BMW E8x E9x Cruise Control Retrofit (SA540) [Full Guide]

This is the complete guide to Cruise Control Retrofit for BMW E8x/E9x. In this in-depth guide you’ll learn:

• How to replace the SZL module
• How to code the retrofit
• How to calibrate the steering angle sensor
• Lots more

Let’s get started.

Introduction

The cruise control retrofit on E9x and E8x BMWs is one of the best mods you can make for your car. While some models are quite simple, the others require some advanced skills. This guide is about basic cruise control (option code 540).

 

Installation time

The installation time is approx. 20 minutes including coding work. This may differ based on the car’s condition and equipment package. However, the most important factor will be your skill. After countless retrofits, I usually spend about 10 minutes including the test drive.

E90 Cruise Control Versions

The following cruise control options were available for E90 from the model year 2005.

Option 540 – Cruise Control 

The desired (set) speed is maintained by the engine without brake intervention. So, when you go downhill, the engine drag torque will decelerate the car. 

Option 544 – Cruise Control With Brake Function

The desired (set) speed is maintained by both engine and brake intervention. In this case, the DCS control module will activate the brakes to maintain the desired speed when engine drag torque is not sufficient to decelerate the car. 

Here’s the guide for this retrofit.

Option 541 – Active Cruise Control 

The driver accelerates the vehicle to the desired speed and then hits the set button; the vehicle then maintains that speed. The ‘active’ component is that your BMW will slow down if it detects a slower-moving vehicle in front of it. That’s ideal for lengthy drives and interstate driving, especially in traffic.

Here’s the guide for this retrofit.

The Difference Between Cruise Control for 6 and 4-cylinder Engines

For the 4-cylinder BMW E90 (E8x, E9x) the retrofit includes only replacing the steering column switch cluster (SZL) and steering column lower trim section.

While 6-cylinder E90s usually have the cruise control as a standard equipment package, on some markets and some models it was optional. The difference is that straight-six powered E90s do not support the basic version of cruise control (SA540). So, they can be retrofitted with either Cruise Control With Brake Function (SA544) or Active Cruise Control (SA541).  

In the E90/E91/E92 up to 09/2006, the cruise control is managed via a separate control unit: the LDM (Longitudinal Dynamics Management). 

As of 09/2006 (E92 06/2002), the cruise control with braking function is integrated into the DSC control unit, and the LDM control unit is therefore eliminated. 

 

 

 

 

Cruise Control Retrofit

Let’s get started.

 

Part List For Retrofit 

Steering Column Switch Cluster (SZL)
Be aware of the rear wiper! The automatic wiper function will work on cars without the rain sensor and vice versa. The only difference is the LED light on the wiper control stalk. 

Steering column lower trim section. 
All models are interchangeable – i.e. The E87 part will fit E84 or E92. 

 

Tools 

• 10mm wrench (for battery cable)
• 16mm socket with ratchet
• Torx T25 screwdriver
• Small flat screwdriver

 

Retrofit Procedure

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Remove Steering Wheel

1.1 Disconnect Battery Negative Lead

Loosen nut (1)

Disconnect the battery earth lead (3) and push at the side.

1.2 Remove Driver’s Airbag

Insert a Torx screwdriver (T25) into the hidden opening on the backside of the steering wheel at an angle until spring resistance is felt (approx. 1.5 cm).

Using a Torx screwdriver (T25), push the spring leg (concealed) until the airbag unit is freed.

Carry on with the same procedure on the other side.

Tilt airbag unit backward.

Disconnect plug connections and remove the airbag.

 

Replace Steering Column Switch Cluster (SZL)

Adjust the steering column to “bottom” and “extended.”

Remove lower section of the steering column trim

Unclip steering column trim downwards by pressing detent lugs outward a little. 

Remove SZL

Remove 4 screws (1) with Torx t25 screwdriver.

Pull back the steering column switch cluster (2) in the arrow’s direction and disconnect the plug connections behind it (2).

