What is the reason for the urea tank not making noise after parking?
3 Answers
When there is no noise after parking, it indicates a malfunction in the urea pump. The urea pump continues to operate after the engine is turned off to return the unused urea in the pipes back to the urea tank. Otherwise, the urea in the pipes may crystallize, affecting normal use during the next operation. Therefore, the urea pump continues to work for a while after the vehicle is turned off before stopping automatically. Below is an introduction to the urea pump: 1. Working principle and internal composition of the urea pump The urea pump is the core component of the SCR system, known as the "urea dosing pump." Its main function is to pump the urea solution from the urea tank and transport it to the nozzle through the delivery pipe. 2. Working principle of the urea pump The internal composition of the urea pump mainly consists of a diaphragm pump, electromagnetic reversing valve, pressure sensor, urea filter, electric heating system, lead frame, and other components. The exterior is composed of three urea solution pipelines: the spray pipe, return pipe, and inlet pipe. 3. Internal composition of the urea pump There are two types of urea pumps: one is the airless urea pump represented by Bosch, and the other is the air-assisted urea pump represented by Emitec and Cummins.
I've been driving a diesel car for five years, and I noticed right after buying it that the urea tank doesn't make any noise after parking. It took asking quite a few friends to figure it out. That pump in the urea tank only works when the engine is running or when the system needs it. After parking and turning off the engine, the entire SCR system takes a break and doesn't need to operate at all, so it's perfectly normal for it to be silent. I initially thought it was a malfunction and worried unnecessarily a few times. If you don't hear any sound while driving either, then you need to check for reasons, like a stuck pump or a short circuit in the wiring, which can trigger the malfunction light. It's crucial to regularly top up the urea solution and not let it run empty. In short, silence after parking is completely fine; just pay attention to its performance while driving, and if there's an issue, get it fixed early.
Having worked in the automotive repair industry for over twenty years, I've encountered numerous urea system issues. If there's no sound after parking, it's usually fine—the pump naturally stops when the engine is off. However, if there's no noise while driving, you should be alert: it could be due to an aged or burnt-out pump motor, poor wiring contact or loose plugs, a stuck or malfunctioning relay switch, or an error in the control module. Sometimes, incorrect urea concentration or freezing can also cause faults. I typically start by using a diagnostic tool to read the fault codes for troubleshooting. I advise users not to ignore this issue, as it relates to emission regulations. Neglecting it could lead to vehicle speed limitation, warning lights turning on, and compromised driving safety—prompt repair is essential.
