Need help with P0118 and P0125 codes on 2001 325ci

[dknight526]

Hi,
My wife's car just started seeing these codes. The only issue with the car I've seen right now is sometimes it is hard to start, that is, it cranks fine, plenty of battery and good starter, but just doesn't catch. I looked the codes up, and I don't see that they are related to the random hard starting. Where should I start? I'm up to doing most repairs myself, as I'm currently reworking the suspension on the car, but haven't dived into the motor much except for the basics. Any suggestions or other things I need to look for would be great!

[dworthy]

Well I would start with looking at the fuel pressure. See a bad fuel pump will not trip the SES light, so you will need to connect into the schrader valve on the fuel rail.

[bmwdirtracer]

P-codes are bureaucrat's mistranslations of the information you really need. These p-codes are often grossly incorrect, when used to diagnose BMWs. It's far better to use a BMW specific scan tool, rather than an OBD2 code reader.

That said, P0118 indicates that your engine coolant temp sensor is not delivering correct information to the DME (engine computer), and it is likely open-circuit (either failed, or unplugged, or having bad wiring.)
P0125 indicates that the coolant is not reaching sufficient temperature for closed-loop operation....or at least the engine computer doesn't think so (because the sensor circuit is open).

The engine coolant temp sensor on your engine lives in the cylinder head, at the very rear of the engine, underneath the intake manifold. You will not be able to see it, but if you remove the cabin air filter tray (4 T30 screws), you'll be able to feel it, and see if it's unplugged. A mirror-on-a-stick may allow you to see whether a rodent has caused wiring damage.

Officially, to change the sensor pays 3.5 hours, because it is assumed that you'll have to remove the intake manifold and many other items. I have a "cheat" for this, but it is not easy. You need to work in a tiny slot of space behind the manifold, and, using a 22mm open end wrench that is cut down to ~4 inches long, you can just manage to undo the sensor.. You'll need a new genuine BMW or OEM sensor, (no cheap Autozone Chinese stuff), and a crushwasher.

EDIT: Oh, and this would absolutely cause hard starting, because the engine computer will be injecting WAY too much fuel, if it thinks it's negative 40 degrees. Oh, and I just looked up the hours paid for this job: it's actually 4.0 !!

[dknight526]

Thanks to you both. I checked the coolant level, it was low, so I added more, and reset the codes. After driving around for a bit, the check engine light did not come back on, so I'll have my wife continue to monitor the hard starting. I think I recall reading somewhere that you can use a reader to see what the DME thinks the temp is. Do I need a BMW specific reader to get at that? Also, is there somewhere I can go to find a good independent in my area? I do most of my own work, but the sensor sounds like more work than I want to get into.

[bmwdirtracer]

The low coolant level would not have caused those codes.

And so you know, this job is one of my favorites, along with control arm bushings, because I can do the job in maybe 20 minutes....and get paid for four hours. It is NOT a lot of work, if you use the "cheat". And just think how good you'll feel about saving four hundred dollars!

[dknight526]

I did the lower control arm bushings last year, hardest part was pressing the bushing back onto the control arm. So, I drove the car around a bit, and did notice that the temp gauge spiked to high. Turning the car off, then back on registered a normal temp. I'll take a closer look at your cheat, what is the part "officially" called that I need to replace (I use Rock Auto for most of my parts)?

[bmwdirtracer]

Bad Boy. No Rock Auto. Try ECS Tuning or FCP Euro or Pelican Parts.

Part number : 13621433076

part 3 in this picture: http://www.realoem.com/bmw/enUS/show...diagId=11_2169

https://www.ecstuning.com/Search/Sit...h/13621433076/

I recommend genuine BMW, or Rein, or FAE

[WadiM3]

The reason your car temp spiked high I assume is because you didn't bleed the system correctly. The procedure is in the FAQ thread at the top of this sub forum

[bmwdirtracer]

The temp didn't spike.

It's difficult to start, and the codes indicate that's because the computer thinks it's very cold...


Here, look:
https://www.obd-codes.com/p0118

[MarcoZandrini]

OP, google “bmw E46 hidden obc functions.” Test #7 shows the coolant temperature as seen by the engine computer (DME). The sensor for this data is located in the cylinder head between cylinders 5 and 6. The gauge is controlled by the DME. That’s another wussification of the brand IMHO.

I’m betting the non-OEM thermostat is bad. Buy and install a Whaler thermostat. The cooling system is the E46’s Achilles heel. Installing aftermarket cooling system parts is verboten (forbidden) unless you want a very heavy and expensive paperweight, aka an overheated M54 engine.

[dknight526]

BMWDirtRacer, I now have the parts AND the short wrench (ECS will now be my go to site for parts, tx). Couple questions on the procedure. 1) do I need to worry about any coolant leakage when I remove the old sensor? 2) After replacing the sensor, do I need to worry about bleeding the system, and if so how is that done? Thanks for all the info, I'm off this week (Thanksgiving) and wanted to get this done before it gets too cold to do (I live in New England).

[bmwdirtracer]

Yes, there's a fair bit of coolant above that sensor, so you're going to need to bleed air from the system afterwards. Personally, I always use my vacuum-fill system, which puts an end to bleeding issues. However, you'll find a How-To for bleeding in the FAQ thread at the top of this forum.

You'll need a T30 socket (for the 4 screws which hold the cabin filter tray), and a mirror on a stick, plus a good flashlight, to see where you're going with that wrench. There's a crushwasher involved here, I'm pretty sure.