1998 Civic EX Sedan D16Y8

Are there three coolant temperature sensors on my D16Y8 engine?
There is one near the thermostat housing, which is a switch to turn the radiator fan on and off.
There is a second one, easy to reach, near the distributor, and it has a two-wire connector.
There is a third one below the distributor, hard to reach, with a single-wire connector.

A mechanic told me the second one just feeds the dashboard temperature gauge, and the third one provides the signal that the computer uses for engine control. Does that sound correct? He called the third one the TW sensor, which I have never heard of.

Thanks for any enlightenment you can provide.

 

Part #11 is the "Thermo Unit". It's the one-wire plug, and sends temperate signal to the cluster. Part #12 is the Thermo Switch assembly, and tells the fan when to turn on. Part #13 is the Water Temperature Sensor assembly, and tells the ECU how hot the motor is.

 

Thank you very much. Makes sense. Apparently the mechanic had the functions of #11 and #13 mixed up.

I do have a weird problem with temperature – maybe you can help some more?
When I start the engine cold, idle speed is appropriate, about 1800 RPM. If I then drive a few miles, the engine warms up normally, plenty of heat from the heater, but idle speed stays high and even goes up a little to 2200 RPM. But if I just turn off the key, and turn it back on before the engine dies, idle speed drops to 750-800 RPM. If I shut off and restart the engine only partially warm, idle speed is also appropriate, say 1100 RPM, but even with more driving it doesn’t drop below 1100 until I shut off and restart. IN OTHER WORDS, THE COMPUTER SEEMS TO SET IDLE SPEED PROPERLY BASED ON COOLANT TEMPERATURE AT STARTUP, BUT THEN NEVER ADJUSTS IT FURTHER. Thermostat and IACV and computer have been replaced, with no change in behavior. I have checked the resistance of the ECT sensor (#13) at various engine temperatures, and it is accurate. The car has 286,000 miles. There are no other drivability problems of any sort. Any idea what is wrong?

 

That's a new one on me. Is the CEL on? Does it work? Since you have a voltmeter, double-check the voltage to your IACV, and make sure your TPS is within spec.

 

It's a new one on everybody. No CEL, and yes the light does work. IACV does work, since it does adjust idle speed consistently based on starting temp of the engine.

Interesting that you should suggest the TPS, however. It doesn't set any codes, but I know that is slightly out of spec at throttle-closed, because I tweaked it to (successfully) cure a transmission flare issue between 2nd and 3rd gear. (That's another thread -- in short, I noticed that flare occurred during gentle acceleration, but not at hard acceleration. So by rotating the TPS slightly to simulate harder acceleration, the flare problem went away.) I guess I should put the TPS back to its proper spot and see if the idle issue disappears.

Thanks for the idea.

 

Yeah, you need to pull out your voltmeter and properly set your TPS.