
 #define LCD_PORT PORTD
diff --git a/lambda/rules.c b/lambda/rules.c
index 129d119..94c0ea0 100644
--- a/lambda/rules.c
+++ b/lambda/rules.c
@@ -8,10 +8,11 @@
 #include <avr/pgmspace.h>
 #include "alert.h"
 #include "integers.h"
+#include "interrupts.h"
 #include "rules.h"
 #include "messages.h"
 
-#define BEEPS 60
+#define BEEPS 30
 #define LENGTH 20
 #define TONE 31
 
@@ -19,11 +20,11 @@
 #define DIR_BURN_UP 1
 #define DIR_BURN_DOWN -1
 
-uint16_t age = 0;
+uint8_t age = 0;
 int8_t dir = 0;
 
-static Measurement rulesMeasMax = {0, 0, 2000};
-static Measurement rulesMeasPrev = {0, 0, 2000};
+static Measurement rulesMeasMax = {0, 0, 2000, 0};
+static Measurement rulesMeasPrev = {0, 0, 2000, 0};
 
 /**
  * Reminds to set the air gate to 50% when the fire is still building up
@@ -32,7 +33,7 @@
 static void airgate50(bool* const fired, int8_t const dir,
 		Measurement const meas) {
 	if (! *fired && dir == DIR_BURN_UP && meas.tempI >= 500) {
-		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_AIRGATE_50_0), PSTR(""));
+		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_AIRGATE_50_0), PSTR(""), false);
 		*fired = true;
 	}
 }
@@ -44,7 +45,7 @@
 static void airgate25(bool* const fired, int8_t const dir,
 		Measurement const meas) {
 	if (! *fired && dir == DIR_BURN_DOWN && meas.tempI < 800) {
-		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_AIRGATE_25_0), PSTR(""));
+		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_AIRGATE_25_0), PSTR(""), false);
 		*fired = true;
 	}
 }
@@ -56,8 +57,9 @@
 static void airgateClose(bool* const fired, int8_t const dir,
 		Measurement const meas) {
 	if (! *fired && dir == DIR_BURN_DOWN && meas.tempI < 400) {
+		setHeatingOn(false);
 		alert_P(BEEPS, LENGTH, TONE,
-				PSTR(MSG_AIRGATE_CLOSE_0), PSTR(MSG_AIRGATE_CLOSE_1));
+				PSTR(MSG_AIRGATE_CLOSE_0), PSTR(""), false);
 		*fired = true;
 	}
 }
@@ -68,9 +70,10 @@
  */
 static void tooRich(bool* const fired, int8_t const dir,
 		Measurement const meas) {
-	if (! *fired && meas.tempI >= 100 && meas.lambda < 1200) {
+	if (! *fired && meas.tempI >= 100 && meas.lambda < 1200 &&
+			getHeatingState() == HEATING_READY) {
 		alert_P(BEEPS, LENGTH, TONE,
-				PSTR(MSG_TOO_RICH_0), PSTR(MSG_TOO_RICH_1));
+				PSTR(MSG_TOO_RICH_0), PSTR(MSG_TOO_RICH_1), false);
 		*fired = true;
 	}
 	if (meas.lambda >= 1300) {
@@ -85,7 +88,7 @@
 		Measurement const meas) {
 	if (! *fired && dir == DIR_BURN_UP && meas.tempI < 100 &&
 			rulesMeasMax.tempI - meas.tempI > 25) {
-		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_FIRE_OUT_0), PSTR(""));
+		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_FIRE_OUT_0), PSTR(""), false);
 		*fired = true;
 	}
 	if (meas.tempI >= 125) {
@@ -93,10 +96,39 @@
 	}
 }
 
