Intermittent P0128 After Switching to 88-Degree Thermostat

[BMW540san]

Peter,

I'm almost certain that you have no air in the cooling system, especially if you monitor your KTMP and it stays steady, no temp varying down or up quickly.

I know for certain that there is no set number of days or miles for monitors to get ready. About couple months ago, I had issue with 540 where I had to reset all of them and even though I did number of drive cycles, it took about a week. I was watching them every day and they were going out randomly.

If you decide to go back to old thermostat, you only need to drain radiator.

I'm really puzzled with your issue and I truly hope you get it resolved.

[peter540]

Not sure what version of the DME firmware I have. How can I find out? Do I use the VIN? My car's an '03, built in Nov. '02, I think. And I have no idea how to go about reflashing the DME, either. How is that accomplished? Bear in mind I don't have anything other than a generic code reader. No INPA or anything.

I'm running a BMW OEM 88° thermo right now. I haven't added a resistor yet, and I'm somewhat hesitant to do that if I have to revert to the original thermo to pass emissions.

My registration must be renewed by March 1st; I'm at the edge of not being able to legally drive the car.

[ninetyseven1]

it's none of emissions business if you have a cel or not , those guys have no knowledge of how your dme functions anyway lol, I doubt you need a reflash just use the resistor we all mentioned and you will be fine, clear any check engine light before emissions and you will be fine also, the lower temp thermo should not effect your exhaust emissions too much really, usually lower temps result in richer mixtures but 88c is plenty hot enough . Most cars don't even run that hot. you should be fine , adding a resistor won't hurt anything, don't be afraid of this car. It's a quite simple dme , not even as advanced as my 1991 GM Firebird

[BMW540san]

it's none of emissions business if you have a cel or not , those guys have no knowledge of how your dme functions anyway lol, I doubt you need a reflash just use the resistor we all mentioned and you will be fine, clear any check engine light before emissions and you will be fine also, the lower temp thermo should not effect your exhaust emissions too much really, usually lower temps result in richer mixtures but 88c is plenty hot enough . Most cars don't even run that hot. you should be fine , adding a resistor won't hurt anything, don't be afraid of this car. It's a quite simple dme , not even as advanced as my 1991 GM Firebird

My only goal here is to help Peter not to compete in knowledge but I have to correct you here.
Here is official explanation from his own state what can cause monitors not to be ready and basically pretty much everything is emission related including the coolant temp:
So your statement: "it's none emissions business if you have cel or not" is totally false.
A qoute from link below: "If the “Check Engine” or “Service Engine Soon” light is on, a vehicle will not pass the inspection"
http://www.cleanairforce.com/motoris...-testing-2015/
I've been wrong many times as well so I'm just correcting here, not playing "who's smarter" game.

[peter540]

it's none of emissions business if you have a cel or not , those guys have no knowledge of how your dme functions anyway lol, I doubt you need a reflash just use the resistor we all mentioned and you will be fine, clear any check engine light before emissions and you will be fine also, the lower temp thermo should not effect your exhaust emissions too much really, usually lower temps result in richer mixtures but 88c is plenty hot enough . Most cars don't even run that hot. you should be fine , adding a resistor won't hurt anything, don't be afraid of this car. It's a quite simple dme , not even as advanced as my 1991 GM Firebird

Actually, that's incorrect. All the monitors in the DME must be in a state of "readiness," or the emissions computer won't pass the car. If the check engine light is on, that also means some monitor or another is not in a state of readiness, and the car won't pass, period.

As for the resistor, the majority of people seem to say the resistor won't have any impact on the P0128 code. How many of you would agree the resistor is likely to resolve this issue? If most agree, I'll add the resistor ASAP.

In the meantime, I'll continue to monitor the KTMP. Seems strange that the code always his as the last monitor (oxygen sensor-related) is about to become ready.

[mandd]

My only goal here is to help Peter not to compete in knowledge but I have to correct you here.
Here is official explanation from his own state what can cause monitors not to be ready and basically pretty much everything is emission related including the coolant temp:
So your statement: "it's none emissions business if you have cel or not" is totally false.
A qoute from link below: "If the “Check Engine” or “Service Engine Soon” light is on, a vehicle will not pass the inspection"
http://www.cleanairforce.com/motoris...-testing-2015/
I've been wrong many times as well so I'm just correcting here, not playing "who's smarter" game.

