Audi - Side Assist Retrofit - Le Cazzate Di Vicenza

How to retrofit Audi Side Assist, Exit Warning, Rear Cross Traffic Assist and Pre Sense rear on an Audi A4 B9: parts, rear radars, door wiring, Component Protection and coding

This guide describes how to retrofit Audi Side Assist on an Audi A4 B9 using the third-generation Bosch rear radars. The same two radars also enable Exit Warning, Rear Cross Traffic Assist and Pre Sense rear. The retrofit requires the two rear radars with their brackets, the warning LEDs in the mirrors and in the doors, door control units that support these functions, Component Protection removal with ODIS and the coding of several modules.

✅ Status: working

100%

This retrofit has been successfully installed and tested on my Audi A4 B9, and it is still active.

1. What this retrofit enables
2. Needed parts and price
3. How the system works
4. Procedure
5. Notes: aftermarket mirror LEDs
6. Summary

Bosch rear radar mounted on its bracket inside the rear bumper of the Audi A4 B9 — **Figure 1** – Rear radar mounted inside the rear bumper

1. What this retrofit enables

Function	Description
Side Assist	Also known as SWA (Spurwechselassistent) or BSD (blind spot detection): warns with an LED in the exterior mirror when a vehicle is in the blind spot or approaching fast from behind
Exit Warning	Visual warning that alerts occupants when vehicles or cyclists are approaching from behind as the doors are opened
Rear Cross Traffic Assist	Also known as RCTA: monitors the area behind the car while reversing and warns of vehicles and other objects approaching from the sides
Pre Sense rear	Warns when a rear collision is imminent; it closes windows and sunroof, activates the hazard lights and tensions the seat belts, if equipped

2. Needed parts and price

Group	Part number	Qty	Description
Radars	`4M0 907 566 D`	1	Right rear radar [MASTER]
	`4M0 907 590 D`	1	Left rear radar [SLAVE]
	`8W0 907 175`	1	Left radar bracket [sedan]
	`8W0 907 176`	1	Right radar bracket [sedan]
Exit Warning LEDs	`8W0 947 356 B`	2	Front Exit Warning LED
	`8W0 947 356 H`	2	Rear Exit Warning LED
	`4B0 972 623`	4	Exit Warning LED connector
	`1K0 972 923`	2	Connector for rear door ECUs
Connectors and pins	`1-968700-1`	4	Splitter connector
Connectors and pins	`N90764701`	10	Female pin connectors
Door ECUs	`4M0 959 792 C`	1	Front passenger side
	`4M0 959 793 C`	1	Front driver side
	`4M0 959 795 C`	–	Rear side

Diagnostic tools: VAS interface with ODIS online for Component Protection removal, and VCDS for coding. The total cost of the retrofit was about 800 €.

ℹ️ Sedan brackets

The bracket part numbers listed above are for the sedan. On the Avant the bumper is different: check the correct brackets for your body type before ordering.

3. How the system works

The pages below come from the Audi self-study programme on the third-generation rear radar. The two radars (J769 master and J770 slave) talk to each other over a Private CAN bus and are both connected to the Extended CAN bus. The mirror warning lamps K233 and K234 are driven by the front door control units J386 and J387, while the exit warning lamps W111–W114 are driven by the respective door control units.

Overview of the third-generation rear radar: J769 and J770 on Private and Extended CAN, J533 gateway, door control units J386, J387, J926, J927 with warning lamps K233, K234 and W111-W114 — **Figure 2** – System overview: radars, gateway, door control units and warning lamps

Rear radar sensors: J769 master control unit on the right and J770 slave control unit, connected via Private CAN and Extended CAN — **Figure 3** – Rear radar sensors: J769 master (right side) and J770 slave

Comparison table between second-generation Hella 24 GHz and third-generation Bosch 77 GHz radar sensors — **Figure 4** – Second-generation (Hella, 24 GHz) vs third-generation (Bosch, 77 GHz) radar

Area covered by the rear radar sensors: rearward beam, sideways beam and total monitored area up to 50 m on each side — **Figure 5** – Area covered by the sensors: rearward beam, sideways beam and total area

Rear Cross Traffic Assist warnings: collision probability table and visual, audible and tactile warnings — **Figure 6** – Rear Cross Traffic Assist: visual, audible and tactile warnings

4. Procedure

4.1 Mounting the radars

The rear bumper must be removed. Fit the brackets in the bumper at the points circled in red, then mount the radars: the master (4M0 907 566 D) on the right and the slave (4M0 907 590 D) on the left.

