diff --git a/src/add-ons/accelerants/nvidia/engine/nv_brooktreetv.c b/src/add-ons/accelerants/nvidia/engine/nv_brooktreetv.c
index 7344bd6cf1..938f596ddc 100644
--- a/src/add-ons/accelerants/nvidia/engine/nv_brooktreetv.c
+++ b/src/add-ons/accelerants/nvidia/engine/nv_brooktreetv.c
@@ -215,47 +215,31 @@ static uint8 BT_read_type (void)
 
 bool BT_probe()
 {
+	uint8 bus;
 	bool btfound = false;
+	bool *i2c_bus = &(si->ps.i2c_bus0);
 
-	LOG(4,("Brooktree: Checking I2C bus(ses) for first possible TV encoder...\n"));
-	if (si->ps.i2c_bus0)
+	LOG(4,("Brooktree: Checking wired I2C bus(ses) for first possible TV encoder...\n"));
+	for (bus = 0; bus < 3; bus++)
 	{
-		/* try primary adress on bus 0 */
-		if (!BT_check(0, PRADR))
+		if (i2c_bus[bus] && !btfound)
 		{
-			btfound = true;
-			si->ps.tv_encoder.adress = PRADR;
-			si->ps.tv_encoder.bus = 0;
-		}
-		else
-		{
-			/* try secondary adress on bus 0 */
-			if (!BT_check(0, SCADR))
+			/* try primary adress on bus */
+			if (!BT_check(bus, PRADR))
 			{
 				btfound = true;
-				si->ps.tv_encoder.adress = SCADR;
-				si->ps.tv_encoder.bus = 0;
+				si->ps.tv_encoder.adress = PRADR;
+				si->ps.tv_encoder.bus = bus;
 			}
-		}
-	}
-
-	if (si->ps.i2c_bus1 && !btfound)
-	{
-		/* try primary adress on bus 1 */
-		if (!BT_check(1, PRADR))
-		{
-			btfound = true;
-			si->ps.tv_encoder.adress = PRADR;
-			si->ps.tv_encoder.bus = 1;
-		}
-		else
-		{
-			/* try secondary adress on bus 1 */
-			if (!BT_check(1, SCADR))
+			else
 			{
-				btfound = true;
-				si->ps.tv_encoder.adress = SCADR;
-				si->ps.tv_encoder.bus = 1;
+				/* try secondary adress on bus */
+				if (!BT_check(bus, SCADR))
+				{
+					btfound = true;
+					si->ps.tv_encoder.adress = SCADR;
+					si->ps.tv_encoder.bus = bus;
+				}
 			}
 		}
 	}
diff --git a/src/add-ons/accelerants/nvidia/engine/nv_i2c.c b/src/add-ons/accelerants/nvidia/engine/nv_i2c.c
index 8cb8b02944..1106604377 100644
--- a/src/add-ons/accelerants/nvidia/engine/nv_i2c.c
+++ b/src/add-ons/accelerants/nvidia/engine/nv_i2c.c
@@ -24,11 +24,29 @@ char i2c_flag_error (char ErrNo)
 	return I2CError;
 }
 
+static void i2c_select_bus_set(bool set)
+{
+	/* I/O pins set selection is only valid on dualhead cards */
+	if (!si->ps.secondary_head) return;
+
+	/* select GPU I/O pins set to connect to I2C 'registers' */
+	if (set)
+	{
+		NV_REG32(NV32_FUNCSEL) &= ~0x00000010;
+		NV_REG32(NV32_2FUNCSEL) |= 0x00000010;
+	}
+	else
+	{
+		NV_REG32(NV32_2FUNCSEL) &= ~0x00000010;
+		NV_REG32(NV32_FUNCSEL) |= 0x00000010;
+	}
+}
+
 static void OutSCL(uint8 BusNR, bool Bit)
 {
 	uint8 data;
 
-	if (BusNR)
+	if (BusNR & 0x01)
 	{
 		data = (CRTCR(WR_I2CBUS_1) & 0xf0) | 0x01;
 		if (Bit)
@@ -50,7 +68,7 @@ static void OutSDA(uint8 BusNR, bool Bit)
 {
 	uint8 data;
 	