You are 100% correct.

it's none of emissions business if you have a cel or not , those guys have no knowledge of how your dme functions anyway lol, I doubt you need a reflash just use the resistor we all mentioned and you will be fine, clear any check engine light before emissions and you will be fine also, the lower temp thermo should not effect your exhaust emissions too much really, usually lower temps result in richer mixtures but 88c is plenty hot enough . Most cars don't even run that hot. you should be fine , adding a resistor won't hurt anything, don't be afraid of this car. It's a quite simple dme , not even as advanced as my 1991 GM Firebird

This is a false statement It is much more advanced than your 91 GM Firebird. The engine is required to be at an optimum temperature to run efficiently, I do not think anyone here is a BMW Engineer. The monitors rely on engine temperature has well to carry out the required test run such has Secondary Air, Evaporative Emissions, O2 Sensor and Catalyst. You may never set the O2 monitor if the engine temperature never gets into the plausible range, conversely if this plausibility occurs then it may set an erroneous coolant temperature regulation fault.

If you clear the check engine light just before your E test you will fail because your monitors will not be ready.

To Peter540 re-flashing the DME will have no effect, if so determined then fit the resistor and clear the faults. Then carry out your drive cycle(s) set the monitors and get the E Test. By looking at the monitors on the screen there is no way to tell if the monitor is about to be "Ready", you will need to go into Mode$05 and Mode $06 to check this parameter.

Mark.

[philly98540]

His ktemp seems on target with whats expected and what others are getting. The code he gets is not the code that gets fixed with adding the resistor. I'm thinking there must be some variable in the DME that compares KTEMP to expected KTEMP. There may be some variance between cars with this variable. This makes some cars get a code if the engine is below expected temp. I'm speculating of course here. Maybe someone like DUDMD may know. If this variable does exist, it could be altered to eliminate the code. Not sure why BMW would have different setting for this variable, but we have seen some cars get away without the resistor, whole some need it. So we know there are variances even between the same type of engine/DME config.

[Da Beemers]

It's a quite simple dme , not even as advanced as my 1991 GM Firebird

That is flat out ridiculous, or one very special Firebird.

If you do install the old thermostat there is no need to drain the radiator. When Installing mine I held the hose up to the side while installing and only lost maybe a cup of coolant, which was put right back in from the pan I had under the car. I did not have to bleed or add any other coolant. As far as the resistor, I don't think it has anything to do with the readiness state. Many of us have been running this thermo with no resistor and have no trouble, code, or light.

[JimLev]

You could always disconnect your Zionsville electric fan and maybe block off part of the radiator with a piece of cardboard to get the temp up just for passing inspection, then you'll have time to mess around with it later.
Yes, I'd install the resistor just to rule out that it MAY have something to do with your CEL.
You could always just take your old t-stat and lay in under the top engine cover with the connector plugged into it, leaving your 88°C t-stat installed.

[ninetyseven1]

I'm s professional tuner of GM cars and have owned several 540is , if temperature is effecting the emissins you can install a manual switch on your electric fan and turn fan off to get temps up and fuel
Trims to rise which results in a leaner mix. Depends in why your failing emissions , I had high HC (too rich)on my 540i and only running one cat converter too and I made the car pass by raising temperature, a bottle
Of heet in the gas tank helps too! Heet is alcohol

[ninetyseven1]

Point is , thermostat change will not cause the car to fail emissions, I use a thermo from a 840ci and its a direct bolt in . never had an issue with emissions due to temps or a thermostat. just put a resisitor
In . 100 watt 12 ohm , they are like under $10. https://www.walmart.com/ip/100W-Watt...istor/45612413

[ninetyseven1]

There is no
Readiness to worry about , nobody pays attention to that , as long as you have no cel your car is ok , but if you want to see the real errors you don't want to use INPA , Inpa is only good for checking cel codes, monitoring auto Trans temp while filling it, and for looking up software versions , you want to use PA soft 1.4 the rest of that software out there is garbage and unconvenient!

[peter540]

Jim has an interesting idea of plugging in the original thermostat while the 88° one's in there. I'll try that, finding a good spot where it can sit. Part of me still thinks that, given how sophisticated the technology is in these cars, that there's enough logic in the system that if the connection is lost to the thermostat heater, which happens without a resistor being added with the 88° thermostat, it might sense the break in the chain.

I'll also disconnect the ZV fan, which will come on at the lower speed when the KTMP is around 93. I should note that when the fan is on, no SES or codes occur.

BTW, for those who DID get a code prior to installing the resistor, what code was it?

