SCR Solenoid Valve-Function, Design & Benefits

SCR Solenoid Valve Guide for Diesel Systems

SCR Solenoid Valve for Emission Control Systems

SCR Solenoid Valve in Modern Diesel Engines

Efficient SCR Solenoid Valve for DEF Systems

SCR Solenoid Valve--Features and Advantages

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WL171135 Automotive SCR Solenoid Valve Explained

The SCR solenoid valve is a mechanical-electrical switch that regulates the flow of diesel exhaust fluid (DEF) within selective catalytic reduction (SCR) systems. These devices help to reduce NOx emissions in diesel engines by injecting DEF into the exhaust stream. This process initiates chemical reactions that convert toxic gaseous substances into harmless products like nitrogen and water.

The features of SCR Solenoid Valve

The SCR solenoid valve is precision engineered and extremely robust. They provide a rapid reaction and reliable dosing to effectively control emissions. Furthermore, the valves are designed with corrosion-resistant materials that withstand harsh conditions and DEF fluids. In addition, their compact form factor allows them to fit modern engine systems, consume minimal electricity, and have long life spans. In addition, the valves are designed with advanced sealing techniques that prevent leaks and provide high-cycle performance for continuous operation.

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Automotive SCR Solenoid Valve Product Overview

The SCR solenoid valve is a key component of modern diesel engine systems responsible for precise, fast, and reliable NOx reductions. Nevertheless, its performance depends significantly on system design, DEF quality, and maintenance.

It is best suited for applications requiring strict emission compliance, efficiency, and long-term reliability, despite the associated complexity and high costs.

SCR Solenoid Valve Video

Automotive SCR Solenoid Valve Detailed Display

Durable SCR Solenoid Valve for Harsh Environments

SCR Solenoid Valve in NOx Reduction Systems

SCR Solenoid Valve Performance Optimization

SCR Solenoid Valve Buying Guide for Engineers

SCR Solenoid Valve Technical Datasheet

Brand	Weilong Technology	Model Number	WL171135
Rated Voltage (V)	DC 12V or 24V	Rated Power (W)	10-12 W
Media	Hot Water	Holding Force (N)	150 —– 300 GF
Ports:	Dia. 5.1 mm	Reset Time(s)	1 S
Service Life	100 Thousand Times	Certification	CE, RoHS, ISO9001,
Material	Nylon	Lead Wire Length (mm)	200
Install Style	Flange	Tolerance of Dimension	+/- 0.1 MM
Water-proof	IP-68	Insulation Class	B
Hi-Pot Test	AC 600V 50/60Hz 2s	Non-excitation Holding Force	0
Working Temperature	-10°C-100°C	Duty Cycle	1-100%
Working MPa	from 0 to 0.25 Mpa	Payment Term	TT, or LC At Sight
Sample Order	Yes	Warranty	2 Year
MOQ	1000 PCS	Supply Ability	5000 pcs per Week
Delivery Time	30 Days	Port of Loading	shenzhen

How Does an SCR Solenoid Valve Work?

The working principle of the SCR solenoid valve relies on the electromagnetic system. An electric current passing through a coil generates a magnetic field, which drives the movement of an internal valve plunger. This movement controls the opening or closing of the valve port, allowing the passage or stopping the flow of DEF.

In the SCR system, the engine control unit (ECU) sends signals to the solenoid valve based on the engine load and temperature, NOx concentration, and other factors. Then, the valve accurately injects DEF into the exhaust gas. Once injected, the DEF decomposes into ammonia, which reacts with the NOx gases in the catalyst and converts them to nitrogen and water. The whole process is optimized to reduce NOx emissions.

Automotive SCR Solenoid Valve Application

A SCR solenoid valve is used in various industries to control NOx emissions. They are critical components in diesel engine systems, such as passenger cars, trucks, and buses in the automotive industry, enabling DEF injection to meet emissions criteria. They are also used in heavy-duty SCR applications such as construction machinery, mining vehicles, and agricultural equipment in different operating conditions to reduce NOx emissions. They are also useful in the marine engine industry due to environmental regulations in the shipping industry.

In addition, they are used in industrial generators and power plants to reduce emissions produced by diesel engines used to generate energy. They are also used in stationary engine and backup power supply systems to comply with environmental requirements.

In summary, SCR solenoid valves play a critical role in reducing environmental pollution, enhancing air quality, and complying with international emission standards in various industries.

Advantages and Disadvantages of SCR Solenoid Valve

Advantages of SCR Solenoid Valve

Fix DEF Injection Control

The SCR solenoid valve ensures accurate and fast control of diesel exhaust fluid (DEF) injection to achieve optimal NOx reduction.

