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Coolant Temp Sensor Behavior

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1 It does not start when cold.

2 Is well described in the thread above. Erratic idling and running.

worth your while to read the other threads on this. looks pretty easy to replace on my car.

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My car is doing the exact same thing, hard starting when its cold, and erattic idle, etc... 1992 legacy.

Did this give you any codes, ?

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What happened in my case is (1) it would'nt start when hot (Ecu was receiving the info that the engine was cold and flooded it) (2) i also had at one point the erratic idle symptom that led to stalling and impossibility to restart.

When this happens it usually possible to start the car either by waiting for the excess fuel to evaporate (at least 30 minutes) or by pushing the gas pedal to the floor while starting. This gives the engine more air and can get rid of excess fuel if the condition is not hopeless.

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sounds all too similar.

However...I have replaced, several other sensors...not inccluding these and still have NO codes, but the car runs horrible....hardly back out of the garage but runs. when parked...

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Originally posted by Tricky

My car is doing the exact same thing, hard starting when its cold, and erattic idle, etc... 1992 legacy.

Did this give you any codes, ?

 

Yes, the codes it spits out are:

-11-Crank Angle sensor or circuit

-12-Starter switch or circuit

-13-Cam Position sensor or circuit

-21-Coolant Temperature sensor or circuit

-42-Idle swich or circuit

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You can get a rough idea without removing it if you can get the meter wires connected successfully. It is probably easier to just take it out.

 

If you want to test it in the car: Let the car sit long enough to cool completely. Overnight would be best. Measure the ambient temperature. Take a resistance measurement of the sensor. Reconnect the sensor and warm the car up until the both radiator hoses are warm along their entire length. That should put your temp fairly close to the thermostat temperature. Shut it off and take another reading.

 

From Haynes:

     Temp*F                     Ohms------------------------------------     212                        176     194                        240     176                        332     158                        458     140                        668     122                        972     112                       1182     104                       1458      95                       1800      86                       2238      76                       2795      68                       3520      58                       4450      50                       5670      40                       7280      32                       9420

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Another quick thing....The cooling fans come on immediately when the key is turned to the on position. Is this a good sign of the ECT sensor or is it the ECU going into a failure mode?

Thanks in advance,

Shawn

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Sounds like a bad coolant temp sensor. The ECU uses the temp reading from the coolant temp sensor to determine when to turn the fan on. It sounds like the ECU thinks the engine is really warm when it is actually cold. That would explain any hard starting you may be experiencing. I would pop the connector off of the ECT with the engine cold, take a measurement, and compare it to the chart I posted.

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I didn't put the fluke meter to it yet, but I unplugged the sensor with the car running and it had no effect whatsoever. Something tells me that if the sensor was any good, it would make the car run differently if unplugged ?

Shawn

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if the sensor was any good, it would make the car run differently if unplugged ?

Good logic if you want my opinion. :wave:

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If the fans are on, the sensor circuit is open or shorted and most likely it's a bad sensor.

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YEP! The Coolant temp sensor was definately bad....Car fired right up after replacing it...

 

I tested the old one for ohm's and got nothing, tested the new one and the ohm's would lower the hotter it got :)

 

THANKS EVERYBODY FOR ALL YOUR AWESOME INPUT!!!

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