Coolant Temperature Sensor

Coolant Temperature Sensor monitors the temperature of the water in the engine. The PCM uses this temperature reading to adjust the fuel injection and timing. In some cases the PCM uses the reading from the sensor to turn on the electric cooling fan if so equipped.

Coolant Temperature Sensor  test for the Jeep Wrangler YJ

Where is the CTS sensor located?

On Jeeps there are two coolant sensors. There is one at the front of the engine in the thermostat housing, this one has two wires. Then there is another at the back drivers topside of the engine cylinder head just to the right of the valve cover, this one has one wire. The one wire sensor in the back sends temp readings to the gauge in the Jeeps dash. If you temp gauge isn't acting right, replace the one wire. The two wire sensor located in the thermostat housing sends its signal to the PCM. For poor performance issues and testing we are going to look at the two wire up front.

Will it trigger the check engine light if the sensor is faulty?

It can cause the DTC light to come on. Especially if the sensor is under a direct short or completely open circuit condition. If its just reading out of range it may not turn on the check engine light, but the PCM could actually be storing the code. If there is a code it will be code 22 per the light flashes. Click here to see how to get the DTC code from the Jeeps computer.

Why does it fail?

Wear and tear from age. Old coolant that has become corrosive. Leaking around where it screws in or where the electrical connections. Cracks in the plastic where the harness connects on to it. It's really not a sensor that fails often. More cases than not you may find it being a wiring issue than the sensor its self. But test that rascal anyway!

How do you test it to see if it is bad?

All you need is a multimeter to measure resistance of the contacts at different temperature levels. Also a way to vary the temperature of the sensor. Something like a pan of water on the stove top over low heat. Use a thermometer to measure the water temp as it climbs. Not the water temp as you measure the resistance and compare it to the chart below.

See YouTube video at the bottom of the page.

Below is the Temp to resistance chart for the Jeep YJ & XJ. It may work for other fuel injected Jeeps as well.

If you would like a printable copy Click here.

Temperature

Resistance (Ohms)

C

F

Min

Max

-40

-40

291,490

381,710

-20

-4

85,850

108,390

-10

14

49,250

61,430

0

32

29,330

35,990

10

50

17,990

21,810

20

68

11,370

13,610

25

77

9,120

10,880

30

86

7,370

8,750

40

104

4,900

5,750

50

122

3,330

3,880

60

140

2,310

2,670

70

158

1,630

1,870

80

176

1,170

1,340

90

194

860

970

100

212

640

720

110

230

480

540

120

248

370

410

Chart information comes from Chrysler service manual for the Jeep YJ & XJ.

Video of Coolant Temperature Sensor