Substantial Emission Cuts

It is crucial for the reduction of NOx emissions to meet strict standards such as Euro VI and EPA regulations for diesel engines.

Fast Reaction Time

The electromagnetic actuation opens and closes the valves rapidly and adjusts depending on the load, temperature, and exhaust parameters.

Extreme Durability in Harsh Environments

These valves are durable and can withstand automotive and industrial applications exposed to high temperatures, vibrations, and DEF fluids.

Improved Fuel Economy

SCR systems with solenoid valves optimize combustion and emission processes to enhance engine efficiency compared to other emission control systems.

Compact and Easy to Integrate.

The SCR solenoid valves are compact and lightweight and thus easy to install in modern engine and exhaust systems.

Low Power Usage

They require low amounts of electrical power and are suitable for energy-efficient vehicle systems.

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❌ Solenoid Valve SCR Disadvantage

Sensitive to DEF Quality

Contaminated or poor DEF quality affects its performance and causes valve clogging or malfunction.

Maintenance Requirements

Regular inspection and cleaning are necessary to avoid deposits affecting valve operation in harsh conditions.

Complex System

The SCR systems that incorporate solenoid valves involve a complex design with integrated sensors, an ECU, and catalysts.

Higher Initial Cost

The initial capital invested in the SCR system, including the solenoid valves, is higher than basic emission control systems.

Crystallization Risk

DEF tends to crystallize during bad shutdowns or low temperatures, causing valve blockages.

Dependence on Electrical Control

The valve relies heavily on ECU signals and is thus prone to errors during electronic malfunctions.

Poor Performance in Extreme Conditions

Extreme heat or cold impacts DEF properties and valve responses if the design is inadequate.

Guide to Troubleshooting SCR Solenoid Valve

🔹 1. Possible Faults and Causes

❌Valve Won’t Activate

Reasons:

Problem with the power or wiring

Burnt-out coil

Not receiving the signal from the ECU

Plunger blockage due to deposits or crystallization

Solutions

Testing of wiring continuity and voltage supply

Measuring the resistance of the coil

Checking the out signal of the ECU

Replacing the valve if stuck

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❌ Improper DEF Dosing

Reasons:

Crystal buildup

Polluted or low-quality DEF fluid

Improper command signals

Worn out valve components

Solutions

Clean or flush the valve.

Replenish with new, high-quality DEF

Calibrating or checking ECU settings.

Replacing worn parts.

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❌ Def Leaks

Causes:

O-ring or seal degradation

Cracked valve housing

Fasteners not tightly fitting.

Solutions:

Replacing gaskets or seals

Tightening all connections.

Replacing valve body

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❌ Slow Response Time

Probable Causes:

Weak electromagnetic coil

Drop in voltage

Internal contamination

Solutions:

Ensure stable voltage supply

Cleaning up internal elements

Replacing an old or weak coil.

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❌ Buzzing or clicking sounds

Possible Causes:

Unstable power supply

Vibration or wear

Loose connection

Solutions:

Stabilizing the voltage

Safe mounting

Replating old parts.

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🔹 2. Diagnostics – Step-by-step Procedure

Step 1: Inspecting the unit

Checking for leaks, corrosion or other damages

Verifying wiring harnesses and connector integrity

Step 2: Testing the electrical elements

Resistor check on coil (comparing results with specification)

Testing the voltage supply and ECU signal

Step 3: Function testing

Opening valve and verifying its work

Listening for clicking noise (indicates motion)

Step 4: Checking the flow

Measuring the flow rate

Looking for obstructions

Step 5: System diagnostics using tools

Using diagnostic tools to detect error codes

Monitoring NOx sensor and DEF dosing rates

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🔹 3. Preventive Maintenance Tips

✅ Using high-quality ISO-certified DEF

✅ No DEF accumulation in the system for long periods of time

✅ Periodic flushing of the system

✅ Protecting from overheating and cold exposure

✅ Regular inspections and cleaning

4. Quick Troubleshooting Table

Problem	Likely Cause	Recommended Action
No valve movement	Power or coil failure	Check wiring and replace
Poor DEF dosing	Clogging or ECU issue	Clean / recalibrate
Leakage	Seal damage	Replace seals
Slow response	Low voltage / deposits	Clean / stabilize power
Noise	Loose or worn parts	Tighten / replace

🔹 5. Pro Tips (Experience in Field)

DEF crystallization accounts for 95% of cases; make sure to check for it first.

Connector damage by corrosion often causes electrical failure in harsh conditions.

Many “valve failures” aren’t valve problems but sensor or ECU calibration issues.

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🔹 Resume

Most likely sources of failure are electrical faults and DEF contamination or crystallization. Proper diagnostics and maintenance routines will quickly detect and solve any problem. Inspection, electrical, and flow tests.

