I need to disconnect the battery, but don't want to reset the ecu. last time I took of the ground for about a minute, the ecu didn't clear, and my radio stations stayed set, although the clock did. so, do these systems have a backup or something, or will I loose the data after prolonged battery disconnect?

 

You will most likely lose the data. It is possible for residual power to be retained temporarily in capacitors in some of the electronics, but if you disconnect power for more than a few seconds you will probably reset everything.

Remember too that major fault code (can't remember the proper technical term) DTC's won't reset with disconnecting the power no matter how long you disconnect it. They require a scan tool to clear.

 

yep the ecu reset after I had the battery out for a couple of hours, but my radio presets stayed in. it sucks, because I've been trying so hard to get the evap test to complete. but if I'm lucky I fixed the secondary air problem, and just need to wake up early enough to do a cold start, and run the test (even in the spring in Las Vegas it won't run during the day). the smog test will ignore one incomplete test.

 

The radio will retain set stations for a couple of days with no power via a capacitor in the radio.
The ECM has no internal battery, but the DTC codes remain in memory (static memory, not dynamic) until cleared via a scan tool.

 

I didn't have any fault codes,to loose but I did loose the drive cycle data.