how to HARD RESET the DME?

[Jason C SBB]

If I clear the codes in the DME using my Actron code reader, it still remembers the "hidden" codes and the long term fuel trims.

I tried disconnecting the battery for 20 mins, no difference.

How do I do a "hard reset" on the DME so that it forgets long term fuel trims, etc, and the "hidden" codes?

[thejlevie]

OBD I or OBD II car (i.e., pre/post 1996)? A reset of the fuel adaptation values and clearing of pending codes requires a full-up BMW specific diag system, like your dealer or well equipped BMW indie would have. As far as I know, a generic OBD II tool can't do it.

[Jason C SBB]

Obd2.

So when I left the battery disconnected for 6 months while it waited for a new head, that didn't hard-reset it?

[united323is]

You could try doing a battery reset. disconnect the negative cable from the negative post then contact it to the positive. It may briefly spark, but its okay. leave it like that for 30 seconds. then leave the battery disconnected for 15 minutes. grounding the positive terminal will discharge all the capacitors in the vehicle. allowing the vehicle to forget many things. It may work for the codes, I have not tried, and I know it doesn't work on the new cars.

[M///BMW]

You could try doing a battery reset. disconnect the negative cable from the negative post then contact it to the positive. It may briefly spark, but its okay. leave it like that for 30 seconds. then leave the battery disconnected for 15 minutes. grounding the positive terminal will discharge all the capacitors in the vehicle. allowing the vehicle to forget many things. It may work for the codes, I have not tried, and I know it doesn't work on the new cars.

seriously.. that sounds like some of the worst advice ever LOL!

[downeaster1]

You could try doing a battery reset. disconnect the negative cable from the negative post then contact it to the positive. It may briefly spark, but its okay. leave it like that for 30 seconds. then leave the battery disconnected for 15 minutes. grounding the positive terminal will discharge all the capacitors in the vehicle. allowing the vehicle to forget many things. It may work for the codes, I have not tried, and I know it doesn't work on the new cars.

WTF?? DON'T DO THAT!!?!?!
I've read enough horror stories about people frying so many things in their car by accidentally putting the battery terminals on backwards. No good could possibly come out of that.

[easymoney]

You could try doing a battery reset. disconnect the negative cable from the negative post then contact it to the positive. It may briefly spark, but its okay. leave it like that for 30 seconds. then leave the battery disconnected for 15 minutes. grounding the positive terminal will discharge all the capacitors in the vehicle. allowing the vehicle to forget many things. It may work for the codes, I have not tried, and I know it doesn't work on the new cars.

Oh my good lord!! You may fry a lot of shit in your system doing that crap! I will never try doing that in my car, never, ever! Amen.

[Brent 930]

Hold on for a moment. Ultimately he is saying the neg. terminal of the battery is floating, or not connected when touching the positive lead. There is now no return for current to flow. I would get a meter and check the voltage between the pos. and chassis.

If there is any voltage after 5 min. then instead of shunting the floating pos. ternimal to chassis, you could take a 10K resistor from the pos. to chassis and bleed it down. Unless you have a booming stero with big capacitors it will probably be zero. Otherwise after 15 sec. go ahead and re measure the voltage. It should be zero or very close to it. Once this measurement is at dead zero you can then be sure this is the best reset you can do.

[thejlevie]

I don;t know if it universally true, but I think that the data storage in an OBD II BMW is in non-volatile memory. In which case only a diag system can change that data.

[ScotcH]

I don;t know if it universally true, but I think that the data storage in an OBD II BMW is in non-volatile memory. In which case only a diag system can change that data.

Yup. You need a diagnostic tool to pull and reset the codes

[Jason C SBB]

So I took the negative cable off, and shorted it to the positive terminal. A huge spark ensued, and a small fire. Good thing I had a fire extinguisher! I reconnected it, and the car wouldn't start. I had the car rtowed to the dealer, and I need a new DME - $1,200. No more CEL!!! Hooray!!!

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LOL. Just kidding. I left the battery off overnight and the CEL greeted me in the morning.

Again as I said, my Actron isn't capable of resetting the long term fuel trim and "hidden" codes.

[Ace M3]

If you're OBDII, you need a tool. No way around it.

On my OBD1, I disconnected the battery and took out my DME, replaced the chip, and everything was reset.

I like.

[moneydump]

Oh my good lord!! You may fry a lot of shit in your system doing that crap! I will never try doing that in my car, never, ever! Amen.

This is an old post however the pos cable to earth is called latching....afterwards strart car...if not start immed..leave w/ ign on for 2-3 min as ecu is in an anti scan mode...immediate start or not when the engine starts DO NOT TOUCH THROTTLE UNTIL COOLING FAN KICKS>>>(cannot stress this enough)..then drive for 10 min + touching 4k rpm in all gears....you're welcome

[pbonsalb]

Won’t do anything for obd2. Buy a tool that can reset adaptions.

[TostitoBandito]

FWIW most/all software flashes will reset all that stuff. So if you've been wanting to get a tune, or you have a tune and can flash back to stock and then back to your tune, that will likely take care of it.