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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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Old 05-20-2010, 09:28 PM
bbakerga bbakerga is offline
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Location: Atlanta
Join Date: May 2010
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Mein Auto: '03 330ci convt
Help please... coolant temp gauge erratic/crazy!

OK, so I'm kinda stumped... here goes. (sorry in advance it's so long, I wanted to make sure I gave all the info I have)

2003 330ci convt. car runs and drives fine.

My SES light came on... and a later that day the car went into limp mode. when I scanned the codes, it gave me the following:

p0118 Coolant temp ckt high input
p0734 Gear 4 ratio incorrect

I didn't get too worried about the gear ratio/tranny code, because it always seems that it throws codes like that when there is another issue... when I fix the other issue, the transmission codes stop, too. but, FWIW, those were the codes.

I cleared them, and drove the car... it ended up throwing the coolant temp/high input code again (P0118), so I replaced the coolant temp sensor down on the lower radiator hose. Same thing.. only this time, I noticed that the temp gauge will occasionally FREAK OUT. it is usually right in the middle (as is typical) but then.... it will all of a sudden go WAY up... buried on the red/hot side... it might stay there for 15 or 30 seconds... sometimes, it comes back down to normal, other times it will fall all the way to the cold/blue end. usually, after 30 seconds or so.. it goes back to normal. The car doesn't seem to be actually running hot, just the temp gauge says it is.

SO... I replaced the thermostat/housing. same problem... cranked up the heater to 91 and bled the coolant..... 3 times... same problem.

Tonight, after I bled, (and bled) the coolant, I decided to hook up my scan tool and watch the engine temp readings when the gauge went nuts.

When it finally did, the scan tool showed negative temps -12, -25... etc. while it was in the red/hot range.... as the needle swung all the way down to ice cold, the scan tool showed temps of slightly above 0.. and then up in the 20's... during this time the car ran rough... hesitated, and I shut it off.... tried to restart it, and it just turned over and over. waited a minute tried again.... started up, runs fine again.

I'm not yet worried about it running weird, because I'm sure that the computer is adjusting fuel mixtures, etc. when it suddenly thinks it's below freezing. However, I can't for the life of me figure out WTH is causing the car to think the coolant temp is going so crazy.

I want to avoid the process of just replacing components one after another until it's fixed... can't really afford that right now.

please help if you can, thanks in advance.

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Old 05-21-2010, 04:56 AM
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MicahO MicahO is offline
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Location: Warwick, NY
Join Date: Apr 2004
Posts: 1,397
Mein Auto: 330i ZHP
With behavior that strange (and since you already replaced the CTS), I'd look for a pinch or a short in the wiring harness for the CTS. The wiring on these cars is pretty well embedded in the harness, so it's not easy digging around. The most likely area for a break in a wire will be right at the connector itself. While the car is running, see if you can create the problem by twisting around on the wire harness (just watch out for the fan.....). This may pinpoint your break.

http://www.obd-codes.com/p0118 has a not-unreasonable set of troubleshooting tips for this code on just about any car. Don't discount the possibility of a bad new CTS, right out of the box.

--Micah O'C
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Last edited by MicahO; 05-21-2010 at 05:00 AM.
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Old 05-21-2010, 06:09 AM
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Solidjake Solidjake is online now
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Location: NYC
Join Date: May 2007
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Mein Auto: 02 330i 6MT
^ Try what Micah said and good luck.
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Old 05-22-2010, 05:09 AM
mujjuman mujjuman is offline
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Location: NY
Join Date: Feb 2009
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Mein Auto: hoopty
damn this is crazy. i was going to say classic case of t-stat malfunction but you already replaced it...
wouldnt this also be caused by air pockets in the system? i know you already bled the coolant.... but still. how likely is it that its a wire harness issue if it hasnt been touched
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Old 05-22-2010, 05:12 AM
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MMME30W MMME30W is offline
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Mein Auto: Ram 2500 4x4
Originally Posted by MicahO View Post
Don't discount the possibility of a bad new CTS, right out of the box.
Odd, but I would not be surprised if this was the case...
“Character is doing the right thing when nobody’s looking. There are too many people who think that the only thing that’s right is to get by, and the only thing that’s wrong is to get caught.”

