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Coolant Temp Sensor Testing Replacement
 
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Pelican Technical Article:

Coolant Temp Sensor Testing Replacement

Nick Czerula

Time:

2 hours2 hrs

Tab:

$50

Talent:

****

Tools:

10mm socket, flathead screwdriver

Applicable Models:

Volvo V70 (1998-01)
Volvo V70 2.4T (2001)
Volvo V70 AWD (1998-99)
Volvo V70 GLT (1998-00)
Volvo V70 GLT SE (2000)
Volvo V70 R (1998)
Volvo V70 R AWD (1999-00)
Volvo V70 T5 (1998-01)
Volvo V70 X/C (2001)
Volvo V70 X/C AWD (1998-00)
Volvo V70 X/C AWD SE (2000)

Parts Required:

Engine coolant sensor

Hot Tip:

Work with a cool engine

Performance Gain:

Remedy a check engine light or incorrect engine temp gauge

Complementary Modification:

Replace coolant at same time

The coolant temperature sensor on Volvo models with a normally aspirated 5-cylinder engine is mounted in the coolant housing on the right side of the engine, below the thermostat. It monitors the engine coolant on the engine side of the thermostat. This provides an accurate reading of both banks of the engine. The sensor is a negative temperature coefficient (NTC) sensor. This means as engine coolant temperature increases, sensor internal resistance decreases, causing a drop in sensor voltage. The engine coolant temperature sensor is responsible for sending the temperature of the engine to the DME and then shared with the instrument cluster via bus signal. This data is used in conjunction with other signals to determine the correct engine timing, fuel injector pulse along with other adaptable features. It is the main sensor used to operate the electronic cooling fan.

It is a two-wire sensor. One wire is the reference voltage monitored by the DME to determine coolant temperature. The other is a shared ground wire, shared with the engine oil sensor and the engine pressure sensor. If you have a coolant sensor fault code stored in your DME and your engine isn't running right, I suggest replacing the sensor before digging too deep. You may also have an inaccurate temperature gauge in your instrument cluster. This can also be from a faulty sensor.

Remember that your car may have been serviced before and had parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve, as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

In this article, I'll go over the steps involved with replacing and testing the engine coolant temp sensor on Volvo models with a normally aspirated 5-cylinder engine.
Figure 1

In this article, I'll go over the steps involved with replacing and testing the engine coolant temp sensor on Volvo models with a normally aspirated 5-cylinder engine. It is mounted in the coolant housing on the right side of the engine, below the thermostat. Place a drain pan under the right side of your engine. You can drain the coolant. However I find very little leaks out during the procedure.

Testing: Working at the coolant temperature sensor, press the release tab (green arrow) and pull the electrical connector straight out to remove it.
Figure 2

Testing: Working at the coolant temperature sensor, press the release tab (green arrow) and pull the electrical connector straight out to remove it.

Testing: Working at the DME side of the sensor connector, test the voltage from the DME with the key on and the engine off.
Figure 3

Testing: Working at the DME side of the sensor connector, test the voltage from the DME with the key on and the engine off. Terminal 1 (red arrow) should be about 5 volts (green arrow). Terminal 2 (yellow arrow) should be about 0.1 volts.

Testing: Working at the sensor side of the connector, test the sensor resistance.
Figure 4

Testing: Working at the sensor side of the connector, test the sensor resistance. The sensor when at room temp (about 60°f) should read 3.45k Ohms. As the temperature increases, resistance should decrease.

Replacing: Disconnect the electrical connector as mentioned earlier.
Figure 5

Replacing: Disconnect the electrical connector as mentioned earlier. Working at the radiator hose, use a flathead screwdriver to loosen the hose clamp (red arrow). Next, remove the coolant hoses from the thermostat housing. Detach the electrical connector from the bracket using a trim panel tool. Using a T35 Torx driver, remove the two thermostat housing fasteners (yellow arrows).

Replacing: Remove the thermostat housing (green arrow) from the engine.
Figure 6

Replacing: Remove the thermostat housing (green arrow) from the engine.

Replacing: Clean the area surrounding the coolant sensor.
Figure 7

Replacing: Clean the area surrounding the coolant sensor. I find this area can become quite corroded. You want to prevent dirt from entering the engine once the sensor is removed. I use a flathead screwdriver wrapped in a rag and soapy water spray. Using a 19mm wrench, loosen the sensor (green arrow).

Replacing: Unscrew the sensor (green arrow) from the engine.
Figure 8

Replacing: Unscrew the sensor (green arrow) from the engine. Install the new sensor with a new sealing gasket (red arrow). Reinstall the thermostat housing with a new sealing O-ring. Top up and bleed the cooling system.





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