On August 11th, 2004, General Motors released technical service bulletin # 04-06-02-007 in regards to numerous complaints of the coolant light staying on in various makes and models, including the 2000 to 2002 Chevy Impala. The cooling system in your impala holds just under three gallons of a 50-50 mix of Dexcool and distilled water. Because it is necessary to maintain a healthy engine cooling system, a coolant level sensor was installed in the radiator to alert the driver the cooling system is low. If your low coolant light is on there are several reasons and a strait forward way to solve the problem.
The first thing yous should do regarding an illuminated low coolant light is to check your coolant level and verify it is between the hot full and cold full lines on the coolant reservoir, depending on the temperature of the engine. If the coolant level is low, top it off with fresh 50-50 premixed Dexcool. Note, the coolant system is sealed and any “use” of coolant indicates a problem somewhere in the system. If the system hasn't been recently serviced, inspect coolant hoses for leaks, the tail pipe for signs of coolant and the engine oil for signs of coolant contamination; repair anything leading to the loss of coolant immediately . If the coolant level is full, but the system was just recently serviced or flushed it is possible there is an air pocket in the system causing a false warning light. If service was recently performed, properly fill and bleed the cooling system before any performing any further testing.
Turn the key to the “On” position, but do not start the engine. Squeeze the tab on the coolant sensor electrical connector and disconnect the harness from the connector. If the low coolant light remains on, there is a short in the chassis wiring harness or the instrument cluster. Inspect the wiring for the for the low coolant sensor and the wires leading to the instrument cluster and repair any wiring as necessary. If there are other problems within the instrument cluster like inoperable gauges or lights, it is likely the instrument cluster should be replaced. Diagnose the instrument cluster for failure and replace as necessary.
Chevy recommends not using any type of coolant system additive in your cooling system. Some after market cooling additives can leave an oily residue throughout the cooling system, including the coolant level sensor. An oily residue on the level sensor will cause a false reading that leads the computer to improperly illuminate the low coolant light. If any additives have been used, flush the cooling system and remove the level sensor for cleaning. Fill the system with fresh 50-50 Dexcool and check for proper operation of the low coolant light. If any type of sealant additives have been used, repair the leak properly before flushing the system.
Engine oil in your coolant system will coat the coolant level sensor and cause the coolant light to illuminate incorrectly, among other problems. Inspect the color and texture of the coolant in the radiator. Engine oil contamination can range from a light sludge coating through out the system or in extreme cases milky fluid throughout the cooling system that will be noticeable in the overflow bottle and radiator fill neck. In most cases, when you find engine oil in the coolant system you will also find coolant contamination in the engine oil. If you are experiencing oil in your coolant it is possible the engine has a blown head gasket causing the coolant and oil to mix, which may result in excessive white smoke from the exhaust system. If your impala is equipped with an oil cooler, the radiator may have internal damage between the oil cooler portion and the coolant portion of the radiator causing the contamination. To check for internal radiator damage, disconnect the oil cooler lines and connect them together with the proper sized coupler, then flush the oil and cooling system. If contamination is no longer present after normal operation, replace the radiator and reconnect the oil cooler lines. If the source of contamination is the result of a blown head gasket diagnose and replace the faulty head gasket and intake manifold gaskets.
Partially drain the cooling system so the level will be below the level sensor. Disconnect the level sensor harness. Lift the left leg of the retaining clamp and pull the sensor from its fitting with a slight twisting motion. Spray the tip of the sensor with brake cleaner and clean the sensor with a wire brush. Wash away any remaining deposits from scrubbing with brake cleaner and install the level sensor. Check for proper operation.
