Can't connect to ECU / DME with scantool

[BMW1999m3]

I have a '99 M3 and am trying to scan my check engine light codes. I cannot get either of my scan tools to establish communication. I have tried connecting my Carsoft scanner to the round 20-pin BMW port under the hood, as well as my Bosch generic OBD2 scantool to the OBD2 port under the driver footwell. Neither are able to connect with the engine computer.

The car still starts and runs fine. Why can't I connect? I have never had this problem before. I've checked the Motronic fuse 26 and it's fine(actually it still starts and runs even when I pull that fuse out). I don't believe there is a power issue to the diagnostic ports because both my scanners power up when they connect to each port, indicating they are receiving power through the port.

Are there any other fuses or relays that could be causing this? I've already tried disconnecting the battery for 30 minutes, and I pulled the ECU out and checked for corrosion on the pins, but everything looks fine.

Insight appreciated.

[BMW1999m3]

So I found out the problem. Apparently the underhood 20-pin connector lid needs to be on for my obd2 port to establish communication with my scantool. It looks like the lid has some pins and circuitry which is supposed to be connected to some of the connector prongs, and when it isn't the obd2 port goes null and cannot connect. I didn't realize this before, but upon reading the label on top of the 20pin lid, there is some sort of Dinan upgrade I did not know I had. Not sure if this has anything to do with it. I guess the previous owner installed it and I never bothered to read the label.

Anyway, once I reconnected the lid, my Bosch scanner on the obd2 port started working, and vice versa, my Carsoft started working when I disconnected the obd2 scanner. Weird!

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[gc325is]

Thanks for posting the fix.

[BMW1999m3]

Thanks for posting the fix.

For posterity

Just thought it was odd that it would do that and hope it will save anyone else time who can't get their scanner to connect. I'd be interested in knowing if this is just my car, or if other e36 owners have the same issue when they leave their 20-pin cap off.

[importbanana]

Why did this influence the ability to connect using the round port, which requires taking off the cap?

[BMW1999m3]

Why did this influence the ability to connect using the round port, which requires taking off the cap?

I just tried it again and now the 20pin round port Carsoft scanner connects fine, regardless of whether or not the OBD2 port scanner is connected. So I have no idea!! All I know for sure is the OBD2 port definitely doesn't work if the 20pin round port's cap is off(I think the little circuit board in the cap completes the circuit for the K-Line or something).

The other day I could not for the life of me get it to connect and then it just suddenly started working again for no apparent reason... I hate tech stuff sometimes.