disus

Hey MB peeps,

I have 2004 MB C230 Coupe.

I am losing my mind with this issue. A couple years ago, "Check Engine" light came on and I have been trying different advices to get to the bottom of it, but it keep coming back. First time it came up, it showed error P0128, I went to the shop and they said it was related to sensors, replaced both water temp sensor and thermostat. The light came back on that day. They gave up.

Another shop told me it was related to O2 sensors somehow, so I had those replaced. It came back on about a week later, P0128.

I have a friend with the same diagnostics equipment as MB dealership, who checked operating temp to see if there is an issue and it operates normally. Also checked other operations of the car that could be involved in the issue, everything is normal. Coolant level is fine. AND even the gas cap is on tight.

It's not that the car drives any differently, but the light comes up.

For MB Dr. House : I noticed that the times it does come up is when I get on the freeway after the car sits for 8+ hours, about 5-10 minutes into the drive, boom, P0128. However, on regular city roads, it very rarely comes on (may be once in a few weeks). The temp gauge shows normal temp [ may be just a tad less than half ]. If I drive in city first, then jump on the freeway, no problem. It's only cold > freeway is when it comes up after about 5-10 mins of driving.

If I had to put my mediocre knowledge & guessing, there is a "timeout" that computer has that determines [ temp of coolant ] / [ time of the drive ]. If the value is below that "timeout," it throws an error. Since I assume that it takes more time for engine to reach a certain temp on the freeway due to cooling factor at higher speed, that timeout is off or the coolant needs to heat up faster [ aka add water? ].

Browsing around, people have mentioned it could be "coolant temp sensor" or "coolant fan" (running too much).

Any thoughts before I start putting on my bridge-jumping shoes?

SeaCoupe

Perhaps a partially stuck open Thermostat?

http://www.obd-codes.com/p0128

What does that mean?This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125

In determining the engine did not reach a "normal" temperature, it takes 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.

Symptoms
You will likely not notice any drivability problems other than the MIL illumination.

Causes
A code P0128 may mean that one or more of the following has happened:

Low engine coolant level
Leaking or stuck open thermostat
Faulty cooling fan (running too much)
Faulty coolant temperature (ECT) sensor
Faulty intake air temperature (IAT) sensor
Possible SolutionsPast experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on

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.
If the above items check out good, replace the thermostat

disus

Thanks emrliquidlife for being the first to take a stab. That was the first thought of everybody. But as I mentioned, the first shop replaced thermostat, and it came back on that day. Unless the second one got stuck open as well... is possible. Thermostat can still be the culprit, I agree.

SeaCoupe

New sensors, a new thermostat....I assume you have the coolant level up to spec. Then that only leaves the Intake air temp sensor. This is located in the body of the MAF. Try running the car without the MAF plugged in. See if the code doesn't come back. On my M111 engine, I can run without the MAF plugged in.

Or, if you have an OBD 2 reader with live data, you can view the IAT. I think, and I'm saying I think, they run some 30-50 degrees higher than ambient temp. So if the IAT reads 100, the car has been on for 10 minutes or more, the IAT is toast.

disus

Thanks again emrliquidlife, the IAT is worth exploring. Any other thoughts?

SeaCoupe

The IAT or the fan switch being constantly on are all I have.

If you are in SoCal, I have the OBD 2 reader.

TruTaing

disus - I had this same code come up for me several times when I was replacing my thermostat. I was given the "cooler" thermostat and my p0128 always came back no matter what I did. I went to a stock thermostat and my p0128 has never returned. I have not heard of previous owners having problems w/ any thermostats, but I just figured the 'new' thermostat I got was malfunctioning at the very start, and thus causing problems. I wouldnt be too surprised if the 'new' thermostat you got was malfunctioning also :x

disus

Unfortunately, all the way in Northern Washington. A friend of mine has the tools needed to diagnose this. I am just crossing fingers it's something minor, not an issue related to the computer itself...

I have also read somewhere it might be a grounding issue. You don't think so?

disus

TruTaing - I would love if that's the case ha, would hate the fact that replacing O2 sensors wasn't necessary, those *******s weren't cheap. Could have paid for at least 20 lap dances ha

TruTaing

hehe, its a good lesson Its always easy to go replacing things, but it never hurts to question your "fix" and why it is the most likely cause of your headahces (why you replaced it first) and why it didnt work. Trust me, ive learned this lesson far too many times.

Where are you in Washington?

disus

Yes, this wouldn't be the first time of learning something the hard way... I wonder if I get discount if I pre-purchase 20 lap dances ha

I am in Bellevue.

