Coolant Pump Issues?

dnh325i · 01-15-2021, 08:47 AM

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?

MightyMouseTech · 01-15-2021, 09:06 AM

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.

dnh325i · 01-15-2021, 09:18 AM

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.

dnh325i · 01-15-2021, 09:21 AM

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.

MightyMouseTech · 01-15-2021, 09:48 AM

Quote:

Originally Posted by dnh325i

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.

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.

dnh325i · 01-15-2021, 10:47 AM

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?

MightyMouseTech · 01-15-2021, 11:11 AM

Quote:

Originally Posted by dnh325i

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?

Unfortunately, could be anywhere on the bus. First thing we always check though is at the water pump. With having the DME cover off in the rain though, I would be very thoroughly checking the bus connection to the DME. Can try unplugging it at the pump and see if it fixes the oil level sensor.

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.

Booda199 · 11-06-2022, 08:55 AM

Hello,

Did you ever find it out ?
My car is doing the same thing even after a new water pump and thermostat,,
With the same code 2acb only

Please help..

01-15-2021, 08:47 AM	#1
dnh325i Private 1 Rep 81 Posts Drives: '13 128i / Al Wht / Blk Lthr Join Date: Jul 2005 Location: Houston iTrader: (0)	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? __________________ 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
MightyMouseTech Major General 4338 Rep 6,196 Posts Drives: 13 135i 6MT LeMans Blue MSport Join Date: Feb 2013 Location: Ottawa, Canada iTrader: (0)	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
dnh325i Private 1 Rep 81 Posts Drives: '13 128i / Al Wht / Blk Lthr Join Date: Jul 2005 Location: Houston iTrader: (0)	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. __________________ 2006 E90 325i / Alpine White / Terra / Premium / Steptronic / Xenons / Fold down seats / No front license plate
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01-15-2021, 09:21 AM	#4
dnh325i Private 1 Rep 81 Posts Drives: '13 128i / Al Wht / Blk Lthr Join Date: Jul 2005 Location: Houston iTrader: (0)	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. __________________ 2006 E90 325i / Alpine White / Terra / Premium / Steptronic / Xenons / Fold down seats / No front license plate
	Appreciate 0 Quote

01-15-2021, 10:47 AM	#6
dnh325i Private 1 Rep 81 Posts Drives: '13 128i / Al Wht / Blk Lthr Join Date: Jul 2005 Location: Houston iTrader: (0)	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? __________________ 2006 E90 325i / Alpine White / Terra / Premium / Steptronic / Xenons / Fold down seats / No front license plate
	Appreciate 0 Quote

11-06-2022, 08:55 AM	#8
Booda199 Registered 0 Rep 2 Posts Drives: 650i F06 2013 Join Date: Nov 2022 Location: Kuwait iTrader: (0)	Hello, Did you ever find it out ? My car is doing the same thing even after a new water pump and thermostat,, With the same code 2acb only Please help..
	Appreciate 0 Quote