What does it mean when the DEF light in a car comes on?
2 Answers
When the DEF light in a car comes on, it indicates that the auxiliary water tank is low on water. If the DEF is displayed as a small mileage reading on the instrument panel, it suggests an internal processor fault in the instrument cluster. Below are some methods for checking internal instrument faults: 1. Tap and Press Method: This can be used to diagnose the issue, as most faults are caused by poor contact or soldering problems. 2. Comparison Method: This requires two identical instrument clusters, with one functioning normally. Compare the voltage, waveform, static impedance, output results, and current of the instrument clusters. If these are all normal, the issue might be with the instrument's signal. If the signals differ, the fault likely lies here, and professional repair is needed.
The DEF light most commonly appears on diesel vehicles, indicating that the Diesel Exhaust Fluid (DEF), also known as AdBlue, is running low. If not refilled promptly, the engine's power will be restricted—you won't be able to accelerate even when flooring the throttle, and in severe cases, the vehicle might just shut down on you. As a long-haul trucker, this is my worst nightmare during cargo runs. The light typically goes off after topping up the DEF tank at a service station. In some models, this light might flash alongside the engine malfunction indicator, signaling a system blockage or sensor malfunction, which requires an immediate trip to the repair shop for diagnostic trouble code reading. Regularly checking the DEF tank level can save you a lot of hassle.
