Analysis Report on the Necessity of Automotive ECU Electromagnetic Compatibility Testing

1. Introduction

Definition of Electromagnetic Compatibility (EMC) and Its Relevance to Automotive ECUs

The core essence of Electromagnetic Compatibility (EMC) embodies a dual attribute of "interference and immunity," meaning that electronic equipment or systems can operate normally in their electromagnetic environment without causing unacceptable electromagnetic interference to other devices in that environment. This attribute manifests in two aspects: on one hand, the equipment needs the ability to resist external electromagnetic interference (Electromagnetic Susceptibility, EMS); on the other hand, the equipment itself should not generate electromagnetic interference exceeding standards (Electromagnetic Interference, EMI).

Addressing this characteristic, the industry commonly adopts a "combination of suppression and diversion" design philosophy to handle electromagnetic issues: for conducted interference, diversion is achieved through components like capacitors, TVS diodes, etc., or blocking via ferrite beads, resistors, and common-mode inductors; for radiated interference, a balance between diversion and blocking is achieved through shielding measures.

With the rapid development of automotive electrification and intelligence, the complexity of vehicle electronic systems has significantly increased, and the number of electronic components has surged dramatically. Modern vehicles are equipped with an average of over 50 Electronic Control Units (ECUs). As the "brain" of the automotive electronic system, ECUs encompass key components such as the Engine Control Module and Body Control Module, operating in an environment filled with various electromagnetic interference sources like radiation, conduction, and Electrostatic Discharge (ESD).

The dense layout of numerous ECUs leads to a sharp increase in electromagnetic coupling risks. For example, when the power cable of a modified amplifier is close to an ECU, it may cause Electromagnetic Frequency Interference (EMFI), leading to failure of the knock sensor system and resulting in vehicle power loss. Furthermore, EMC issues can also cause GPS failure, radio static, and even affect the safety of autonomous driving systems.

In this context, EMC testing has become a critical means to ensure the performance stability of automotive ECUs. The electromagnetic compatibility of automotive ECUs is directly related to the vehicle's safety, reliability, and functional stability. For instance, ECU failure can lead to issues like no NE signal and starting difficulties. International standards such as CISPR 25 specifically address the electromagnetic compatibility requirements for automotive components, clearly stipulating that vehicle electronic devices must maintain normal operation capability in specific electromagnetic environments, providing unified specifications for ECU EMC testing.

Report Scope and Objectives

With the rapid development of automotive electronic technology, the in-vehicle electromagnetic environment exhibits significant complexity. The vehicle interior contains numerous transient interferences generated by inductive loads (such as motors, relays, etc.) during switching operations. Simultaneously, the superposition of multi-frequency band signals formed by the operation of multiple electronic devices (such as automotive radar, communication modules, entertainment systems, etc.) makes EMC issues increasingly prominent.

The research scope of this report mainly includes three dimensions: first, the electromagnetic compatibility standard system, sorting out the domestic and international standard frameworks applicable to automotive scenarios; second, testing methods and scenario boundary conditions, clarifying EMC verification requirements for different vehicle types (traditional fuel vehicles and new energy vehicles) and different levels (vehicle level and component level); third, the logic for selecting key testing equipment, analyzing the core composition and technical requirements of testing systems.

Through the above research, the aim is to provide scientific and systematic electromagnetic compatibility solutions for relevant enterprises and institutions, ultimately achieving the goals of reducing product compliance costs and avoiding safety risks caused by electromagnetic interference.

2. Analysis of the Necessity of Automotive ECU Electromagnetic Compatibility Testing

Regulatory and Market Access Requirements

Electromagnetic compatibility testing for automotive ECUs is a mandatory threshold for products to enter domestic and international markets, and their compliance directly depends on meeting the regulatory systems of different regions. At the international level, the European Union has established an EMC access framework for vehicles and electronic components through UN ECE R10 regulations (E-mark certification), requiring all Electronic Sub-Assemblies (ESAs) to pass multiple tests including Radiated Emission (30MHz-1GHz), Radiated Immunity (20-400MHz, 400MHz-2GHz), Transient Immunity (ISO 7637-2), etc., and must comply with international standards such as CISPR 25 and ISO 11452.

