Low Coolant light

Not sure what year Elantra you have but most don't have a low coolant light. If you do have one, check for a faulty level sensor.

b0936 - When engine coolant is at the proper level, the low coolant switch is closed. When in this condition, battery voltage is applied to the low coolant 1478 input of the body control module (BCM).
When coolant is below the proper level, the coolant switch opens. Because no voltage is applied to circuit 1478, the BCM responds by sending a serial data message to the instrument panel cluster to turn On the low coolant light.
The BCM has an internal timer, which will not turn On the low coolant telltale unless the coolant level is low for greater than 30 seconds. The timer avoids coolant "sloshing" falsely turning On the light.
B0936 Coolant level sensor circuit malfunction .
Check for poor connection at BCM. Inspect harness connector for backed out terminals, improper terminal mating, broken connector locks, improperly formed or damaged terminals and poor terminal to wire connection (terminal crimped over wire insulation and not conductors).

?€¢
Inspect wiring harness for damage. Check for broken or chafed insulation.

?€¢
Check for poor connection at the low coolant switch.

?€¢
If fault is suspected to be intermittent, wiggling harness wiring may help in locating fault.

B

Where is your coolant going is the biggest problem you have to fix first. You may want to look at the water pump too.

not the pump but air in the system or a broken wire to the coolant level sensor
that sensor at the top of the radiator tank has to be completely immersed in coolant or the circuit is broken and the light comes on
same effect id the wire to that sensor is broken in the insulation

Bleed the air out of the coolant system,and add more coolant,to radiator,and reservoir,and make sure the cooling fans are coming on,if the low coolant light stays on,remove the low coolant light sensor,and clean it off,it is located on passengers side in the radiator,it has a wire clip you have to remove,and dont loose it,after cleaning it,put the clip back on the sensor,and push the sensor back in the hole.

Well, top off the overflow tank to the marks as indicated based on engine temperature, and see if it happens again, and note how long it took for it to happen.

If its not low on coolant and the light continues to come on it is the low coolant sensor in the radiator. This sensor is in the plastic side of the radiator and just pops off. These sensors are always a problem and don't always require replacement of the sensor. What happens -especially if you are using red DEX-COOL coolant is that the coolant gets hard and crusty inside the sensor and wont allow the coolant to enter and make contact with the sensor. Simply take the sensor off and blow compressed air or water pressure in it to free it of debris. Easy fix-hope this helps!

Replace the coolant temp sensor.

I think your buick has a pressure coolant system so you may have air in the system and need too bleed it and for the light coming on while on the highway most likely low coolant when your driving the higher rpm the more coolant is drawn into the motor and triggering the light from coolant reservoir running low on coolant

check for something stuck in the wheels and as for the coolant light get the car running and up to warm temp and start adding coolant to the reserviour bottle until it is up to hot level because there maybe a bubble in the line but also if might be a bad switch in the reservior bottle itself