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Old 05-22-2010, 04:31 PM
im im is offline
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Location: florida
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Mein Auto: bmw325i /318ic
would seem you have air in system:
did you fill the coolant properly?
little screw out
cap off
engine off but dash lights on with heater full on
filled fluid very very slow..repeated multiple times to very top of cap level/almost overflow..drinks fluid thru pencil hole near upper lip.
stop pouring fluid once over flow of screw hole,,replace screw
suck excess fluid from expansion tank
start car and look for it to pee out of little pencil hole
replace cap.
recheck when cold.
*Also check the electrical connection of sensor on top of radiator passenger side on fan shroud and sensor at bottom hose passenger side near radiator..If these are disconnected or car started with them disconnected it gives some weird codes regarding trans. and temps.
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Old 05-22-2010, 08:56 PM
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smolck smolck is offline
Location: Birmingham, AL
Join Date: Jul 2007
Posts: 22,513
Mein Auto: 2004 ZHP Sedan
Check your BATTERY! I bet it is low on voltage and needs to be replaced. It's free and easy

Check out my YouTube Channel for DIY's and other fun stuff HERE
Originally Posted by Fast Bob View Post
now, go burn your Man Card, and buy yourself a Camry....
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Old 10-25-2010, 01:23 PM
achauhan achauhan is offline
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Location: Leicester
Join Date: Oct 2010
Posts: 1
Mein Auto: 330Ci Conv
I have exactly the same issue where the temp gauge is erratic but the car drives fine.

Did you manage to find a solution?
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Old 12-06-2011, 03:06 AM
indyg2007 indyg2007 is offline
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Location: wolverhampton
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Posts: 2
Mein Auto: bmw 320ci 2000
Hi I'm having a similar problem but mine happened when I change the thermo and CCV valve. Any joy in getting it sorted.
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Old 10-03-2012, 05:24 PM
bkane bkane is offline
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Location: Atlanta
Join Date: Oct 2006
Posts: 1
Mein Auto: 200 528I
Did anyone ever figure this out? I have a P0118 code and the temp gauge is erratic. Sometimes it moves rapidly (in 2 seconds) from midway to full hot and then after about 30 seconds will drift back to midway. Also it will sometimes go from midway to the blue area and then return. Doesn't appear to be overheating and I have bled the system several times. Last fact not using any coolant. Is the only way to replace the coolant sensor on the head to remove the intake?

Last edited by bkane; 10-05-2012 at 04:18 AM.
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Old 02-26-2013, 10:07 AM
rockybmw rockybmw is offline
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Location: carpentersville,illinois
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Posts: 4
Mein Auto: 2003 330cic
Did anyone ever figure out this problem? Having the same problem with my 2003 330Cic
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Old 02-27-2013, 07:45 PM
Jimmys 530i Jimmys 530i is offline
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Location: Conyers, GA
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Mein Auto: 2003 530i
Check the engine temperature sensor. I just had to replace it on mine last night. It is under the intake manifold cylinder number 6.
2004 BMW 330ci Silvergray Sport Package, Cold Package, Xenon Headlamps, Premium Package, 6 Speed Manual, Build Date 9/03

Sold - 2003 325i Sedan Japanrot 5 Speed 8k Xenon Headlamps Build Date 11/02
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Old 03-02-2013, 02:51 PM
rockybmw rockybmw is offline
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Location: carpentersville,illinois
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Mein Auto: 2003 330cic
I'm having trouble locating it. Do you have pics?
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Old 03-05-2013, 11:47 AM
chet31 chet31 is offline
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Location: Madison WI
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Mein Auto: 05 330i convertible
Originally Posted by smolck View Post
Check your BATTERY! I bet it is low on voltage and needs to be replaced. It's free and easy
Everyone having electrical issues with an 8+ yr old car with the original battery. Please read this.
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Old 03-05-2013, 09:41 PM
heztheone heztheone is offline
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Originally Posted by chet31 View Post
Everyone having electrical issues with an 8+ yr old car with the original battery should be shot

Give a man a fish and you feed him for a day. Give a man a Chef and he feeds him for a lifetime
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Old 03-05-2013, 09:42 PM
vandyboy vandyboy is offline
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Posts: 297
Mein Auto: 01 325i automatikgetriebe
For God's sake, don't go bleed the system anymore or buy any parts until you test the freaking battery. Two people before me have told you want is wrong with the car. A bad battery makes the cluster (including temp gauge) go haywire. Go to Autozone or Advance and have them test it.
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