Looking for some troubleshooting help.

I had my check engine light come on with the code P0118- relates to the coolant level or sensor. The fan would stay running for a couple minutes when the car was turned off, and when trying to start it would have trouble but then eventually starts up.

I replaced the coolant temp sensor (IAT) and the CEL went out and car shut off without the fan running and started right up. Drove about 20 miles and the CEL is now back on and fan continued to run again after turning the car off.

Should I replace something else? What should I try next?

Any help/input would be greatly appreciated. Thanks.

 

Check and clean the connector with electrical contact cleaner. What brand of part did you replace the sensor with? I bought one from Advance Auto Parts a couple of years ago that never did work right.

...Lee

 

Bought the new sensor right from the Volvo dealer. I will try cleaning the connector and see what happens.

Thanks.

 

Is the same code set or are you just assuming it is?

 

Yes, same code same symptoms. I'm puzzled. New sensor from the factory, good connections. Hoping its not a faulty sensor and I'll need to try another one. Is there a way to test to sensor to see if it is operating properly?

 

Just for clarification, the IAT is the Intake Air Temperature Sensor and the ECT is the Engine Coolant Temperature Sensor. P0118 is indeed an ECT error code.

You can drop it in a pan of water and heat it up.

The resistance / Temp (degrees C not F) readings are as follows:

0 degrees - 5740 Ohms
10 degrees - 3700 Ohms
20 degrees - 2450 Ohms
40 degrees - 1150 Ohms
80 degrees - 318 Ohms
100 degrees- 184 Ohms

...Lee

 

I have the same problem with my 98 S70 (non turbo). I replaced the thermostat and coolant temp sensor about 2 years ago. Car will never really get up to temp on cold days. Fan runs for a while after shut off meanwhile the temp gauge is buried.

 

Took the readings, the sensor seems to be giving the proper readings.

The ECU end is reading 5.4 K Ohms at a fairly warm temperature. I read somewhere the reading hot should be 5.59 K Ohms and cold 5.56 K Ohms. Is this reading close enough the the required range? Or could this be the problem?

Thanks.

 

When our S70 overheated it messed up the temp sensor. So I installed a new one and it went bad in about a week. So I got an old one from a junk yard and it has worked great.

 

So the readings from your sensor correlated to what Lee posted? How did you test it?

?? All your readings are above 5000 ohms which per Lee's table is in the neighborhood of 0 degrees C or 32 degrees F which I would not consider "warm". You're not reading this with the ECU in the loop are you?

Here's the table from 850 manual which pretty much jibes with Lee's:

ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE TABLE
Temperature F (C) Ohms
32 (0) .............................................. 7300
68 (20) ............................................. 2800
176 (80) ............................................. 300
212 (100) ............................................ 150

So if you are truly reading over 5K ohms once engine is warmed up and you've validated your sensor works then I'd suspect your thermostat is stuck open? Have you ckd that? Where's your temp gauge at?

 

I checked the sensor using a mulitmeter, which those readings were accurate to what Lee posted.

My temperature gauge goes up to around the 4 oclock position and doesnt move.

A quick update: I clean the new sensor connector and put some lubricant on it. Car has been starting fine and shutting off without the fan running. Check engine light is still on.

I will check out the thermostat.

Thanks for all the help.

 

Sounds like you need a new thermostat; gauge should be at 3 oclock (or just a hair above) and it appears like you can trust it since you tested the sensor...

 

Here is the true:
I've just replaced my ECT sensor with spare one and tested it on the road. The gauge is where it should be (at 3 o'clock). I'm happy and the car also!

The mechanical part:
I took out my old ECT sensor and submerged it along with spare one in the same pot filled with antifreeze, for same measurement conditions. My old sensor showed ~6.5kOhm, spare sensor ~ 2,8kOhm. The higher Ohms mean lower temperature (see table in the beginning of this topic). That's why I've got those symptoms: cooling fan doesn't turn on, temp gauge needle at 4 o'clock and overheating in traffic jam.

I red many posts about how ECT sensors fail, but they usually get a shot circuit, that cause cooling fan always on. The same thing is when your ECT sensor is totally unplugged. But in my case incorrect ECT sensor readings were the main problem.