Coolant level light is ON 
Coolant level sensor advice
Teching In
Joined: Jun 2011
Posts: 16
Likes: 1
From: Sydney Australia
Heaps of info but no closer to solution thanks GM Well I found the information on these suckers and when I checked the flow chart from the original workshop manual it points to the sensor being the problem (unless I have an air pocket around my sensor probe).
Manual Update /Supplement GMP/98-F-UPD
page 8A-81-14 chart #10
LOW COOLANT LEVEL INDICATION INOPERATIVE (V8VIN G)
TURN IGN KEY TO RUN THEN OFF
DISCONNECT COOLANT LEVEL INDICATOR MODULE (PLUG ON SENSOR)
TURN IGN TO RUN ENGINE OFF
IS THE COOLANT LEVEL INDICATOR ON ?
IF NO AND MINE WAS OFF.
TURN IGN KEY OFF
BACKPROBE WITH FUSED JUMPER FROM CONNECTOR C200D TERMINAL A17 TO GROUND YELLOW AND BLACK CABLE (SAME AS THE CABLE ON THE SENSOR CONNECTION PLUG). THIS IS A LARGE CABLE CONNECTION BLOCK UNDER DASH NEAR STEERING COLUMN.
TURN IGN KEY TO RUN ENGINE OFF
IS THE COOLANT LEVEL INDICATOR ON ? MINE WAS.
IF IT IS, THE MANUAL STATES "REPAIR OPEN OR POOR CONNECTION IN CIRCUIT 68 BETWEEN C200A AND ENGINE COOLANT LEVEL INDICATOR MODULE." IS THE REPAIR COMPLETE ? MINE WAS NOOOOOO!
OK I HAD A THINK ABOUT THIS AND A FEW WILD TURKEYS (BOURBON) AND THOUGHT TO MYSELF THAT IF I NOW DISCONNECT THE SENSOR CABLE AND SHORT OUT THE PLUG PIN THAT GOES TO A17 TO EARTH IT SHOULD REPRODUCE THE SIMULATED FAULT TO THE LOW WATER LIGHT. IT DID, SO THE CABLE IS OK FROM THE CONNECTOR TO THE LARGE CONNECTION BLOCK.
AT THIS POINT I SHOULD POINT OUT THERE IS A BODY CONTROL MODULE CONNECTED TO THE SENSOR AS WELL, ITS JOB IS TO LATCH THE SIGNAL FROM THE SENSOR UNTIL YOU STOP THE MOTOR AND THEN IT RESETS WAITING FOR THE NEXT TIME THE MOTOR IS STARTED.
SO WHAT DOES THIS ALL COME DOWN TOO ?
THE NEW LEVEL SENSOR MUST BE SWITCHING "ON" EVEN WHEN THE WATER/COOLANT IS OK, OR THERE IS A POCKET OF AIR AROUND MY SENSOR, I AM GOING TO BORROW THE FLEXIBLE INSPECTION CAMERA FROM WORK AND SEE IF I CAN HAVE A LOOK IN THE RADIATOR AND INSPECT THE PROBE FOR THIS CONDITION.
AM I GOING TOO FAR
Manual Update /Supplement GMP/98-F-UPD
page 8A-81-14 chart #10
LOW COOLANT LEVEL INDICATION INOPERATIVE (V8VIN G)
TURN IGN KEY TO RUN THEN OFF
DISCONNECT COOLANT LEVEL INDICATOR MODULE (PLUG ON SENSOR)
TURN IGN TO RUN ENGINE OFF
IS THE COOLANT LEVEL INDICATOR ON ?
IF NO AND MINE WAS OFF.
TURN IGN KEY OFF
BACKPROBE WITH FUSED JUMPER FROM CONNECTOR C200D TERMINAL A17 TO GROUND YELLOW AND BLACK CABLE (SAME AS THE CABLE ON THE SENSOR CONNECTION PLUG). THIS IS A LARGE CABLE CONNECTION BLOCK UNDER DASH NEAR STEERING COLUMN.
