Sort by Name Sort by Price

MS45 to MS43 ECU Conversion

If your car is a 2001-2002 330i/330ci, this page will not apply to you.

BMW used a Siemens engine computer, or engine control unit (ECU) to control the fuel injection system in the E46 model range. There were three versions for non-M cars: MS42 for 1999-2000 323i/328i, MS43 for 2001-2/2003* 325i/330i, and MS45 for 2/2003-2006 325i/330i. Another version was used on the M3 model (MSS54). The ECU is one component in the engine management for the car and is tied into other modules and systems.

* - 2003 model year. There was a period of six months from 9/2002-3/2003 where BMW mixed MS43 and MS45 components. Ignition coils, valve cover, and coil harness changed early (in 9/2002) but the ECU and engine harness remained MS43 until 2/2003. When searching for used MS43 parts make sure you specify a 2001-2002 330i to ensure the correct components.

Why Convert from One to Another?
For our purposes, we need to convert certain models to MS43 to meet the requirements in the Spec E46 racing class. As a spec class where all of the cars use the same equipment, it was decided that one ECU and one accepted tuned file (from Epic Motorsports) would be allowed. This reduces costs and eliminates complex differences between systems and any claimed advantages of one system over the other. For other tuning work MS43 may have some advantages as well (and vice versa) but we will not be addressing those here. Our focus is only on the Spec E46 racing class.

Parts Required
Backdating to MS43 requires more than just the ECU. The entire engine harness was changed with different connectors for various sensors and components. There are multiple ways to accomplish this conversion and we will outline a few here. Many of the parts required for a conversion can be purchased used, while some should only be bought new. For a complete and hassle-free conversion, the entire list from Option 1 should be completed.

Option 1: Complete Replacement
Most reliable and consistent for maintenance and parts ordering. This will convert everything to MS43 spec so it is the more expensive but least hassle option. Everything below is a direct bolt-on replacement and should be plug-and-play (see EWS section below). Therefore, it should be the most reliable as well with no wiring-related faults or failures. For parts purposes your engine will be the same as a 2001-2002 330i.

Complete Parts List:
- 2001-2002 E46 325i/330i main engine wiring harness (must be from E46)
- 2001-2002 MS43 Siemens ECU
- 2001-2002 ignition coils
- 2001-2002 ignition coil wiring harness
- 2001-2002 valve cover
- 2001-2002 intake air temperature sensor (the MS45 intake manifold is the same but a screw-on plug must be removed for this sensor)
- 2001-2002 voltage regulator or possibly the complete alternator
- 2001-2002 HFM/mass air sensor
- 2001-2002 pre-cat O2 sensors (post-cat sensors are deleted for Spec E46 racing)

Option 2: Partial Replacement with DIY Wiring
The differences in the valve cover and ignition coil harness appear to be minor. If you are comfortable with electrical wiring you can modify the MS45 coil harness (see image below). This will allow you to keep your MS45 valve cover, ignition coils, and the rest of your original harness (saving money). The downside is that you will have a mix of early and late parts that may be confusing when it comes time to order parts. And your wiring skills will dictate the reliability of your modification.

Option 2 Parts List:
- 2001-2002 E46 325i/330i main engine wiring harness (must be from E46)
- 2001-2002 MS43 Siemens ECU
- 2001-2002 intake air temperature sensor (the MS45 manifold is the same but a screw-on dummy plug is removed for this sensor)
- 2001-2002 voltage regulator or possibly the complete alternator
- 2001-2002 HFM/mass air sensor
- 2001-2002 pre-cat O2 sensors (post-cat sensors are deleted for Spec E46 racing)

The DME plug on the coil harness must be re-pinned to match the MS43 ECU. You can re-pin the existing plug or buy a new blank plug and the pins and start from scratch. In addition, a small change is required on the coil harness power/ground plug. The difference is shown in the image below. Unfortunately, BMW does not sell the MS43 plug by itself. We have identified similar plugs from the BMW catalog but your best option may be to change both harnesses to a more reliable design such as a Deutsch connector. You can also find specialists in the SE46 community who will build you a wiring harness to match your needs.

Overcoming EWS
You may finish connecting everything, turn the ignition key, and the engine only cranks without starting. The "likely" reason is caused by the EWS system. EWS is a sophisticated anti-theft system from BMW. The complete system consists of the ECU, an EWS module, the main body harness electrical module (GM5), the ignition switch and the key. All components are coded to each other and they must send coded messages to the ECU before it will allow the engine to start. The engine will not run if the ECU has been removed from one car and installed into another because the coding is not the same. You have two options to overcome this:

1. EWS-Delete Software. With the Spec E46 tune there is an option to remove the EWS requirement from the MS43 ECU. The ECU no longer looks for the signals from the rest of the EWS system. It just grants starting permission all the time. This is our preferred option for a lot of reasons: remove and simplify the wiring (deleting failure-prone EWS components as well), remove the key and use push-button start, keep a spare ECU, and swap ECU from one car to another. When you get your ECU back from Epic Motorsports, plug it and the engine should fire right up!