Rear bumper with the bracket fixing points circled in red, the radar wiring and the radar mounted on its bracket — **Figure 7** – Bracket fixing points, radar wiring and radar mounted in the bumper

4.2 Wiring the radars

Both radars use an 8-pin connector (T8j on J769, T8q on J770) with the same pin assignment:

Pin	Function
1	Terminal 31 (earth)
2	Extended CAN high
3	Extended CAN low
5 – 6	Private CAN between master and slave
8	Terminal 30 (permanent positive)

On the A4 B9 the Extended CAN reaches the gateway J533 through the coupling point in the left side of the luggage compartment (THRL), and the master radar is powered by fuse SF4 in fuse holder ST3 of the SR2 carrier. Check the details in the wiring diagrams:

Audi A4 current flow diagram 35/2: lane change assist control unit J769 with connector T8j, fuse SF4, coupling point THRL and Extended CAN connections — **Figure 8** – Wiring diagram 35/2: master radar J769

Audi A4 current flow diagram 35/3: lane change assist control unit 2 J770 with connector T8q and Extended CAN connection to gateway J533 — **Figure 9** – Wiring diagram 35/3: slave radar J770 and gateway J533

4.3 Wiring the front doors

The Side Assist warning lamps in the exterior mirrors (K233 driver side, K234 passenger side) are driven by the front door control units J386 and J387. The red arrows in the photos show the pins to populate on the mirror connector:

Audi A4 current flow diagram 35/4: driver and passenger exterior mirrors with lane change assist warning lamps K233 and K234 connected to J386 and J387, with photos of the mirror connectors — **Figure 10** – Wiring diagram 35/4: mirror warning lamps K233 and K234

The front Exit Warning lamps (W111 driver side, W112 passenger side) are connected to the 32-pin connector of the door control unit (pin 6: T32a/6 on J386, T32b/6 on J387) and to the door earth point. Use the 4B0 972 623 connectors for the LEDs and the N90764701 pins for the door control unit connector:

Audi A4 current flow diagram 3/22: front passenger door control unit J387 with exit warning lamp W112 on T32b/6, LED connector and door ECU connector photo — **Figure 11** – Wiring diagram 3/22: passenger door J387 and Exit Warning lamp W112

Audi A4 current flow diagram 3/17: driver door control unit J386 with exit warning lamp W111 on T32a/6 and mirror warning lamp K233 — **Figure 12** – Wiring diagram 3/17: driver door J386 and Exit Warning lamp W111

4.4 Wiring the rear doors

The rear Exit Warning lamps (W113 driver side, W114 passenger side) are driven by the rear door control units J926 and J927. On the driver side the lamp is connected to pin T6ao/1 of J926 and to the door earth point; use the 1K0 972 923 connector on the rear door control unit:

Audi A4 current flow diagram 3/28: rear driver side door control unit J926 with rear exit warning lamp W113 on T6ao/1 and photo of the 6-pin connector — **Figure 13** – Wiring diagram 3/28: rear door J926 and Exit Warning lamp W113

4.5 Component Protection removal

The radars and the door control units come from other cars and are protected by Component Protection: remove it with ODIS online. Start the Component protection adapt gateway sequence and follow the instructions: connect the tester to the online network and to the car, then wake up the data bus by switching the headlights briefly on and off.

