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01-15-2021, 08:47 AM | #1 |
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Coolant Pump Issues?
Background: I've owned this E82 128i for five years, and 100K miles. Currently 125K. Mostly trouble free, great, fun car. I have flushed/changed the coolant once that I recall. Over the holidays, I decided to do the valve cover gasket as it had begun leaking and creating a smell in the cabin.
That was done without a hitch, except: When I reconnected the battery, the car started right up, and ran great, drove to the grocery store, came home, all good. Then the car was parked for a few days, and next time I got in the battery was dead. New battery, and now the water pump runs and will not shut off. Limp mode symbol is on, service engine soon light is on (but the car starts and drives fine), and I can't clear these out with my analyzer. DME relay code is active (2ACB). Questions: 1. What is the logic that causes the water pump to run? Of course, high engine temp, but where is that logic housed? In the pump itself, or the DME? 2. How is power distributed to the pump motor? Through the DME relay? Could that be the cause of the issue or somewhere else? During the VCG change, the lid needs to come off the DME junction box, and that was off for a couple of days, while I waited out a rain storm. I'm ready to pull the water pump/thermostat, and replace it, as it has never been replaced, but will this solve my problem?
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2006 E90 325i / Alpine White / Terra / Premium / Steptronic / Xenons / Fold down seats / No front license plate
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01-15-2021, 09:06 AM | #2 |
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If the pump looses communication, it will run all the time, which will kill the battery. Did any water get the DME box? I would be checking all the connections in there first.
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01-15-2021, 09:18 AM | #3 |
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That's good info, thanks MightyMouse. The harness that goes down to the pump contains a bundle for the pump (four wires?) and a two wire plug connection to the thermostat, correct? I actually design and build motor control systems on a much larger industrial scale, so I have some background in how these systems think and react. Trying to apply that thought process here.
I shut the hood, and tried to cover everything up good for the rain, and there is no sign of water in the box. I pulled the cover off again to check this specifically. Nothing seems amiss inside there.
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01-15-2021, 09:21 AM | #4 |
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It'd be awesome if someone had a cause & effects diagram for the E8X/E9X N52 engine system, along with a controls narrative. In English.
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01-15-2021, 09:48 AM | #5 |
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The alternator, oil level sensor and water pump are all on the same LIN bus connected to the DME. See if you can check your oil level? Any coolant in that bus connection at the pump will short the bus to ground and all three items will loose communication. When the pump looses comms, it runs full time. When the alternator looses comms, it will continuously charge at 14.4. When the oil level sensor looses comms, it just does not work.
Last edited by MightyMouseTech; 01-15-2021 at 10:26 AM.. |
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01-15-2021, 10:47 AM | #6 |
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Very good, another piece to the puzzle. I do not have the oil level sensor available either. It shows an error when I check the oil level while driving. So most likely, a short at the coolant pump, repaired by changing the coolant pump? This is where I was headed any way, so you are confirming my original suspicion. Any chance that short is at the other end of the harness?
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01-15-2021, 11:11 AM | #7 | |
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Quote:
That's one nice thing about a simple LIN bus. If it is a bad component on the bus, as soon as you disconnect it, the other items on the bus will come back. |
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