So, the battery in my '06 xB (220000 miles manual) died and to get home I decided to push start it. When I popped the clutch there was a "thunk" when it started that I'd never heard before. All the dash lights came on, the radio turned off, but the engine sounded fine. I decided to drive it home rather than wait for a tow. It drove, but was periodically hesitating, like it might stall, but always recovered. I got home okay, but now need to figure out where to go now. There were no Codes when I checked Besides a new battery, I'm thinking I probably fried the ECU. Does that sound plausible? If I can find a junkyard ECU, does it need to come from a manual transmission car, or are they all the same?

Any thoughts?

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I'd put the new battery in and see if that helps...a low battery will cause all kinds of issues in newer cars and push starting likely didn't fry your ECU. If it had you wouldn't have been driving it home.

 

Also test alternator to make sure it's working to charge battery. Otherwise your new battery will soon be dead as well.

 

I'm pretty shocked, but you're spot on. It was in fact just the battery! I've never seen a bad battery throw the dash so out of whack! I thought for sure I must have fried some sort of control circuit. Thanks for your help 👍

 

A quick alternator check would be to measure the voltage at the battery with the engine running. At 2000 rpm you should see about 14V

 

This is extremely common on newer vehicles. Low voltage creates all kinds of random issues.

 

Battery is only used to start engine.

After that it's alternator that provides ALL power to operate engine and recharge battery. If you're not getting sufficient power to operate engine properly as well as charge up battery, then alternator is suspect.

Even bad battery will not cause car to run poorly.