+static void heatingReady(bool* const fired, int8_t const dir,
+		Measurement const meas) {
+	if (! isHeatingOn() || getHeatingState() == HEATING_READY) {
+		return;
+	}
+	if (meas.current <= HEATING_READY_MA && meas.current > HEATING_DISCONN_MA) {
+		setHeatingState(HEATING_READY);
+		alert_P(3, 10, TONE, PSTR(MSG_HEATING_READY_0),
+				PSTR(MSG_HEATING_READY_1), false);
+	}
+}
+
+static void heatingFault(bool* const fired, int8_t const dir,
+		Measurement const meas) {
+	if (! isHeatingOn() || getHeatingState() == HEATING_FAULT) {
+		return;
+	}
+	if (meas.current > HEATING_SHORT_MA || meas.current < HEATING_DISCONN_MA ||
+			(getTime() > SECOND * 120 && meas.current > HEATING_READY_MA)) {
+		// short circuit or disconnected or did not warm up within 2 minutes
+		setHeatingOn(false);
+		setHeatingState(HEATING_FAULT);
+		alert_P(BEEPS, LENGTH, TONE, PSTR(MSG_HEATING_FAULT_0),
+				PSTR(MSG_HEATING_FAULT_1), true);
+	}
+}
+
 /**
  * Array of rules.
  */
 Rule rules[] = {
+		{false, heatingReady},
+		{false, heatingFault},
 		{false, airgate50},
 		{false, airgate25},
 		{false, airgateClose},
@@ -107,13 +139,13 @@
 // called about every second
 void reason(Measurement const meas) {
 
-	// apply the rules about every 10 seconds
-	if (age % 10 == 0) {
+	// apply the rules about every 10 seconds to every 10th measurement
+	// if (age % 10 == 0) {
 		size_t rulesSize = sizeof(rules) / sizeof(rules[0]);
 		for (size_t i = 0; i < rulesSize; i++) {
 			rules[i].cond(&(rules[i].fired), dir, meas);
 		}
-	}
+	// }
 
 	age++;
 
@@ -134,18 +166,15 @@
 	}
 
 	rulesMeasMax.tempI = MAX(rulesMeasMax.tempI, meas.tempI);
-	rulesMeasMax.tempO = MAX(rulesMeasMax.tempO, meas.tempO);
-	rulesMeasMax.lambda = MIN(rulesMeasMax.lambda, meas.lambda);
 }
 
 void resetRules(void) {
 	rulesMeasPrev.tempI = 0;
 	rulesMeasPrev.tempO = 0;
 	rulesMeasPrev.lambda = 2000;
+	rulesMeasPrev.current = 0;
 
 	rulesMeasMax.tempI = 0;
-	rulesMeasMax.tempO = 0;
-	rulesMeasMax.lambda = 2000;
 
 	age = 0;
 	dir = DIR_NONE;
diff --git a/lambda/sensors.c b/lambda/sensors.c
index fd4b18b..ebaa14c 100644
--- a/lambda/sensors.c
+++ b/lambda/sensors.c
@@ -8,15 +8,21 @@
  *
  */
 
+#include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
 #include <avr/io.h>
+#include <util/delay.h>
 #include "adc.h"
+#include "alert.h"
 #include "sensors.h"
 #include "integers.h"
+#include "interrupts.h"
 #include "pins.h"
 #include "messages.h"
 
+static int8_t heatingState = HEATING_OFF;
+
 /**
  * Table used to look up the lambda value at 12 V heater voltage
  * and 220°C exhaust gas temperature. Most values are approximated
@@ -85,24 +91,26 @@
 	meas.tempI = toTempI(tempIVoltageAvg >> 3);
 	meas.tempO = toTempO(tempOVoltageAvg >> 3);
 	meas.lambda = toLambda(lambdaVoltageAvg >> 3);
+	meas.current = toCurrent(getVoltage(ADC_HEATING));
 
 	return meas;
 }
 
 Measurement readMeas(char* const fields[], size_t const size) {
 	Measurement meas;
-	if (size < 3) {
+	if (size < 4) {
 		return meas;
 	}
 	meas.tempI  = atoi(fields[0]);
 	meas.tempO  = atoi(fields[1]);
 	meas.lambda = atoi(fields[2]);
+	meas.current = atoi(fields[3]);
 