Longevity and reliable emission performance require preventive maintenance.

FAQs of Automotive SCR Solenoid Valve

A1: The SCR solenoid valve controls the air flow during the regeneration phase.

Comment: The SCR solenoid valve or DEF doser valve is a sophisticated part controlled by the engine ECU. Its main purpose is dosing a precise amount of diesel exhaust fluid (DEF) to the exhaust. Upon evaporation the fluid splits into ammonia and converts the harmful nitrogen oxides into nitrogen and water vapor through the SCR catalyst.

Q2: I have a fault code SPN 4375 FMI 18. What does it mean?

Comment: Code SPN 4375 FMI 18 relates to “response fault.” It means that the engine computer (ECM) issued a command to either open or close the valve, and its response did not correspond to the order. The computer simply says, “I’ve ordered to inject such-and-such quantity of DEF, and you failed to respond.”

Q3: What are possible ways the SCR solenoid valve to fail?

Comment: First of all, it is crystallization of DEF. DEF is a liquid which upon drying turns into urea crystals. If the engine has been shut without purging the system, DEF would crystallize inside the valve tip and thus block it. Other possible reasons are wiring harness failures (wear and corrosion) and coil failures (open or short circuit).

Q4: How can I tell whether it's closed or opened?

Comment: Depending on the specific failure mode:

Stuck Closed (High Current/Low Flow) A short circuit or valve malfunction might trigger Code 1076-6 (Current Above Normal). This means that the ECU detected too much current but zero flow of fluid.

Stuck Open (Low Current/High Flow) If the circuit is broken or the valve won’t close, you will receive Code 1076-5 (Current Below Normal). The ECU fails to detect electrical resistance

No Response (FMI 18): Slow reaction of the valve (typically because of crystallization)

Q5: Can I simply clean the valve or should I replace it?

Comment: If the issue appeared recently, you might try cleaning it. Removing the valve and soaking it in warm water (no sharp instruments or compressed air, which could damage its delicate surfaces). But if there is an internal electrical problem (the coil has gone bad) or it has crystallized for a long time and worn its mechanisms out, replacement is unavoidable.

Q6: Can we continue driving with the SCR solenoid valve out of order?

Comment: Don’t turn around. The operation of the valve is crucial for the proper work of the SCR system. As long as the valve fails to respond the engine will derate. Initially it’s a warning sign, but later on the engine speeds down to almost zero (or even disables) in order to reduce the emission levels.

Q7: How can I check the valve and the wiring separately?

Comment: Using a multimeter and jumper wire

Testing the Wiring Disconnect the valve. Test resistance between the ECU/relay and harness pins. 5 Ohm resistance or less. -1. High resistance = Wiring problem

Testing the Valve/Circuit: Disconnect the valve. Short its harness connector pins. If the fault code has changed (for example, from “Open Circuit” to “Short Circuit”), then wiring is fine; otherwise, you have a valve problem

Q8: What makes this SCR solenoid valve prone to failure in winter and summer?

Comment: Oddly enough, but for different reasons.

Winter: DEF freezes at -11°C. In case the engine fails its warming-up or purging cycle, the frozen liquid will expand, damaging the seals or the valve body.

Summer: Due to the heat DEF dries up, leaving behind urea crystals which block the plunger

How To Choose SCR Solenoid Valve

When choosing an SCR solenoid valve

There are several technical and practical aspects to consider. First, the operational environment should be evaluated. Since SCR systems operate under high temperatures and harsh conditions, the solenoid valve must be highly durable. Stainless and high-grade plastics are commonly used in these valves.

Next,

Flow rate and pressure requirements should be evaluated. The solenoid valve must be capable of delivering the right dose of DEF in accordance with the engine requirements. Selecting a valve with the right flow rates will result in optimal performance in emission control.

Thirdly,

The response time is another aspect that must be evaluated. A solenoid valve with a rapid reaction time enhances injection accuracy. Thus, valves with high-speed switching capability and efficient electromagnetic designs should be selected.

Fourth,

Compatibility with the engine control unit (ECU) must be assessed. The valve must be capable of supporting the ECU control signals used in the system.

Fifth, the durability and lifecycle must be evaluated. High-quality SCR solenoid valves can withstand millions of cycles. As a result, the frequency of maintenance is minimized.

Furthermore, the installation area and design should be considered. The modern engine compartment space is limited, and thus compact valves are highly preferable.

Lastly, industry standards and certifications must be reviewed. Choosing valves that comply with automotive emission criteria assures performance and reliability.

Through careful evaluation of these considerations, engineers and buyers will be able to select the most suitable SCR solenoid valves.