TURN IGN KEY TO RUN ENGINE OFF
IS THE COOLANT LEVEL INDICATOR ON ? MINE WAS.
IF IT IS, THE MANUAL STATES "REPAIR OPEN OR POOR CONNECTION IN CIRCUIT 68 BETWEEN C200A AND ENGINE COOLANT LEVEL INDICATOR MODULE." IS THE REPAIR COMPLETE ? MINE WAS NOOOOOO!
OK I HAD A THINK ABOUT THIS AND A FEW WILD TURKEYS (BOURBON) AND THOUGHT TO MYSELF THAT IF I NOW DISCONNECT THE SENSOR CABLE AND SHORT OUT THE PLUG PIN THAT GOES TO A17 TO EARTH IT SHOULD REPRODUCE THE SIMULATED FAULT TO THE LOW WATER LIGHT. IT DID, SO THE CABLE IS OK FROM THE CONNECTOR TO THE LARGE CONNECTION BLOCK.
AT THIS POINT I SHOULD POINT OUT THERE IS A BODY CONTROL MODULE CONNECTED TO THE SENSOR AS WELL, ITS JOB IS TO LATCH THE SIGNAL FROM THE SENSOR UNTIL YOU STOP THE MOTOR AND THEN IT RESETS WAITING FOR THE NEXT TIME THE MOTOR IS STARTED.
SO WHAT DOES THIS ALL COME DOWN TOO ?
THE NEW LEVEL SENSOR MUST BE SWITCHING "ON" EVEN WHEN THE WATER/COOLANT IS OK, OR THERE IS A POCKET OF AIR AROUND MY SENSOR, I AM GOING TO BORROW THE FLEXIBLE INSPECTION CAMERA FROM WORK AND SEE IF I CAN HAVE A LOOK IN THE RADIATOR AND INSPECT THE PROBE FOR THIS CONDITION.
AM I GOING TOO FAR
Teching In
Joined: Jun 2011
Posts: 16
Likes: 1
From: Sydney Australia
need smaller camera Camera in radiator would not fit 
No gunk as this is a new sensor from Rockauto, just put it in. Have just done a flush of old coolant and put new coolant in 50/50 burped air out of system with heater on, all good. Temperature runs normal and checked radiator level many times and always at the top of neck. When checking Temp. I am looking at the car gauge in dash which shows just under 100 deg C but have used a Temp hand held Temperature gun to check at the top of the radiator, it shows about 85 deg C. so I think all is ok there. I was going to use a submersible camera to see if there was an air bubble around the sensor, but will not fit down the radiator .
I checked the cable going to the cable connector C200A and the other side of this connector is C200A terminal A17 its a yellow/black cable from sensor, all ok no short and not open circuit.
1 If I take off the connector to the level sensor the light will not go on.
2 If I simulate the fault condition by shorting the yellow/black wire at the connector for the sensor the light goes on. This to me shows to me the circuit operation is ok or could it be it is looking for a different reading from the new sensor. What I mean to say is this probe I think is a Thermistor and therefore changes resistance, GM used a negative temp coefficient type I think.
Has anyone ever taken out the epoxy out of the back of these units and had a look inside them ????
This is getting very confusing
O yer the Light goes on when initial start sequence is started as it should to check lamps, then it goes off. But it only takes about 5 to 10 seconds and it comes back on, once this happens the Body Control Module will latch it on to warn driver of a fault condition until car is turned off and started again, this is the normal operation for this part of the circuit operation.
Graeme in OZ
No gunk as this is a new sensor from Rockauto, just put it in. Have just done a flush of old coolant and put new coolant in 50/50 burped air out of system with heater on, all good. Temperature runs normal and checked radiator level many times and always at the top of neck. When checking Temp. I am looking at the car gauge in dash which shows just under 100 deg C but have used a Temp hand held Temperature gun to check at the top of the radiator, it shows about 85 deg C. so I think all is ok there. I was going to use a submersible camera to see if there was an air bubble around the sensor, but will not fit down the radiator .