 	return meas;
 }
 
 int16_t toTempI(uint16_t const mV) {
-	int temp = divRoundNearest(mV, 5);
+	int16_t temp = divRoundNearest(mV, 5);
 
 	return temp;
 }
@@ -114,13 +122,19 @@
 	return temp;
 }
 
-int16_t toLambda(uint16_t const mV) {
+uint16_t toLambda(uint16_t const mV) {
 	size_t size = sizeof(lambdaTable) / sizeof(lambdaTable[0]);
 	int16_t lambda = lookupLinInter(mV, lambdaTable, size);
 
 	return lambda;
 }
 
+uint16_t toCurrent(uint16_t const mV) {
+	uint16_t current = mV * (1000 / SHUNT_MILLIOHMS);
+
+	return current;
+}
+
 int16_t lookupLinInter(uint16_t const mV, TableEntry const table[],
 		size_t const size) {
 	if (mV < table[0].mV) {
@@ -155,3 +169,27 @@
 		return MSG_RICH;
 	}
 }
+
+void setHeatingOn(bool on) {
+	if (on) {
+		PORTB |= (1 << PB2);
+		heatingState = HEATING_UP;
+		alert_P(1, 2, 31, PSTR(MSG_HEATING_UP_0), PSTR(MSG_HEATING_UP_1), true);
+	} else {
+		PORTB &= ~(1 << PB2);
+		heatingState = HEATING_OFF;
+		cancelAlert(true);
+	}
+}
+
+bool isHeatingOn(void) {
+	return bit_is_set(PORTB, PB2);
+}
+
+void setHeatingState(int8_t state) {
+	heatingState = state;
+}
+
+int8_t getHeatingState(void) {
+	return heatingState;
+}
diff --git a/lambda/sensors.h b/lambda/sensors.h
index 31f229b..c3c497c 100644
--- a/lambda/sensors.h
+++ b/lambda/sensors.h
@@ -13,6 +13,16 @@
 
 #include <stdio.h>
 
+#define SHUNT_MILLIOHMS 100
+#define HEATING_READY_MA 1500
+#define HEATING_SHORT_MA 9000
+#define HEATING_DISCONN_MA 100
+
+#define HEATING_FAULT -1
+#define HEATING_OFF 0
+#define HEATING_UP 1
+#define HEATING_READY 2
+
 /**
  * Entry for the lookup tables.
  */
@@ -27,7 +37,8 @@
 typedef struct {
 	int16_t tempI;
 	int16_t tempO;
-	int16_t lambda;
+	uint16_t lambda;
+	uint16_t current;
 } Measurement;
 
 /**
@@ -66,7 +77,12 @@
  * With the current circuit and the AD8551 the measuring range is from about
  * lambda 1.0 to 2.0 at 5000 mV OP supply and ADC reference voltage.
  */
-int16_t toLambda(uint16_t mV);
+uint16_t toLambda(uint16_t mV);
+
+/**
+ * Returns the current of the oxygen sensor heating in mA.
+ */
+uint16_t toCurrent(uint16_t mv);
 
 /**
  * Returns the value corresponding to the given voltage
@@ -83,4 +99,25 @@
  */
 char* toInfo(uint16_t lambda);
 
+/**
+ * Turns the heating of the oxygen sensor on or off.
+ */
+void setHeatingOn(bool on);
+
+/**
+ * Returns true if the heating of the oxygen sensor is turned on,
+ * false otherwise.
+ */
+bool isHeatingOn(void);
+
+/**
+ * Sets the state of the heating of the oxygen sensor to the given value.
+ */
+void setHeatingState(int8_t state);
+
+/**
+ * Returns the state of the heating of the oxygen sensor.
+ */
+int8_t getHeatingState(void);
+
 #endif /* SENSORS_H_ */