cn90 » Most Engine Coolant Sensor works by NTC principle: as temp increases, the resistance (measure in Ohm) decreased…
For example, I measured the brand-new Volvo ECT and got these values
- -20C: 16,000 Ohms (16 kOhms)
- 0C: 7,300 Ohms
- 20C: 2,600 Ohms
- 80C: 300 Ohms
- 90C (Operating Temp): 200 Ohms
- 100C: 150 Ohms
So, when it is cold, the ECU injects extra fuel to start the engine. The problem is, when the ECT fails, it usually fails in “HOT” position (short-circuit inside the sensor), I have these 2 symptoms:
- Aux fan runs on its own for about 6 minutes or so.
- Hard start when COLD (ECU thinks it is hot and no need to inject extra fuel when it is COLD).
So, if you got stuck in the middle of nowhere with this problem and need to go home, you can use a resistor that simulates COLD engine (such as 20C with 2,600 Ohm or about 2 KOhms), to start the engine. Once warmed up, you can re-connect to the defective sensor to drive home.
Parts
* Volvo PN 9186486, Made by SWF (Germany).
* Ebay has same SWF for $39.
Tools
* Coolant
* T40 Key and 19-mm Wrench
* Some random resistors in case you want to play with the ECU.
Procedure
* If you have not replaced the tstat, then consider replacing it. I replace my tstat every 70K.
https://www.matthewsvolvosite.com/forums … =1&t=50745
* With long T-40 Torx key, remove the bolts and push the tstat housing aside to expose the ECT.
* Use a screwdriver to push the connector outward. The connector is very difficult to pry apart. I broke the plastic tab, so I used Zip Tie, no big deal.
* I use a pair of cutting pliers to cut the old ECT plastic sheathing to remove it (it was bonded to the harness very tight!). Look at the new ECT so you know where to cut on the old ECT.
* Note that I already disconnected the Aux Fan (because it was running!).
* Use 19-mm wrench to remove the old ECT sensor. When installing new ECT sensor, don’t forget to remove the old Aluminum washer! Also don’t forget to use the new Aluminum washer.
* Due to tight space, turn the 19-mm wrench sideway to tighten the ECT. Just snug it then tighten it. Don’t over-torque it.
* Now re-install the tstat housing.
* Refill reservoir with coolant to Max, start engine, drive around blocks and check coolant level later. You will need to add a bit more coolant later.
* That’s all folks!
DIY: 1998 V70 ECT (Engine Coolant Temp) Sensor Replacement
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4 Comments
[…] ECT Sensor: on a similar note to the O2 sensor, these also have a finite life at about the same mileage and OEM Volvo sensor is best as this sensor is also responsible for how well your car will run and start (cold and hot) and the fuel consumption so the extra money is well spent. While you are replacing the ECT, replace the thermostat with Volvo OE as they fail safe. Typical symptom is a car that runs cold. Aftermarket thermostats tend to fail closed which is bad. […]
Changed ECT sensor but fan still runs when car is started and ck engine lite still on my car is a 2001 c70 convertible any idea what I should check next
C70 coolant fan won’t come on causing tank to burp coolant , changed the relay but not the fix? What’s next to try?
Had a similar struggle to cold start problem with a check engine light and an erratic temp gauge. The Dealer offered to look into it for the exchange of 100 Federal Reserve Notes. Thanks to this website, I saved said notes, not to mention labor and other unesessary wallet shrinking rabbit holes. Thanks.
FV