1999 Pontiac Grand Prix low coolant light

Tiny
JR47
  • MEMBER
  • 1999 PONTIAC GRAND PRIX
  • 3.8L
  • V6
  • FWD
  • AUTOMATIC
  • 205,713 MILES
For the past week my low coolant light has been turning on and off and I have checked the coolant level several times both hot and cold levels and it was right on where it needs to be but there was only one time when I actually needed to add coolant but I only had to add a small amount of it. If you need to know the time when it needed coolant was for the hot level indicator. Any idea on what's going on here?
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Saturday, June 20th, 2015 AT 12:28 AM

8 Replies

Tiny
CARADIODOC
  • EXPERT
Most likely the float has sunk in the reservoir. I'm not sure how it is removed but I suspect it can be replaced without having to replace the entire reservoir. You can unplug the switch to verify there isn't some other wiring problem.
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Saturday, June 20th, 2015 AT 12:32 AM
Tiny
WRENCHTECH
  • EXPERT
Ho Doc

The coolant level sensor in this car is not a float and it's not in the reservoir. It's a liquid sensor that is in the radiator so the first thing to do is verify the coolant level in the radiator, not just the reservoir. This type of sensor does fail quite often so that could be your problem also. It snaps into the radiator.

https://www.2carpros.com/images/external/78447601.jpg.gif
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Saturday, June 20th, 2015 AT 5:33 AM
Tiny
WRENCHTECH
  • EXPERT
That was supposed to be Hi not Ho Doc. LOL
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Saturday, June 20th, 2015 AT 5:34 AM
Tiny
CARADIODOC
  • EXPERT
Dandy. Thank you for setting me straight. I've never run into this one before.

You're truly a wonderful human being!
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Saturday, June 20th, 2015 AT 9:36 PM
Tiny
WRENCHTECH
  • EXPERT
It's a 3 wire sensor that shares the same reference voltage as most other sensors and I've had them get shorted and cause some real driveability problems by pulling down the reference voltage for some vital sensors.
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Sunday, June 21st, 2015 AT 3:47 AM
Tiny
JR47
  • MEMBER
Ok guys the light went on and off again yesterday and I did check both levels in the radiator and the reservoir and both were full. But one thing I found is that there is some type of sludge build up on the inside of the filler neck of the radiator and under the radiator cap itself. I have a photo of it and ill try to upload it. If the photo didnt upload the sludge stuff is a very light brown almost tanish in color, plus its not really thick its actualy a thin layer of it.
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Wednesday, June 24th, 2015 AT 1:02 PM
Tiny
CARADIODOC
  • EXPERT
I doubt that's the issue. Look for the sensor that Wrenchtech mentioned.
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Thursday, June 25th, 2015 AT 12:55 AM
Tiny
WRENCHTECH
  • EXPERT
It is possible that the sludge or whatever that stuff is s coated the sensor probes, making it deliver faulty readings. You need to find out what that stuff is. It could be leaking trans fluid due to a bad cooler in the radiator.
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Thursday, June 25th, 2015 AT 1:59 AM

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