ECT sensor/ thermostat.
 

96 volvo 850 GLT: Car was running hot in traffic but normal on hwy. Got home and ran the codes and came up with PO118. So I'm replacing the ECT sensor and the thermostat. By the way the rad. fan is not working. I'm hoping it's the sensor. I cant find the original 87C thermostat except for a co. called Vaico. Volvo only makes the 92C. Anyone have any advice about the thermostat brand and temp? And the ECT sensor can run from $65.00 for volvo down to $23.00 for a co. called Facet. Thanks.

OK - car was running hot in traffic - I guess you noticed the temp indication on the gauge was higher than normal - that means THE SENSOR IS WORKING, probably the thermostat also.

You also noticed the fan was not working,

Why don't you check the fan since the gauge is working and maybe the thermostat also. By the way if your car is running hot - and you don't want it to - turn the heater on full blast, that can help cool the engine if the fan is not working and try turning the ac on to see if the fan will come on due to ac pressures - if not you may have a bad fan or fan relay. The thermostats usually fail by breaking and sticking partially closed. That results in the engine taking longer to warm up and sometimes/most of the time will set a thermostat code - because the engine is too cold for too long.

On the diagram the relay is 2/11 mounted on the fan shroud, and the fan motor is 6/29. Check for 12 v at the big red wire on the relay. And try to apply power to the red and the green wires (for the two speeds) going to the fan to test it. I have seen bad fan motors or with only one fan speed working, and plenty of bad relays or melted connections. Never a bad fusible link but it's possible.
https://cimg2.ibsrv.net/gimg/volvofo...c86bfdfcab.jpg

Thanks for the quick reply hoonk, I tried to ck the ECT sensor for corrosion and when I disconnected it ,or tried the two pins pulled out of the sensor and are stuck in the connector end. Wires are still intact so ill see if I can plug it back in. Ill ck codes again to see if that has thrown another code. If not I'll check the fan connections. Although I will say I'm no tech but maybe after comparing the schematic while looking at the fan I might be able to find the connection that might be bad.

ECT sensors can be tested with a VOM. You can google for a resistance chart but to test, disconnect the ECT connector and measure the resistance. for a cold engine, the impedance should be in the 3K-4K range (varies by ambient temp). For a warm engine, the resistance will drop all the way down to 200 ohms at 95C or so. Changing out the ECT and T-stat as well as the overflow cap should be considered normal maintenance, but +1 with hoonk in that they are not likely to be the cause of running hot in traffic. More practical is 1) fix your fan 2) do a coolant system fresh water flush/refill with fresh "green" 50/50 coolant. 3) refresh the ECT/t-stat/cap (original specs - don't over think the temp setting of the t-stat. Once its opened its open. These cars run a closed pressurized cooling system so its normal to see temps in the 102C /215F range when in traffic.

I have never replaced the t-stat or the ECT sensor. I have flushed and replaced rad. fluid. Now that I've tried to remove the ECT and like I said before the pins are stuck in the connecter side I'll have to replace that along with a new t-stat. I swear the info on PO118 pointed directly to the ECT sensor, but like hoonk said the temp gauge is working so its not the t-stat.. I thought the ECT wasn't sending signal to the fan. Wanted to start with the least expensive. Around $350.. for the new fan and Iv'e read they don't fail often. I'm at 120k oig. miles.

Yes that code is related to the signals from the ECT sensor - If your thermostat is stuck open, you will get a ECT code - the control units expects X temperature, if it reports X-20 temp - control unit sets a code. Thermostat stuck closed, same response - code is set, ECT is working fine.

The codes don't mean a part is bad - in this case the code means the signals are not within normal operating parameters. Codes just point you in the right direction. Here's what Volvo says about a typical ect code. (there are 6 variations of ECT codes that Volvo has explanations for, this is one of the 6) And the temp gauge working means the sending unit is (was) working, not necessarily the thermostat - you may have gotten a ect code because the car is overheating due to your fan not working. The ECT reported a temp not in the normal range in that case. Note Volvo does not suggest - "no coolant in engine, or "fan not working - it's overheating" - they expect you to check the basics.

https://cimg1.ibsrv.net/gimg/volvofo...2d011b17d4.jpg