coolant sensor reading 115 degrees cold or hot

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  #1  
Old 07-10-03, 11:14 AM
Ghilsenb
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coolant sensor reading 115 degrees cold or hot

Have a 1994 dodge caravan, 170,000 miles and the check engine light came on and took it to the shop and had diagnostic ran. Was told main computer was bad and that coolant sensor was bad as it was telling to computer that it was 115 degrees when the engine was cold or hot. Replaced main computer, and coolant sensor. Runs better, but still getting the 115 degree readout, tried new coolant temp sensor- same read out.

The Radiator fan is running all the time too. Checked relay, reads good. When I first start it, it takes a minute for it to run smooth, checked fuel pressure regulator was OK. Any ideas what might be the problem or next step to take.
 
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  #2  
Old 07-10-03, 11:24 AM
Joe_F
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Who replaced the parts? If it was the shop, bring it back--sounds like they didn't fix your problem.

Are you stating that the scan tool always reads the temperature at 115 degrees or the gauge on the dash reads cold?
 
  #3  
Old 07-10-03, 12:06 PM
Ghilsenb
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The scan is showing the 115 degree temp and the only problem showing up on the scan is the coolant temperature sensor, giving the reading of 115 degrees hot or cold. I replaced the coolant temp sensor twice and checked it and it is a good sensor.
 
  #4  
Old 07-10-03, 12:25 PM
Joe_F
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What brand of sensor is being used?
 
  #5  
Old 07-10-03, 12:43 PM
Ghilsenb
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Wells and GP Sorenson is the brand of the sensor
 
  #6  
Old 07-10-03, 01:42 PM
Joe_F
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Try an OEM one just to be sure you didn't get two defects or one that's really out there .
 
  #7  
Old 07-10-03, 05:45 PM
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Not to be a pain, but are you (ot the shop you took it to) changind the temp sensor, or the temp sender? It wouldn't be the first time I've seen them get confused...Sender is for the gauge, sensor feed the computer..Many look similiar...

Just a thought...
 
  #8  
Old 07-10-03, 05:55 PM
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did you ever hear of 'ohming' wires---measuring them for resistance, i would start with the two that go from the sensor to the computer. when the coolant sensor is unplugged, it causes the fan to run continuously(as a safety measure). you can also have an overanxious parts counterperson trying to sell you the wrong sensor twice, a lot look the same, but the calibrations(internal resistance) can be very different, causing your problem.

take a flashlight and look into the connector and see if one terminal is even a hair bigger than the other, squeeze them both smaller anyway to get a better connection, any green corrosion at all will cause this problem too-- in any of the connectors between the sensor and computer, as will wires laying on the exhaust crossover pipe(V6)


if the 'mechanic' is using a scan tool, the easiest way to check the wiring and computer is to watch the voltage on the scan tool, unplug the sensor, voltage should be 5.0 volts, jump the two pins with a paper clip, the voltage should be 0.0 volts(or the opposite--0.0 unplugged,5.0 jumpered)this will NOT hurt anything, it can only be a sensor then(or connector at the sensor)



ps. what engine?
 
  #9  
Old 07-10-03, 05:59 PM
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good point mr sargent, the sensor for the computer has two wires, the one for the guage/light inside the car has one wire, i have seen that too!
 
  #10  
Old 07-10-03, 11:23 PM
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Does kinda sound like a wiring problem...possibly in the connector, because the fan should not come on until the sensor reads 212 degrees. If the sensor is unplugged or not making connection, the fan will run continuously, as mentioned.
 
  #11  
Old 07-11-03, 06:35 AM
Joe_F
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Thumbs up

Good advice from everyone.
 
  #12  
Old 07-11-03, 07:07 AM
Ghilsenb
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Mike- thanks for the tip on the connectors, took the sensor off, squeezed the connectors in a bit and plugged it back in and it fixed the problems with the fan and the check engine light went off. Thanks a million for all the suggestions folks
 
  #13  
Old 07-11-03, 07:59 AM
Joe_F
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Thumbs up

Good job and glad you got it fixed.
 
  #14  
Old 07-11-03, 10:33 PM
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and also THANK YOU for posting to everyone else here what actually fixed it, that does help all of us!
 
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