Nitrite is a common corrosion inhibitor in coolants, but its level can be reduced over time through oxidation or consumption. Too low nitrite level means reduced corrosion protection.
Nitrite is measured color photometrically or chemically with the test reagent, giving an accurate impression of its concentration.
The result gives the customer insight into the fluid's ability to prevent rust and corrosion, and whether a refill or full replacement is needed.