ODIS Service: Component protection adapt gateway sequence with the instructions to connect the tester and wake up the data bus — **Figure 14** – ODIS: start of the Component protection adapt gateway sequence

At the end ODIS lists the control units that have been adapted. Among them you must find K3C – Lane change assistance and KCF – Lane change assistant 2, i.e. the two radars:

ODIS: list of control units successfully adapted, including K3C Lane change assistance and KCF Lane change assistant 2 — **Figure 15** – ODIS: control units adapted, including the two radars K3C and KCF

ODIS test plan with the 19 - Data bus diag interface, component protection test completed with green check — **Figure 16** – ODIS: Component Protection test completed

⚠️ Keep the battery charged

The procedure keeps the car awake for a long time with many control units active: connect a battery charger or power supply before starting. In the screenshots the voltage had already dropped below 12 V.

4.6 Coding

Code the following modules with VCDS. In the tables, "Byte X bit Y = 1" means that the bit must be enabled in the long coding.

03 ABS – Long coding

Byte	Change	With AutoHold	Without AutoHold
18	bit 3 = 1	`DA` [11011010]	`9A` [10011010]
30	bit 4 = 1	`5B` [01011011]	`59` [01011001]

ℹ️ ABS reference values

The hexadecimal values are those of my car. On your car, start from your own coding and only enable the bits shown in the Change column.

Other modules

Module	Type	Change
17 Instruments	Long coding	Byte 5 bit 3 = 1 [Lane change assistance]
A5 Front camera	Long coding	Byte 11 bit 1 = 1 [SWA]
09 Central Electrics	Long coding	Byte 37 bit 0 = 1 [rtca_support_config]
42 Door Elect Driver	Long coding	Byte 11 bit 4 = 1 [SWA] Byte 11 bit 5 = 1 [Exit Warning]
52 Door Elect Pass	Long coding	Byte 11 bit 4 = 1 [SWA] Byte 11 bit 5 = 1 [Exit Warning]
BB – BC Rear doors	Long coding	Byte 11 bit 4 = 1 [SWA] Byte 11 bit 5 = 1 [Exit Warning]

5F Information Electronics – Adaptation

Channel	Value
`SWA_0x1A`	activated
`SWA_0x1A_msg_bus`	Terminal 15
`[LO]_menu_display_lane_assistant`	activated
`[LO]_menu_display_lane_assistant_over_threshold_high`	activated

5. Notes: aftermarket mirror LEDs

I first bought an aftermarket Audi Side Assist kit from AliExpress, and the Side Assist LEDs in the mirrors did not work. The driver door control unit (42) reported this fault:

⚠️ 196885 – Function Lighting for Lane Change Assistant LED Display

B1789 01 [009] – Electrical Failure

After some troubleshooting and advice, it turned out that the problem was the aftermarket LEDs. I bought a pair of original ones (100 € for left and right!) and now everything works perfectly.

Side Assist LED lit in the driver side exterior mirror with a car in the blind spot — **Figure 18** – Side Assist LED lit in the mirror with the original LED

Note the differences between the Chinese LED and the original one: the OEM part is rated 5.5 V / 0.77 W, the Chinese one 7.2 V / 0.4 W.

Comparison between the OEM mirror LED rated 5.5 V 0.77 W and the Chinese one rated 7.2 V 0.4 W — **Figure 19** – OEM LED (5.5 V / 0.77 W) vs Chinese LED (7.2 V / 0.4 W)

💡 Buy original mirror LEDs

If you get fault B1789 on the door modules after the retrofit, check the wiring first, then the mirror LEDs: the electrical ratings of the aftermarket parts do not match what the door control unit expects.

6. Summary

Step	What to do
Radars	Remove the rear bumper, fit brackets and radars: master on the right, slave on the left (section 4.1)
Radar wiring	Terminal 30/31, Extended CAN to J533, Private CAN between radars (section 4.2)
Front doors	Mirror LEDs K233/K234 and Exit Warning lamps W111/W112 (section 4.3)
Rear doors	Exit Warning lamps W113/W114 on J926/J927 (section 4.4)
Component Protection	ODIS online: check that K3C and KCF are adapted (section 4.5)
Coding	03, 17, 5F, A5, 09, 42, 52, BB/BC (section 4.6)
Fault B1789 on mirror LED	Replace aftermarket LEDs with original ones (section 5)