Replaced and programmed new ECU will not start

2006 BMW 525I
118,000 MILES • 3.0L • 6 CYL • 2WD • AUTOMATIC
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ALEXNILO710
  • MEMBER
  • 1 POST
I bought a new ECU for my car and had it programmed. But it wouldn’t start and I changed a few sensors and some relays and I had no luck it just cranks. I put in the old ECU and it started for like two seconds and continues to crank. Do I need the old ECU reprogrammed maybe?
Jun 30, 2019 at 9:03 PM
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KASEKENNY
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 18,907 POSTS
Hi Alex,

That is doubtful because once these modules are programmed they don't need to be reprogrammed unless there is an update. Rare case when a reprogram will fix an issue.

I would start with identifying why your engine is not starting. It needs three things to start. Compression, ignition at the correct timing, and fuel. I would assume that you have compression and the engine is timed properly due to it starting previously. That leaves spark and fuel. Try spraying some starting fluid down the intake and see if it starts for a second or two. If so, then we know we need fuel. If not, then pull a plug and keep it connected and hold it against the block and see if you have spark.

I suspect you don't have spark. If not, then we can go down the path of what is preventing your spark. Thanks
Jul 2, 2019 at 3:00 PM
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