In the domestic market, the CCC certification system is the core. GB/T 18655-2025, as the mandatory requirement after the standard revision in 2025, replaces GB/T 18655-2018, adopts CISPR 25:2021 equivalently, and clearly specifies the limits and measurement methods for radio disturbance characteristics of vehicles and electronic components. According to the "Implementation Rules for the Revision of Technical Standards for Road Transport Vehicle Models (Trial)", starting from 2025, all new vehicle model declarations must submit test reports compliant with GB/T 18655-2025. ECU products that fail the tests will be prohibited from being installed in vehicles.

EU E-mark Certification Requirements

Radiated Emission Test (30MHz-1GHz)
Radiated Immunity Test (20-400MHz, 400MHz-2GHz)
Transient Immunity Test (ISO 7637-2)
Compliance with CISPR 25, ISO 11452, etc.

Domestic CCC Certification Requirements

GB/T 18655-2025 Standard Revision
Equivalent Adoption of CISPR 25:2021
Mandatory Implementation from 2025
Prohibition of Installation if Tests are Failed

Functional Safety and Failure Risks

The Electromagnetic Compatibility (EMC) performance of automotive ECUs is directly related to vehicle functional safety. Electromagnetic interference can severely impact vehicle safety and economy through the "failure mode - consequence - cost" chain. ECU failure modes caused by electromagnetic interference are diverse, including excessive conducted emission, radiated immunity failure, electrostatic discharge failure, etc.

Test Item	Frequency Point	Measured Value (dBuV)	Limit (dBuV)	Exceedance (dBuV)	Potential Impact
Positive Conducted Emission	6.12MHz	60.644	45	15.644	Interference with other vehicle devices
Negative Conducted Emission	5.96MHz	57.326	45	12.326	Interference with other vehicle devices

Technology Development Drivers

The deep development of intelligentization, electrification, and connectivity in the automotive industry is fundamentally changing the electromagnetic environment of vehicle electronic systems, imposing higher requirements on Electromagnetic Compatibility (EMC) testing. With the integration of key components such as processors, sensors, and communication equipment in intelligent driving systems, and the proliferation of high-voltage power systems and charging facilities in new energy vehicles, the number and complexity of vehicle electronic devices have significantly increased. The types of electromagnetic interference sources have multiplied, interference intensity has increased, and the electromagnetic environment has become increasingly complex.

New Semiconductor Technologies

Wide-bandgap devices represented by Silicon Carbide (SiC), with their high switching speed characteristics, improve power system efficiency, but their steep switching edges generate significant high-frequency spurious emissions, challenging traditional test frequency band coverage.

Communication Technology Upgrades

The application of 5G-V2X communication technology extends the operating frequency band to 5.9GHz (covering DSRC bands). The CISPR 25 Ed.5.0 standard has expanded the frequency test range to 5.925GHz to accommodate this demand.

3. Domestic and International Electromagnetic Compatibility Testing Standards

Domestic Standard System

Basic General Standards

In the domestic basic general standard system for vehicle electromagnetic compatibility, GB/T 18655-2025 (replacing GB/T 18655-2018) is one of the core standards. Its full title is "Vehicles, boats and internal combustion engines - Radio disturbance characteristics - Limits and methods of measurement for the protection of on-board receivers". It equivalently adopts the international standard CISPR 25:2021, specifies the limits and measurement methods for radio disturbance characteristics in the frequency range of 150 kHz to 5925 MHz, and is applicable to protect on-board receivers from electromagnetic disturbances generated by electrical/electronic components or modules in the same vehicle.

This standard underwent important updates in the 2025 version, mainly reflected in the following aspects: First, it added electromagnetic disturbance limit requirements for the Beidou navigation system operating frequency band (1553-1569 MHz) to adapt to the popularization of vehicle Beidou navigation equipment and electromagnetic environment protection needs; Second, it deleted the TEM cell test method used in the original standard, unified the use of ALSE (Antenna Method) as the primary measurement method, optimized the testing process, and improved the consistency of measurement results.

Industry and Enterprise Standards

In the domestic electromagnetic compatibility testing standard system, industry and enterprise standards usually serve as supplements and extensions to national standards, and often have stricter technical requirements to meet the higher EMC demands of vehicle manufacturers. Although domestic automotive enterprise standards like the GB/T 28046 series correspond to the international standard ISO 16750 as basic general requirements, leading vehicle manufacturers, based on their own quality control objectives, generally establish enterprise standards that are higher than national and industry standards.