I checked the cable going to the cable connector C200A and the other side of this connector is C200A terminal A17 its a yellow/black cable from sensor, all ok no short and not open circuit.
1 If I take off the connector to the level sensor the light will not go on.
2 If I simulate the fault condition by shorting the yellow/black wire at the connector for the sensor the light goes on. This to me shows to me the circuit operation is ok or could it be it is looking for a different reading from the new sensor. What I mean to say is this probe I think is a Thermistor and therefore changes resistance, GM used a negative temp coefficient type I think.
Has anyone ever taken out the epoxy out of the back of these units and had a look inside them ????
This is getting very confusing
O yer the Light goes on when initial start sequence is started as it should to check lamps, then it goes off. But it only takes about 5 to 10 seconds and it comes back on, once this happens the Body Control Module will latch it on to warn driver of a fault condition until car is turned off and started again, this is the normal operation for this part of the circuit operation.
Graeme in OZ
Teching In
Joined: Jun 2011
Posts: 16
Likes: 1
From: Sydney Australia
Experiment done see results I have just conducted my own Experiment on sensor and sensor circuit.
I said before that this sensor looks to be a thermistor encased in epoxy resin.
The original Manual has a fault diagnosis chart to test the fault conditions that may occur such as it being on all the time or not on ever. I followed the instruction to find out why my low coolant light came on after 10 seconds or so once motor started.
If coolant level indicator inoperative (V8 Vin G)
It said to turn off motor turn off ignition, then unplug sensor. Is the light on when you then turn ignition switch on, motor off ?. Mine was off.
It said if off then check the connection point on the large connection block under dash C200D by using a fused jumper from terminal A17 to ground.
Turn the ignition switch to Run motor off. Is the lamp on ? If yes check for poor connection in circuit circuit 68 between C200A and engine coolant level sensor.
If low coolant level is always On (V8 Vin G) and this is my problem and many others.
Turn ignition switch to run then off.
Disconnect coolant level indicator module.
Turn on the ignition switch to run, motor off.
Is the engine coolant light On ? Mine was Off.
If off Replace engine coolant level indicator module (sensor)
That is there fault diagnosis chart explanation in condensed form see
Page 8A-81-14 and 8A-81-15 Charts 10 and 11
Service Manual "Update/Supplement" GMP/98-F-UPD
Ok now I have checked my cable and replaced Level Sensor and replaced Radiator Cap, flushed system and replaced coolant ratio 50/50.
Still the light comes on after 10 or so seconds from start.
I removed plug from sensor and shorted the Yellow/black stripe cable to ground, light comes ON. This is correct.
I connected the sensor to a multimeter and found it to be around
14Meg ohms across the two pins one way, and infinite resistance the other.
Then I exposed the probe on the sensor to a heat source and found the resistance was slowly dropping, this is what I expected from a Negative Temperature Coefficient (NTC) Thermistor. The resistance would drop as the probe heated when the water was not around the probe. At a certain resistance around 180 ohms the light will turn ON and stay on due to being latched by the Body Control Module, this is a normal operation to warn driver there is a low coolant condition. It will not reset until car is turned OFF and restarted and coolant topped up. Or replacement sensor is installed. But in my case it looks like my new sensor from RockAuto is FAULTY .
Noticed when I got it in the mail it was made in "TAIWAN" I think could this have any bearing on the quality of this product ???
I got the resistance value by putting a 200k ohm variable resistor on the plugs two connections that goes to the sensor (sensor not in circuit) turned it up to max the turned ignition to Run motor off, this slowly reduced the resistance until the lamp came ON which I said was around 180 ohms.
Anyway hope this helps you guys out there, and if you see any flaws in my post, let me know, but please have some proof as I have spent about 8 hours working this out
.
