Known Issues Inquiry - Swapping MSS54 to MSS54HP and Back for Smog

[AWE46M3]

Hello Group,

For the benefit of the pre-LCI E46 M3 owners, I am hoping to document the known issues when swapping from an MSS54 to MSS54HP DME's and back for smog checks. If you go back to stock and swap DME's between smog checks, please let me know of any issues you've encountered so I can consolidate a list of things to be aware of for future reference.

I have questions below that I will update into notes once I receive answers to clarify additional details and considerations for the topic.

Issues List:

1. DME / EWS syncing is required between swaps. The EWS will pick up the change between miles since the last time the car was operated with the stock DME and lock the car out resulting in a no start/no crank. EWS can be deleted on HP DME if desired. EWS must remain enabled on the DME used for smog.


2. Coolant temps going into the red due to software version mismatch.
Note: rare issue. Can be fixed by installing the compatible software version. Verify with tuner.


3. Program new HP DME to match mileage and VIN with the LCM
Note: Worth doing while you're at it to prevent a tamper dot, but may not be essential.


4. Complete drive cycle to activate emissions monitors (see post Albums for additional details).


Please let me know if anything else should be added to this list. Thanks in advance for your collaboration and contribution. I'll be honest - the airbox is the one mod I'm the most excited about and also dreading due to all of its nuances and considerations.

[bmwfnatic]

I was going to reply to this yesterday but didn’t get around to, but here you go.

Miles do not matter, your EWS from factory contains a rolling code table, which is a big table of random codes that must match in the DME and EWS for the car to start, it starts at code 1, then next start code 2 then code 3 and so on, until it gets to the end of the table and eventually wraps around to 1.

A virgin DME will have an empty EWS table, and will be able copy the table from the EWS only on the first start.

Re-syncing the EWS in essence tells the DME and EWS to both start at code 1 again, this is useful if you used another DME, but the DME you are syncing must still already belong to the car.

While I am not familiar with California Smog, your source and also some material on this forum states they are using a checksum, which means that even a single byte changed in the tune area will cause the checksum to change and it can know the software has been altered, EWS delete would obviously change data in the tune area and is therefore not viable, but not really necessary either.

The coolant temps going into the red is just a mistake made by people caused by flashing a tune that is meant for the wrong software version to the DME, the DME has no clue what to do if that happens and the temperature meter is its designed way to let the user know.

I don’t think you need to match mileage and VIN against the LCM, I am not even sure if the DME carries mileage at all, it does contain a VIN, but that’s trivial.

—————————————

If I were in your shoes, I would keep my stock unmodified ECU, store it somewhere safe.
Get a separate HP ECU, if you are doing the CSL software on it, it will end up as a virgin anyway and it’ll pair with your EWS, run it, have fun.
When the time comes to swap back, put your stock ECU in, do the EWS re-sync procedure to align your rolling code again and you are done.

[zzyzx85]

I typically run a tuned HP DME for my air intake box but swap back to my OE non-HP DME and stock airbox/air intake system when it comes time for smog.

OE DME is untouched. HP DME has been tuned by Kassel with EWS delete.

1. EWS sync-ing - When I go from HP to OE DME, it typically takes a few tries to sync the EWS using INPA but eventually it sorts itself out.
2. I've never had that issue.
3. I provided Kassel my VIN when they programmed the DME but I did not need to provide my mileage.

I also swap back the pin at the ECU (I believe its for the IAT).

[Epsilon]

I was going to reply to this yesterday but didn’t get around to, but here you go.

Miles do not matter, your EWS from factory contains a rolling code table, which is a big table of random codes that must match in the DME and EWS for the car to start, it starts at code 1, then next start code 2 then code 3 and so on, until it gets to the end of the table and eventually wraps around to 1.

A virgin DME will have an empty EWS table, and will be able copy the table from the EWS only on the first start.

Re-syncing the EWS in essence tells the DME and EWS to both start at code 1 again, this is useful if you used another DME, but the DME you are syncing must still already belong to the car.

While I am not familiar with California Smog, your source and also some material on this forum states they are using a checksum, which means that even a single byte changed in the tune area will cause the checksum to change and it can know the software has been altered, EWS delete would obviously change data in the tune area and is therefore not viable, but not really necessary either.

The coolant temps going into the red is just a mistake made by people caused by flashing a tune that is meant for the wrong software version to the DME, the DME has no clue what to do if that happens and the temperature meter is its designed way to let the user know.

I don’t think you need to match mileage and VIN against the LCM, I am not even sure if the DME carries mileage at all, it does contain a VIN, but that’s trivial.

If you physically remove the stock OEM DME and EWS module together and then put them back for smog at a later time, do they need to be re-sync'ed again?

Also, if you disable EWS on the DME, does the physical EWS module need to be present?

[bmwfnatic]

If you physically remove the stock OEM DME and EWS module together and then put them back for smog at a later time, do they need to be re-sync'ed again?

Also, if you disable EWS on the DME, does the physical EWS module need to be present?

In theory if you remove both then yes, they should stay synced.

Yes, “disabling EWS” is done on the DME, in essence it allows you to start the car with a DME that does not belong to the car, that’s all it is, it doesn’t remove the need for or entirely bypass the EWS module.

You won’t be able to say, start the car with a screwdriver in the ignition, the EWS module will still look for the transponder in your key, and ultimately control the starter. In order for you to remove the EWS module completely you would have to re-create that aspect to control the starter via a relay based off the signal from the ignition being in the crank position.

[AWE46M3]

bmwfnatic - thank you for kicking the thread off - I appreciate you taking the time to send over those details. Very helpful!

zzyzx85 - Glad to have a reference for someone who has gone back and forth with 2 different DME's. Thank you for your feedback 🤝

Epsilon - I had the same question - that's good to know.


Appreciate you all for contributing to the discussion. I'll add to the list if I find any other gremlins worth noting. It seems like the DME and the EWS playing nice is the key to success for the swap. #2, the overheating issue, seems to be pretty rare.

[TheElite///M3]

So when you swap DME do you leave your CSL airbox and the. Smog? Thanks in advance, I too am from cali and was going to just HTE tune and save my stock dme as noted above

[AWE46M3]

So when you swap DME do you leave your CSL airbox and the. Smog? Thanks in advance, I too am from cali and was going to just HTE tune and save my stock dme as noted above

No, go back to stock airbox. Completely revert to stock. Car won’t run right with a stock tune + CSL airbox.

[Epsilon]

Here's another tidbit: If you swap back the stock DME, you have to perform the drive cycle to get the monitors ready before SMOG.

[AWE46M3]

Here's another tidbit: If you swap back the stock DME, you have to perform the drive cycle to get the monitors ready before SMOG.

haha! that goes without saying, but appreciate you mentioning it. I'll add it to the list. Graphic for drive cycle in case someone is researching and wants this for reference.

[Casa de Mesa]

Hey man. Saw the Bat signal go up. I'm afraid I'm not much help here. In NC, smog/emissions isn't a thing after the car hits 20 years old. So literally the only thing the car needs is a safety inspection. I've been rocking the CSL computer as I didn't have a need to swap it out...

[AWE46M3]

Hey man. Saw the Bat signal go up. I'm afraid I'm not much help here. In NC, smog/emissions isn't a thing after the car hits 20 years old. So literally the only thing the car needs is a safety inspection. I've been rocking the CSL computer as I didn't have a need to swap it out...

Nice!! Glad to hear it. Thanks for chiming in anyway. Hope all is well