Vehicle Manufacturer	Enterprise Standard	Corresponding International Standard	Test Items/Remarks
Volkswagen	TL965, TL82066 series standards	CISPR25, ISO7637, etc.	Interference test technical requirements and test methods
Ford	ES-XW7T-1A278-AC	RCB 200 series	Electromagnetic Emission Test
Ford	FMC 1278, EMC-CS-2009.1	RCB200N1	Electromagnetic Emission Test
Domestic Vehicle Manufacturers	GB/T 28046	ISO 16750	Basic General Requirements

International Standard System

CISPR and ISO Standards

CISPR and ISO standards form complementary positions in automotive ECU electromagnetic compatibility testing, jointly building a comprehensive testing framework covering Electromagnetic Interference (EMI) and Electromagnetic Susceptibility (EMS). Among them, the CISPR 25 standard focuses on EMI emission control, while the ISO standard system (centered on the ISO 11452 series) focuses on EMS immunity assessment.

CISPR 25: Core Standard for EMI Emission Control

CISPR 25 is developed by the International Special Committee on Radio Interference (CISPR), belonging to the IEC standard system. Its core goal is to limit the radio disturbance emissions of vehicle electronic/electrical components to protect on-board receivers (such as broadcast, GPS, Wi-Fi, V2X, etc.) from interference by devices in the same vehicle.

ISO Standards: Systematic Specifications for EMS Immunity Assessment

The ISO standard system focuses on immunity (EMS) testing, covering different interference types and test scenarios through multiple series of standards, among which the ISO 11452 series is the main basis for automotive electronic electromagnetic immunity testing.

SAE and UNECE Standards

In the regional standard system for automotive ECU Electromagnetic Compatibility (EMC) testing, SAE (Society of Automotive Engineers) and UNECE (United Nations Economic Commission for Europe) standards show significant differences, dominating the compliance requirements in the North American and European markets respectively, providing clear regionalized compliance paths for export-oriented ECU products.

SAE Standard System

SAE J2521: Dedicated EMC test specification for Electronic Control Units (ECUs)
SAE J551-3: Focuses on conducted emission
SAE J551-6: Targets radiated emission testing from 30 MHz to 1 GHz

UNECE Standards

UNECE R10 Regulation: Basis for EMC certification of EU vehicles and Electronic Sub-Assemblies (ESAs)
Revision 6 added EMC test requirements under "REESS charging mode"
Revision 7 (draft) proposes to extend radiated immunity test frequency to 6 GHz

4. Core Test Items for Automotive ECU Electromagnetic Compatibility

Electromagnetic Interference (EMI) Testing

Conducted Emission (CE)

Conducted Emission (CE) testing aims to detect the level of interference signals conducted through power lines or signal lines by automotive ECUs and other components, ensuring their frequency domain characteristics comply with relevant standard limits. It is one of the core items for assessing ECU electromagnetic compatibility.

Test Standards and Methods

Conducted emission testing is mainly conducted according to international and domestic standards, including CISPR 25, GB/T 18655, EN 50498, etc. Among them, CISPR 25 specifies two core test methods: Voltage Probe Method (CE-V) and Current Probe Method (CE-C).

Interference Source Localization and Propagation Path Analysis

The key to conducted emission testing lies in accurately identifying the interference source and propagation path, which directly affects the effectiveness of corrective measures. Taking an ECU rectification case as an example, testing found that it exceeded the limit by 15 dBμV in the 6 MHz frequency band. Further localization showed the interference source was the 20 kHz PWM switching noise of the H-bridge circuit.

Radiated Emission (RE)

Radiated Emission (RE) testing aims to evaluate the intensity of electromagnetic waves radiated into space by automotive ECUs and other components during operation, preventing them from interfering with vehicle communication systems (such as GPS, 5G, Wi-Fi, etc.) and other sensitive electronic devices. Testing is required to ensure radiation levels comply with international and domestic standard limits.

