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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E46 (1999 - 2006)

E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 11-21-2012, 08:30 PM
jinming jinming is offline
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Location: Maryland
 
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I'm getting a P0128 code

I got P0128 one month ago. Then I found the engine coolant level was low so that I refilled some coolant. Then the service engine soon light was off.

Yesterday the light was on again and I still got a P0128 code. I saw the coolant level decreased and refilled this morning. After drive several miles and re-start the vehicle, the light was off.

But tonight just before I arrived home, this light turned on again. It was really getting frustrated.

I leaned a few steps I showed follow:
Verify coolant strength & level
Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
If the above items check out good, replace the thermostat

But what should I do to verify the fan, ECT and IAT?
Can anyone help me on this?
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  #2  
Old 11-21-2012, 08:34 PM
QAfred QAfred is offline
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Did you look up what P0128 means? Typically that code coincides with a failed thermostat.
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  #3  
Old 11-21-2012, 08:42 PM
jinming jinming is offline
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Quote:
Originally Posted by QAfred View Post
Did you look up what P0128 means? Typically that code coincides with a failed thermostat.
Yes. it means: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

But I googled it and it may be other problems above.

So I should verified them before replace a thermostat.
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  #4  
Old 11-21-2012, 08:49 PM
QAfred QAfred is offline
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What car are you driving? Auto? Manual tranny?

Your electric cooling fan you can simply observe if it turns on after car is hot, park, pop the hood and it should be running or start running after sitting a minute.
ECT is on the bottom rad hose and you would have a bad temp indication or none at all if it failed
IAT wold cause erratic idle if it failed, it is a sensor in the top of your intake

thermstats fail regularly on these vehicles, the others rarely do.

You also need to consider cooling system overhaul (Water pump, thermostat, expansion tank) you water pump may be what is leaking.
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Old 11-21-2012, 09:09 PM
jinming jinming is offline
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Thanks a lot.
But how to check if the water pump is leaking?
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  #6  
Old 11-21-2012, 09:19 PM
BMW318i_E36 BMW318i_E36 is offline
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I got that code with the engine light last weekend, went to my mechanic and he cleared it, and it hasn't come back since.
I had my car parked for 15 minutes today with the engine on, the fan attached to the water pump worked but the fan after radiator, never came on.
Could I have a problem?
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  #7  
Old 11-21-2012, 09:21 PM
QAfred QAfred is offline
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When you take it all apart to get the thermostat out, it is only four nuts to remove water pump too. Simply DIY. It should be evident what is leaking once you start inspecting. Expansion tanks, Radiators, and water pumps are typical leakers on these cars.

If the WP is leaking it will obviously be wet behind the pulley that covers it. If it is very slight, you will notice white spots where the antifreeze has dried up.

Again, what kind of car, how many miles? automatic or manual, Do you know the maintenance history etc?
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Old 11-21-2012, 10:08 PM
jinming jinming is offline
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Its a 2004 BMW325xi, Auto, 61000mile.

I brought from a dealer two months ago. I'm not sure the maintenance history but I did the 6mile inspection in BMW dealer. A "power steering hose from the pump to the rack leaking" reported. Nothing else.

I will try those inspections of water pump tomorrow.

Thank you very much.
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  #9  
Old 11-21-2012, 11:02 PM
QAfred QAfred is offline
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Okay, I would definitely change the faulty thermostat, WP and Expansion Tank while I was at it. If the date on the upper and lower rad hose is 2004, you should change them too. Here is a couple good links:

http://www.oembimmerparts.com/BMW_E4...s_s/1863.htmk:
http://www.pelicanparts.com/bmw/cata..._pg1.htm#item4

The GRAF is a good WP and only $44

Last edited by QAfred; 11-21-2012 at 11:04 PM.
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