-	if (BusNR)
+	if (BusNR & 0x01)
 	{
 		data = (CRTCR(WR_I2CBUS_1) & 0xf0) | 0x01;
 		if (Bit)
@@ -70,7 +88,7 @@ static void OutSDA(uint8 BusNR, bool Bit)
 
 static bool InSCL(uint8 BusNR)
 {
-	if (BusNR)
+	if (BusNR & 0x01)
 	{
 		if ((CRTCR(RD_I2CBUS_1) & 0x04)) return true;
 	}
@@ -84,7 +102,7 @@ static bool InSCL(uint8 BusNR)
 
 static bool InSDA(uint8 BusNR)
 {
-	if (BusNR)
+	if (BusNR & 0x01)
 	{
 		if ((CRTCR(RD_I2CBUS_1) & 0x08)) return true;
 	}
@@ -142,6 +160,9 @@ static uint8 RXBit (uint8 BusNR)
 
 void i2c_bstart (uint8 BusNR)
 {
+	/* select GPU I/O pins set */
+	i2c_select_bus_set(BusNR & 0x02);
+
 	/* enable access to primary head */
 	set_crtc_owner(0);
 
@@ -164,6 +185,9 @@ void i2c_bstart (uint8 BusNR)
 
 void i2c_bstop (uint8 BusNR)
 {
+	/* select GPU I/O pins set */
+	i2c_select_bus_set(BusNR & 0x02);
+
 	/* enable access to primary head */
 	set_crtc_owner(0);
 
@@ -188,6 +212,9 @@ uint8 i2c_readbyte(uint8 BusNR, bool Ack)
 {
 	uint8 cnt, bit, byte = 0;
 
+	/* select GPU I/O pins set */
+	i2c_select_bus_set(BusNR & 0x02);
+
 	/* enable access to primary head */
 	set_crtc_owner(0);
 
@@ -213,6 +240,9 @@ bool i2c_writebyte (uint8 BusNR, uint8 byte)
 	bool bit;
 	uint8 tmp = byte;
 
+	/* select GPU I/O pins set */
+	i2c_select_bus_set(BusNR & 0x02);
+
 	/* enable access to primary head */
 	set_crtc_owner(0);
 
@@ -255,8 +285,9 @@ void i2c_writebuffer (uint8 BusNR, uint8* buf, uint8 size)
 
 status_t i2c_init(void)
 {
-	uint8 bus;
+	uint8 bus, buses;
 	bool *i2c_bus = &(si->ps.i2c_bus0);
+	status_t result = B_ERROR;
 
 	LOG(4,("I2C: searching for wired I2C buses...\n"));
 
@@ -266,9 +297,15 @@ status_t i2c_init(void)
 	/* preset no board wired buses */
 	si->ps.i2c_bus0 = false;
 	si->ps.i2c_bus1 = false;
+	si->ps.i2c_bus2 = false;
+	si->ps.i2c_bus3 = false;
 
-	/* find existing buses */	
-	for (bus = 0; bus < 2; bus++)
+	/* set number of buses to test for */
+	buses = 2;
+	if (si->ps.secondary_head) buses = 4;
+
+	/* find existing buses */
+	for (bus = 0; bus < buses; bus++)
 	{
 		/* reset status */
 		i2c_flag_error (-1);
@@ -292,14 +329,16 @@ status_t i2c_init(void)
 		i2c_bstop(bus);
 	}
 
-	for (bus = 0; bus < 2; bus++)
+	for (bus = 0; bus < buses; bus++)
 	{
 		if (i2c_bus[bus])
+		{
 			LOG(4,("I2C: bus #%d wiring check: passed\n", bus));
+			result = B_OK;
+		}
 		else
 			LOG(4,("I2C: bus #%d wiring check: failed\n", bus));
 	}
 
-	if (!si->ps.i2c_bus0 && !si->ps.i2c_bus1) return B_ERROR;
-	return B_OK;
+	return result;
 }