2. Factory EWS Alignment. BMW planned for issues like this and their factory diagnostic equipment has a feature that will align all of the codes from the car with the new ECU. This requires the rest of the EWS system to remain in place and be functional (EWS components are known to fail). The car must also be towed to a shop to connect to the diagnostic computer (unless your technician makes house calls). Most aftermarket diagnostic tools do not have a EWS alignment function. We are not in favor of keeping EWS for race cars so this option would rarely be advised.

Spec E46 Related Information
For Spec E46 racing the ECU must be shipped to Epic Motorsports for the flash software and series-required seal. We strongly advise adding the EWS-delete option with all Spec E46 software to eliminate the need for additional wiring or coding work.

If using a stock instrument cluster, additional wires will need to be added to your chassis harness to retain oil pressure warning lights. However, this will be unnecessary if a data acquisition system that accesses the CAN data, such as AiM, is used. Our experience is most racers are using such a system so additional wiring won't be required.

Wrapping Up
BimmerWorld can supply new versions of the complete list of conversion parts, but we encourage buying used when it makes sense. The ECU, wiring harness, and valve cover would be the limit of our recommendation typically. As with any used part, ensure they come from a running donor vehicle. And for any electrical part new or used, make sure you install it correctly and completely, as most electrical parts are non-returnable, and improper installation can damage or destroy them.

We do not provide installation assistance or guidance on this conversion. This tech article is intended as a guideline and gathering point for information. This page will change as new and better methods are worked out.

NEW MS43 Conversion Parts Available from BimmerWorld:

Main Engine Wiring Harness - 2001-2/2003 E46 325i/330i (MS43)

MS43 engine wiring harness. Genuine BMW part #12517513554.

Price: $427.77

View Product
Spec E46 Epic Tune ECU Small.JPG

Epic Motorsports Spec E46 Race Software (E46 330i)

Fully sealed and tamper-proof spec racing software for the Spec E46 class

Price: $599.00

View Product

Ignition Coil Pack, OEM - E36, E46, E39, E38, E31, X5, Z3

Replace your old and failing coils to optimize the health and performance of your engine

Price: $57.99

View Product

Ignition Coil Harness - 2001-2/2003 E46 325i/330i (MS43)

MS43 wiring harness for ignition coils. Genuine BMW part #12517551908.

Price: $189.99

View Product

Genuine BMW Valve Cover - E46, E39, X5, Z3

New valve cover with gasket to replace BMW part #11121432928

Price: $438.99

View Product
13 62 1 739 510 Air Temperature Sensor Small.JPG

Intake Air Temperature Sensor - E36, E46, E39, E38, X5, Z3

Sensor that provides the ECU with intake temp data. Replaces BMW part #13621739510.

Price: $15.99

View Product

HFM/Mass Air Sensor, VDO - E46 330i 01-03, E39 530i, E53 X5 3.0, Z3 3.0

OEM air flow sensor restores peak engine performance. Replacement for BMW part #13627567451

Price: $209.99

View Product

Pre-Cat Oxygen Sensor, Bosch - E46, E39, E38, X3, X5, Z3, Z4 (11781742050)

E46 325/330: -2/2003. OEM Bosch bank 1 or 2 pre-cat O2 sensor. 24 month warranty.

Price: $63.99

View Product

HFM/Mass Air Sensor, BMW - E46 330i 01-03, E39 530i, E53 X5 3.0, Z3 3.0

Genuine air flow sensor restores peak engine performance. Replacement for BMW part #13627567451

Price: $319.99

View Product
Sort by Name Sort by Price

What customers are saying...

  • I am extremely pleased with this order. The price was competitive and your expedited delivery charge was surprisingly low. I needed the part fast and you exceeded my expectations. I especially appreciate your gentleman who over the phone ensured me that the part was indeed in stock and would be shipped immediately.
    - Allan Read More
  • I’ve never dealt with a true “race” shop like BW and I really have enjoyed the experience. I always feel like I’m getting the best advice, and suggestions for true race car set up. Your technical expertise on even the minute details of building race cars is really impressive, and some I value greatly...
    - Paul Read More
  • I just can't express enough how impressed I am with you guys. Thanks so much for the great service from start to finish, and always done with a smile and as professional as possible. Our particular interaction has extended over many months and never have I felt that I wasn't getting first-class service...
    - Chris Read More
  • I just wanted to say what positive experiences I've had over the past few weeks. Your BimmerWorld sales staff have gone above and beyond to help me out, between their service and taking the time to answer all my questions, I'll be buying my parts from BimmerWorld whenever possible...
    - Aaron Read More