 

Concluding Work And Coding

Now we need to give some modules instructions on how to behave with our newly retrofitted cruise control. You can code your BMW with ISTA, various coding apps, or with NCS Expert. The latter is my tool of choice. 

 

Cruise Control Retrofit Coding

Follow this guide to learn more about NCS Expert coding. 

Cruise Control VO Coding 

Add $540 code to vehicle FA.

Code KOMBI and DSC. The SZL module can’t be coded, and the DSC acts as a gateway, so the DSC will transfer the coding to the SZL module. (In E60, F10, and others, SZL can be coded directly. 

Calibrating Steering Wheel Sensor 

On very rare occasions, you don’t need to calibrate the steering angle sensor. In my experience one in ten. But most of them would need it. There are two ways to do it. You can either use ISTA or Tool32, which is my tool of choice. 

Here’s how to do it.

In NCS Expert find the SGBD name of the DSC unit, in this case, DSC_89.prg. XDSC means that this version is for xDrive BMW. 

Set the steering wheel in a straight position, visual is enough.

Open Toolset 32 application and load DSC_89.prg file [File –> Load SGBD –>choose DSC_89.prg].

Find “lenkwinkel_dsc_abgleich” and click twice.

The coding and steering angle sensor calibration is done. Now we need to clear error memory. It doesn’t affect the operation, but it is a good practice to always clear the error memory after the work is done.

 

Now head over to INPA and clear all error memories with “FUNCTIONAL JOBS”. This will erase all diagnostic trouble codes in all control modules at once. 

Install lower trim

Install by aligning the steering column trim to the steering column using the detent lugs and pressing up as far as it will go.

Press the steering column trim on both sides together, then press all the way up until the detent lugs are in position.

Install Airbag

Ensure that the electrical leads are properly positioned during installation.

Snap airbag unit into the steering wheel with uniform pressing force plane parallel to steering column shaft.

Installation:

Connect plugs to connections of the same color on the airbag unit.

 

Now you are ready for a test drive and function check. 

 

How Does BMW E90 Cruise Control Work

The steering column lever for the cruise-control system is fitted on the left-hand side of the steering column.

Description of operation of the steering column lever:

–	Pressing the steering column lever at the side (I/O): Activates cruise control Or: Resumption of cruise-control system. The vehicle accelerates or decelerates exclusively from non-controlled operation to the driving speed of the last set and maintains this speed.
–	Pressing the steering column lever upwards or downwards (off): Cruise-control system off.
–	Pressing the steering column lever briefly backward (+): Sets the road speed. If the cruise control function is activated, the current vehicle speed is kept constant.
–	Pressing and holding the steering column lever backward (+): Increases the road speed. The vehicle accelerates for the period the switch is actuated up to its maximum speed.
–	Pressing the steering column lever briefly forwards or holding pressed (-): Brakes the road speed. The cruise-control system is deactivated for the period the switch is actuated. However, it is not possible for the driving speed to drop below the minimum set speed.

Switch-on conditions for cruise-control system

–	The minimum speed of 30 km/h or 20 mph must be exceeded.
–	The brake pedal must be in rest position.
–	The clutch pedal must be in the rest position on vehicles with manual gearboxes.
–	Drive stage ”D” must be engaged on vehicles with automatic gearboxes.

Faults detected in the cruise-control system are stored in the fault code memory of the engine control unit. These fault code memory entries prevent any activation of the cruise-control system.

Conditions required for switching off the cruise-control system

–	Pressing the steering column lever upwards or downwards: switches off the cruise-control function.
–	Operating brake pedal
–	Operating clutch pedal (manual gearbox)
–	Engaging drive stages ”P” or ”N” (automatic)

 

 

Troubleshooting 

Cruise Control Not Working (Failure)

There are a few factors that will disable cruise control operations. 

Cruise Control Not Showing Speed

This can happen while coding on some cars.