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Thread: Coolant Temperature Sensor

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Posts: 1-10 of 125
2009-11-13 18:16:07
#1
Coolant Temperature Sensor
On the side of the intake there's 2 fun little coolant sensors, one is the 2-plug "coolant temp sensor" and the other is the one-plug "thermal transmitter" that runs the gauge.

The thermal transmitter works fine, and the gauge reflects as such. The coolant temp sensor though seems to be acting weird. Due to swapping in a highport after having a lowport, the connection for this guy was different and I manually wired it up.

With it hooked up, my radiator fans simply don't kick on, and I've had the car nearly overheat a few times from this. If I leave it unplugged, though, the fans are constantly on and I think the computer reverts to a "default" mode they describe in the FSM, which means the fans are always on and the injectors are pulsed simultaneously 2 times each cycle.

My concern here is, the car obviously doesn't run well and has trouble starting up cold because of the injector pulses being odd with the sensor unplugged. I have it that way since I feel safer knowing the fans are always on than trying to deal with it overheating again.

From what I saw, it's not really possible to wire the coolant temp sensor backwards as it's a resistor. So, since it's a 1997 vehicle running a 1993 engine and sensors, is the coolant temp sensor different in a 93 than a 97? Are it's resistance readings different than the 97's at different temperatures and the computer simply doesn't know how hot the engine really is?
2009-11-13 18:58:34
#2
Originally Posted by WingmanSR20
So, since it's a 1997 vehicle running a 1993 engine and sensors, is the coolant temp sensor different in a 93 than a 97? Are it's resistance readings different than the 97's at different temperatures and the computer simply doesn't know how hot the engine really is?


93 ECTS is different than the 97 ECTS.
The OEM sensors are different colors too I think.
Look on rockauto.com, they list different part numbers for 93 vs 97.
Listed under cooling system, coolant temp sensor (NOT sender).
2009-11-13 19:05:38
#3
Yes, they are different colors and different connectors, but according to the FSMs they're the same thermistor and react identically to the same temperatures. The only difference is the connector plug to the harness.
2009-11-13 19:48:47
#4
Originally Posted by WingmanSR20
Yes, they are different colors and different connectors, but according to the FSMs they're the same thermistor and react identically to the same temperatures. The only difference is the connector plug to the harness.


Yes, you are correct:
'97 SR20DE ECT (EngineCoolantTemperature) Sensor:
14 F - 4.4 volts - 9.2 kOhms
68 F - 3.5 volts - 2.1 - 2.9 kOhms
122 F - 2.2 volts - 0.68 - 1.00 kOhms
194 F - 0.9 volts - 0.236 - 0.260 kOhms

'93 SR20DE ECT:
68 F - 2.1 - 2.9 kOhms
122 F - 0.68 - 1.0 kOhms
176 F - 0.30 - 0.33 kOhms

Polarity should not matter for a thermistor.
Maybe the sensor is bad?
I tested the resistance of mine, submersed in cold and hot water,
around the temps listed in FSM to see if it was bad.

I think I have a spare highport & lowport sensor - I'll have to look...
2009-11-13 21:20:28
#5
hmm, well for now im wiring the fans to my unused AC switch above the radio. I'll just have to watch the temp gauge and kick them on manually. The computer seems to adjust fuel properly for the engine's temp for running. I'll test the sensor's resistance later once it's cooled back down to air temp.
2010-01-10 14:47:06
#6
I have almost the exact same problem but i have a 96 200 running a JDM RR with an obd1 harness.... do i need to find b13 temp sensors to fix this? i wasnt aware that this would affect my fueling also. will this cause the car to run a little more lean?!?!
2010-01-10 15:34:36
#7
No, it'd cause the car to run rich.

You need the CTS that matches your ECU. If you have a 96 USDM ECU with harness, use the 95+ CTS.

If you're running an OBD1 ECU and harness, you need the OBD1 CTS.
2010-01-11 03:05:51
#8
yea thats what i meant! lol my car pops and backfires in between shifts, or on decel. this has to be my problem! thanks mang!
2010-01-11 04:35:25
#9
Originally Posted by Phat_sx
yea thats what i meant! lol my car pops and backfires in between shifts, or on decel. this has to be my problem! thanks mang!


You may also have a close exhaust leak before the cat, this will cause those exact symptoms as well. I'm ofc assuming you mean backfiring out the exhaust, not the intake.
2010-01-11 04:42:15
#10
just out of curiosity, did you use thread tape when you put the sensor in??
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