mikey72378

So it all started with a check engine light and "Increased Emission" message. I took my 545i to the stealer, since I have a limited extended warranty that may or may not have covered the issue. The dealer called and told me that I had a bad thermostat, which was not covered by my extended warranty. Since they wanted $525 to replace it, I opted to change it my self. I ordered a Beck Arnley 143-0869 thermostat and installed it. The code did not clear and my heater still did not work. I then replaced the coolant temp sensor right after the thermostat, which did not fix it either. I thought maybe the new thermostat was faulty so I exchanged it for the same kind and replaced it again, which was not the problem. At this point the car is drivable, but its cold even here in Texas, without a heater. The P0128 code is still active as well. Im just wondering what direction to go from here. Any suggestions would be greatly appreciated. I have searched past threads, but have not found a solution.

mikey72378

Two things I forgot to mention, the fan is not running excessively and the coolant level was topped off. Also I have 75K miles on the car.

e6t.lab.rat

I too have the SES light, P0128 code as well on my '05 545. I've read on here a thread saying the resistance on our thermo between the two contact leads should be around ~16 ohms (closed/cold). Well, I measured mine and got ~15.xx so I'm assuming my thermo should be good.

I do know that the sensor on the lower radiator hose activates the fan for cooling demands. The upper sensor (closest to and before thermo - I'm guessing you changed this out) gathers coolant temp from engine and when too hot, it will usually indicate a bad thermostat. But sounds to me that the latter part you attempted did not solve your problem. I also thought about changing out my upper sensor in the hopes it'll clear my SES light but now I'm having doubts it'll work. Well, it's cheaper than the thermo so I may as well. I'll check back later with results when done. Try bleeding the coolant system of air. Good luck

BimmerFan52

For code P0128, the engine's PCM detected that the engine has not reached the computer mapped temperature level within a certain time after starting the engine, taking into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.
The intent of the P0128 code generally is to indicate a faulty thermostat, but code P0128 may also mean that one or more of the following has happened:

• Low engine coolant level
• Leaking or stuck open thermostat (not this since you have swapped out)
• Faulty cooling fan (running too much)
• Faulty coolant temperature (ECT) sensor
• Faulty intake air temperature (IAT) sensor

Some additional thing to check when troubleshooting and repairing a P0128 OBD-II code:

• 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.

camshaft

I have been through 2 of these beck arnley thermostats. The thermostat is actually fine, however the sensors go bad on them. I a toying with the idea of closing the thermostat sensor circuit with a paper clip and resetting the code. I'll let you know how that goes. 2 thermostats in 5 months.

BimmerFan52

That was my experience also. The mechanical portion of the thermostat (spring, plunger and wax) worked fine. Just the heater coil had burned out.

I didn't give B&A a second chance - I threw in the towel and ordered an OE Wahler and it hasn't made a peep in 9 months now.