As for passing emissions, it can be the case, as it was with me, that no code is present, but one or more monitors are not yet ready. The emissions facility's computer can see this and will fail the car. It happened with my car. Once the check engine light is on, they flat out will not pass the car, in part because some monitor will not be ready.

[ninetyseven1]

I don't think our cars are very complicated at all when it comes to dme , my GM Firebird had much more options and parameters to be changed in the tune compared to the 540i, ignore the word readiness , nobody worries about that , there things called shadow codes
Which you would worry about but as long as you have no cel , nothing to worry about , in fact not using a
Resisitor should NOT set off a cel it does set an error though

[ninetyseven1]

I hade owned three 1997 540is with a resistor installed and not once did
I ever get a cel but I got an error which u can see using correct software like
Bmw scanner aka pa soft . Inpa is pia and will not show errors like this

[peter540]

Are you saying that when the original thermostat is removed from the circuit, it doesn't throw a code, but it does generate an error, but that error doesn't show up as a P-code or trip the SES?

[ninetyseven1]

Sounds like you may have a bad thermostat , is the lower hose getting warm like it should ? try re- bleeding the system by squeezing he hoses , that's all
You need to do to bleed our cars, and make sure the red bobber in the expansion tank is about an inch below the hole, you don't want to overfill our cars

- - - Updated - - -

Are you saying that when the original thermostat is removed from the circuit, it doesn't throw a code, but it does generate an error, but that error doesn't show up as a P-code or trip the SES?

it does not set off the CEL , it's an error , if you run Pa soft in your car you will prob find at least 30
Errors, most

- - - Updated - - -

It has nothing to do with the thermostat it its temp rating man ,the error you get has to do with the fact that there is no resistor in place, basically at certain times and also when u go full throttle the dme sends 12 v through those wires to the heater on your stat. If there is no heater present you need a resistor in place . The code p0128 I don't believe to be related
To these wires though.

[peter540]

Due to the urgency of my need to clear emissions in the next week, I think I'll revert to the original TSTAT; I only have five days, or one drive cycle, left. Once I pass emissions, then I can mess with the 88° TSTAT.

[JimLev]

Peter, the car that nintyseven1 is talking about has a different DME than your '03 DME.
So it's apples to oranges, just try what I said above and see what you get for results.

[peter540]

Peter, the car that nintyseven1 is talking about has a different DME than your '03 DME.
So it's apples to oranges, just try what I said above and see what you get for results.

Just worried that I don't have enough time left to try your method; if it doesn't work, I can't get my car through emissions and registered. I'll try your idea after the car's made it through emissions.

[DUDMD]

I can change the thermostat maps to lower the expected temps, but easier to just delete the fault codes permanently from the DME and not worry about it.
I can delete them as well.

[peter540]

I can change the thermostat maps to lower the expected temps, but easier to just delete the fault codes permanently from the DME and not worry about it.
I can delete them as well.

Thanks, DUDMD. I've PMed you.

Today, I got a 30-day extension to complete the car's emissions, so I decided to try Jim's suggestion -- leave the 88° thermostat installed, plug in the old thermostat, essentially using it as a form of resistor, and unplug the Zionsville e-fan. I've done all that, and with temps in the low 50s, I observed that it takes longer than expected for the car to get up to operating temp (90°+). Is that normal? Once warm, the KTMP continues to range between 90-94°. I assume it is.

Would someone please give me a 101/beginner education on the purpose of the original thermostat's heater? What is its purpose? When is it supposed to be activated? What does the thermostat do when the heater is activated? My assumption is that the heater comes on when the engine is cold, but I have NO knowledge of how this thermostat works.

Thoughts?

--Peter

[philly98540]

The thermostat heater is only activated at times of extended full throttle or if the engine Temps go above like 118 C or something close to that. I forget. The heater lowers the stat control temp to 83 C or thereabouts. So, for all normal driving situations, it does nothing and the stat behaves like any normal single set point mechanical stat

[JimLev]

Did you block off part of the radiator with cardboard ?
The t-stat heater functions when the engine is under high load or the DME thinks the engine should run a bit cooler.
The voltage going to the t-stat heater makes the t-stat open more so you can get more coolant to the radiator to cool the engine down.

......you beat me Chris.

[peter540]

Thanks, Jim and Chris! So the heater serves the opposite purpose than I imagined.

Jim, I haven't done the cardboard trick yet. That'll be next. Any advice for how to do that with my Zionsville radiator?