Coolant Temperture Sensor and Oil Pressure Mix Up?

[flywheeljack]

So I have been working this little problem since I bought my VERY beat up 318i . The CEL is on and the Oil light slowly makes it way to bright while driving and the temperature gauge gets to (but not quite in) the red zone.

When looking around the engine compartment i found a lot of oil had been leaking for a long time from the oil filter housing, so i changed the gaskets and o ring which stopped the leak.

The oil light still comes on slowly, and the temperature gauge still works its way to the red but still not quite.

So I decided to diagnose the CEL. It came out as 1223 which is the Coolant Temperature Sensor. Replaced with a new sensor, and reset the computer. The same code comes up and everything is the same.

So just because I know this car has been worked on before, I decided to switch the connectors of the Coolant Temperature Sensor and the Oil Pressure Sensor around.

Reset everything, started her up, and the CEL no longer comes on. The Oil Light is not coming on but the Engine Temperature Gauge goes to Hot immediately on startup....no light comes on though.

I suspect that maybe because this car has been worked on in the past that maybe the connectors were switched around...or maybe not...how can I be sure I have the correct sensors connected?

Any ideas?

[Jack Dabsy]

Hmmm... Which coolant temp sensor? On the head, or the rad?

[flywheeljack]

Hmm...din't realise there were 2 Coolant Temperature Sensors. I only found 1 in the Bentley Manual. I replaced the one on the head. Would the 1223 code come up for another sensor?

[brettski]

Welcome to the Werkz.

The fact that the temperature guage is going straight into the red on startup (even when cold?) would suggest to me that you have the temperature guage connected to the oil pressure sensor. Disconnect that wire (currently on oil pressure sensor) and see what happens on the temperature gauge, if it doesn't budge until you reconnect it, then move the wires back to the other positions.
Let us know what happens

[Jack Dabsy]

As Brett says... Also make sure the wires are not grounding elsewhere !

[flywheeljack]

Ok so I switched the sensor connections back to their original positions, and I get the original warning lights. The CEL comes on - check the code and its 1223, The Oil Pressure light comes back up slowly and the engine temperature makes its way to hot (but not into the red zone)

Now don't get me wrong, I switched the connectors to see if perhaps the guy before me had mixed something up - doesn't look like it though. But the 1223 error is making me crazy. I tried testing the wire from end to end for continuity on the connector... but didnt get anywhere, (to do this I unclipped the DME computer and tried testing the sensor leads from that end to the connector- got nothing, perhaps I did it wrong)

The Oil Pressure though I know whats going on, theres a leak in one of the gaskets around the cylinders. I changed my spark plugs recently and found oil on all of them from inside the cylinder... so I'm looking at either blown valve cover gasket, head gasket or bad piston rings...blahhh.

Anywho...I have no doubts about why the temperature gauge is climbing to hot being connected to the oil leakage, but I do want to stomp on the sensor bug before I put down the coin to change the gaskets (heres hoping its only the ones on top and not the rings ...)

Any suggestions as to how to check the wiring for the Coolant Temperature Sensor connection would be appreciated and any advice on the oil leaking into the cylinders is also invaluable...

[rivroshaun951]

Few....looks like you have a few things going on here. First I would like to say. I am not a professional. This is just my opinion. I could be wrong. Okay let's start with a warning. Something I might have misread but it looks like you said you tested the computer circuit wire for continuity. I would strongly advise you never test for continuity when dealing with any circuit that is connected to any type of PCM, ECM, ICM, etc. Computers are highly sensitive to electrical load and you could possibly damage the computer. Now testing the actual sensor for how much resistance (not just continuity) and comparing it to Manufacture specs is what you want to do. Now remember this sensor is a Temperature sensor. It is a "Thermistor". As temperature changes it will have greater or less resistance. The computer sends 5 volts (BMW might be different). to the sensor. The sensor at a certain temp has a certain resistance and so there is a voltage drop at the sensor (load). The computer reads the voltage drop and that is how it knows what temperature the coolant is at. The computer dose not know exactly what the temp is. It just reads the voltage drop at the sensor and responds to whatever it is. Now that you know how the sensor works you need to find out which type you have. There is a negative coefficient thermistor (most widely used) and a positive coefficient sensor. Knowing which type you have will let you know what type resistance you are suppose to get at what temperature. Now to properly test this sensor....your going to have to look at your repair manuel and find the specs and procedures (some procedres call for taking the sensor out, putting it in boiling water using a thermometer and test for resistance).

Now back to your computer. Use a DMM (digital multi meter) and test for available voltage (not continuity or resistance). Again you will have to refer back to your repair manual to get the specs. But my guess is on the power side you should get somewhere around 4.5v to 5 volts.

As far as your Oil pressure and pulling out your spark plugs. Look at the condition of your plugs. That will give you a hint on if your problem is internal leak or external. Are the plugs fouled? Are the clean? (you woudl be looking at the electrode). Also if you had bad rings you might have smoke from burning oil coming out of your tailpipe. Do a quick vacuum test to see if you have a vacuum leak. If you do then follow in up with a compression test, then leak down test. The leak down test is the fo sho way to find out if you have bad rings. A blown head gasket to me sounds like you would be burning coolant. Again notice any smoke coming out of your tailpipe. Check your coolant level. OH SNAP!! maybe thats why you have both issues going on. See how this works. if you would like. I might be able to find you a trouble tree for your 1223 error code. It just depends on how tight ass BMW are with there codes.

My final thought is if you replaced a sensor with a known good one. Maybe it's not the sensor. maybe it's (I really hate to say this)....Maybe it's the PCM. But remember before you doom the pcm. check the sensor compare it to specs. Check the circuit compare it to specs (Don't forget to check power and ground). Or maybe you are really running HOT and you need to check your coolant level and do a pressure check on your cooling system. I know I said check the cooling system last. I did that for a reason. If you did not check it already. The last statement should have rung the bell. Again. Check the coolant level....then check pressure of your cooling system.....then check your oil to see if your loosing oil....basics first.

[Jack Dabsy]

Well, I cannot beat that explanation today.. Maybe just add that oil can seep into the bores via worn valve-guides (noticeable with lightish-blue puff of smoke at cold start-up)...