Now hope the return postage to USA is not too expensive
Graeme in OZ
I said before that this sensor looks to be a thermistor encased in epoxy resin.
The original Manual has a fault diagnosis chart to test the fault conditions that may occur such as it being on all the time or not on ever. I followed the instruction to find out why my low coolant light came on after 10 seconds or so once motor started.
If coolant level indicator inoperative (V8 Vin G)
It said to turn off motor turn off ignition, then unplug sensor. Is the light on when you then turn ignition switch on, motor off ?. Mine was off.
It said if off then check the connection point on the large connection block under dash C200D by using a fused jumper from terminal A17 to ground.
Turn the ignition switch to Run motor off. Is the lamp on ? If yes check for poor connection in circuit circuit 68 between C200A and engine coolant level sensor.
If low coolant level is always On (V8 Vin G) and this is my problem and many others.
Turn ignition switch to run then off.
Disconnect coolant level indicator module.
Turn on the ignition switch to run, motor off.
Is the engine coolant light On ? Mine was Off.
If off Replace engine coolant level indicator module (sensor)
That is there fault diagnosis chart explanation in condensed form see
Page 8A-81-14 and 8A-81-15 Charts 10 and 11
Service Manual "Update/Supplement" GMP/98-F-UPD
Ok now I have checked my cable and replaced Level Sensor and replaced Radiator Cap, flushed system and replaced coolant ratio 50/50.
Still the light comes on after 10 or so seconds from start.
I removed plug from sensor and shorted the Yellow/black stripe cable to ground, light comes ON. This is correct.
I connected the sensor to a multimeter and found it to be around
14Meg ohms across the two pins one way, and infinite resistance the other.
Then I exposed the probe on the sensor to a heat source and found the resistance was slowly dropping, this is what I expected from a Negative Temperature Coefficient (NTC) Thermistor. The resistance would drop as the probe heated when the water was not around the probe. At a certain resistance around 180 ohms the light will turn ON and stay on due to being latched by the Body Control Module, this is a normal operation to warn driver there is a low coolant condition. It will not reset until car is turned OFF and restarted and coolant topped up. Or replacement sensor is installed. But in my case it looks like my new sensor from RockAuto is FAULTY .
Noticed when I got it in the mail it was made in "TAIWAN" I think could this have any bearing on the quality of this product ???
I got the resistance value by putting a 200k ohm variable resistor on the plugs two connections that goes to the sensor (sensor not in circuit) turned it up to max the turned ignition to Run motor off, this slowly reduced the resistance until the lamp came ON which I said was around 180 ohms.
Anyway hope this helps you guys out there, and if you see any flaws in my post, let me know, but please have some proof as I have spent about 8 hours working this out
.Now hope the return postage to USA is not too expensive
Graeme in OZ
Last edited by graemer66; Aug 31, 2011 at 06:33 AM.
Teching In
Joined: Jun 2011
Posts: 16
Likes: 1
From: Sydney Australia
standing in front of the car, the sensor is on the left side of the radiator about 4 inches down. It's a rectangular box that uses a wire clip to keep it on. You can try to pry the clip open a bit, or just give it a good pull if that doesn't work. Once you pull it out you will leak coolant, so be prepared for that.
I replaced mine when it started incorrectly indicating low coolant. The replacement worked for about 3 months, and then started reading incorrectly again. I just disconnected the cable and check the level manually.
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Joined: May 2006
Posts: 3,452
Likes: 3
From: somewhere that doesn't get snow
i'm going through this myself and tried replacing the sensor. i must have gotten a dud because the new sensor wouldn't even turn the light on for the key on bulb test. my old sensor had the exact opposite problem as it would keep the light on for no reason. i ended up returning the new sensor and put the old one back in and kept it unplugged for now. my radiator is full and never was low during the "low coolant" light coming on. sometimes if i turned the key on and off a few times i could get the light to come on normally and then shut off (with the old sensor)
