Are they interchangeable parts? They appear to be the same. Anybody know?

 

Hi XJ8JR,

According to the '04 New XJ Technical Introduction dealer training manual, it's difficult to tell, but from the scarce information provided the sensors do not appear to be the same part.

The Engine Coolant Temperature Sensor (ECT) receives a 5V supply from the ECM. Its resistance varies proportionally with coolant temperature. At 20 deg. C it will have a nominal resistance of 2.45 Kohms and the voltage across the sensor will be 2.38V.

The Engine Fuel Temperature Sensor (EFT) also receives a 5V supply from the ECM. Its resistance range is 1 to 95 Kohms and the voltage across the sensor ranges from 0.2 - 3.8V. The ECM uses its signal to adjust fuel pump pressure to prevent vaporization and ensure adequate fuel supply to the injectors.

The EPC shows different part numbers for the two sensors, and jaguarmerriamparts.com shows different prices:

Coolant Temp Sensor LNA1600AA $44.07

Fuel Temp Sensor LRA1600BA $42.51

Rock Auto carries the CTS, but does not list the FTS.

My guess is that the sensors are similar, but that their resistance ranges are different. The manual does not say, but it's even possible that the EFT's resistance operates in the opposite direction compared to the ECT, falling with increasing temperature (i.e. it may be a negative temperature coefficient (NTC) thermistor).

You could test them manually with an ohmmeter and a pan of water. Measure their DC resistances at room temperature, then dip the sensor tips in a pan of hot water for several seconds and measure the resistances again and compare the results for both sensors.

Cheers,

Don

 

That answers my question! Thank you so much, Don

 

Not only are the resistance values different but the connector has different splines preventing you from plugging in the wrong one.