TruTaing

Ah, I roll through bellevue all the time - definitely cross 520 far too often. Hit me up if you're trying to mod

disus

520 is almost always a cluster - gotta love that traffic. I think I am done with modifying the Benz or putting money into it (had to replace alternator, window regulator, tie rod + alignment, turn signal switch, and upcoming thermostat in the last 4 months). I don't have much on it in terms of mods, just H&R springs, Rims, and PIAA lights. Looking to sell it soon [ leaving the Benz world for Infiniti G35 ]. Before selling it, wanting to fix some issues - hence the thread. Here is mine:

TruTaing

Ah, okay. Havnet seen ya around at all :P GL w/ your sale.

ellasman

DISUS... ok, check this out. A similar scenario happened to me about a year ago. Here in Florida - all of our gasoline is 10% ethanol... from what I know, ethanol mixed with the gas makes the engine exhaust no burn as hot as its supposed to. Its a long story on how I know this, i traded in my passat for this same reason for a benz as you're about to read below...

I bought my 07 c230 in Feb of 2009 - year end closeout.... drove the car for two months - randomly the check engine light would come on/off on/off at all random times - the MB dealer couldn't figure it out... it kept saying exhaust fail... they would reset the computer, run diagnostic, everything would check out.... end of that month.... MB USA released a firmware update to the engine's computer to change temperature tollerances on the heat output of the engine.

Moral of my post - go to your MB Dealer - ask them if there's a Firmware updated for your car to compensate for the sh***y ethanol that's mixed into our gasoline.

It may cost you an hour of labor, but it may fix your problem!!! No offense to the corn agro people... but corn is for agro feed and for food... not for gasoline... that's why we drill for crude !!!! we grow corn for food... we drill for crude oil... simple concept, but the us gov seems to think better!!!

hope this helps

disus

ellasman - that's an interesting point. Because the issue is so sporadic, that's what I was starting to think as well - whether it's related to the computer itself than a mechanical part. Definitely worth a shot.

fanito

You have the same issue that I had b4... sad, very sad...
(Thead: https://mbworld.org/forums/c-class-w...y-arrived.html)
So you know, it got misdiagnosted the 1st time. Actually not that much, the problem was a bad o2 sensor and a bad thermostat. $950 + star diags (believe me, a must!)

disus

Hey fanito - I found the notice for recall for that part. And just scheduled my car in for next week. I wonder if my air sensors are still ok since I had them replaced about 6 months ago. I will run that by MB. I was reading the recall, and it said that you may get reimbursement if you had the procedure done elsewhere. Were you able to get that?

I am hoping this will solve the situation, this CEL has been driving me nuts.

fanito

well, they did the campaign for free and replaced everything (soleinod and added ties) for free... there are 2 o2 sensors in your car, do you know which one is it? more than likely you won't have to replace it and the OBD2 just gave you an indication of a faulty part but not necessarily that could be the main culprit (meaning that is failing because other component is failing as well...). I recommend you to get it diagnosed with star, while using an OBD2 will give you good information it will not have the same capabilities than Star Diagnostics.

disus

I had both O2 sensors replaced, but it didn't fix the CEL problem. Was your OBD2 showing P0128 by any chance? A friend of mine has the same equipment [ DAS / SDS ]. We ran it through and it said that there is an issue with coolant temp, but we monitored and it was operating and optimal temps. That's why I am also partial to TruTaing's suggestion that it might have been a faulty thermostat that got replaced.

disus

Hey guys, thanks to everybody who contributed to this discussion.

I had the solenoid replaced as per recall. Of course they called me about the CEL. They said they are pretty sure it is the thermostat and gave me a quote to replace it for $360 or so. Why pay more than needed? ha

Ordered the part from PartsGeek for around $25, and it arrived the next day. My buddy [ who is a mechanic ] and I installed it in under an hour. The CEL seems to be gone.

So, every now and then you get a faulty part from Mercedes and lose a lot of hair and sleep trying to figure out an issue that is much simpler than originally anticipated. I guess this really turned into one of those "House MD" episodes where the answer was right in front of the nose.

korym

Hi I'm a newbie here. I have a 2002 C230 Kompressor with the PO 128 code. I have already replaced the thermostat, cleaned the temp sensor leads, checked to make sure that the AC is off. I noticed that the fan is running on low all the time (37 deg mornings) when engine is running. The temp gauge seems to be working in that it registers the temperature. I would guess that if the fan runs all the time the engine will never reach the normal operating temp and throw the code. What should I check next? any help is apreaciated!