Test Method	Frequency Band Coverage	Cost Characteristics	Applicable Stage	Main Disadvantages
ALSE Method	150kHz~6GHz	High (Site construction and maintenance)	Final Certification Test	Strict environmental requirements
TEM Cell Method	9kHz~200MHz	Low	R&D Pre-test	Limited frequency band coverage
OATS Method	30MHz~1GHz	Medium	Alternative Option	Susceptible to external electromagnetic interference

Electromagnetic Susceptibility (EMS) Testing

Radiated Susceptibility (RS)

Radiated Susceptibility (RS) testing aims to evaluate the stable operating capability of automotive ECUs under external electromagnetic field interference, which is a key link in ensuring the reliability of vehicle electronic systems. This test needs to simulate interference sources in the real electromagnetic environment (such as 5G base stations, automotive radar, broadcast signals, etc.), verify the ECU's immunity to radiated electromagnetic fields through standardized methods, and quantify its performance combined with Performance Status Classification (FPSC Level I-IV).

Test Standards

Test standards are mainly based on the ISO 11452 series, with ISO 11452-2 as the core method. It specifies the use of an anechoic chamber (ALSE) environment, emitting electromagnetic fields of specific intensity through an antenna, covering the frequency range of 80MHz to 6GHz. The field strength is typically 30V/m (basic scenario), and needs to be increased to 600V/m for special scenarios like radar frequency bands.

Test Implementation

During test implementation, an electromagnetic environment needs to be constructed using a signal generator, power amplifier, and transmitting antenna. The antenna is aimed at the center of the DUT cable (80MHz~1GHz) or directly at the DUT (1GHz~6GHz) depending on the frequency band, applying an electromagnetic field at a distance of 1 meter, while simultaneously monitoring the working status of the ECU.

Bulk Current Injection (BCI)

The Bulk Current Injection (BCI) method is mainly used to evaluate the tolerance of automotive ECUs to electromagnetic interference conducted via wiring harnesses. Its core standard is ISO 11452-4, with a test frequency range covering 100 kHz to 400 MHz.

Test Principle

This test injects interference signals into the wiring harness of the ECU under test through a current injection probe (current transformer), simulating the scenario where interference currents induced by external RF fields on conductors enter the system through cable coupling, to verify the functional stability of the ECU in an interference environment.

Harness Coupling

Harness coupling is the main path for conducted interference because vehicle wiring harnesses are widely distributed and relatively long, easily becoming effective receiving antennas for external electromagnetic energy. Common-mode or differential-mode currents induced in the harness by external RF fields can directly act on the internal circuits of the ECU through conduction, potentially causing signal distortion, logic errors, or hardware damage.

Electrostatic Discharge (ESD) and Other Immunity Tests

Electrostatic Discharge (ESD) testing aims to simulate the electrostatic shock effect generated when a human body or object contacts the vehicle, ensuring the tolerance of automotive ECUs to electrostatic interference in actual use environments. This test is mainly based on the international standard ISO 10605 and the domestic equivalent standard GB/T 19951-2005 (quasi-equivalent to ISO 10605:2001), while also referring to the resistance-capacitance module configuration in the IEC 61000-4-2 standard (e.g., R=330Ω/2000Ω, C=150pF/330pF) to distinguish electrostatic discharge conditions for different scenarios such as inside and outside the vehicle.

5. Automotive ECU Electromagnetic Compatibility Testing Equipment

EMI Testing Equipment

Core Measurement Instruments

In automotive ECU electromagnetic compatibility testing, the selection of core measurement instruments must strictly follow testing standards and technical requirements to ensure data accuracy and reliability. Among them, the EMI receiver, as a key equipment, must meet several technical indicators: First, it must comply with the CISPR 16-1-1 standard requirements for detectors, supporting quasi-peak, peak, and average detection to adapt to the measurement needs of electromagnetic interference signals in different frequency bands; Second, the frequency coverage must meet the testing standards, covering the measurement of interference signals from low frequency to high frequency for automotive ECUs.

EMI Receiver

Complies with CISPR 16-1-1 standard
Supports quasi-peak and average detection
Frequency range meets standard test requirements

Line Impedance Stabilization Network (LISN)

Isolates grid noise
Stabilizes line impedance (typically 50Ω)
Used for conducted emission testing

Antenna and Anechoic Chamber System

In automotive ECU electromagnetic compatibility testing, the antenna and anechoic chamber system are core components to ensure the accuracy of Radiated Emission (RE) testing. For different frequency band testing needs, appropriate antenna types must be selected: Biconical antenna is suitable for medium and low frequency bands, covering 30MHz~300MHz; Log-periodic antenna (200MHz-1GHz) and Horn antenna (1GHz-6GHz) are suitable for medium and high frequency bands, with Horn antenna performing better in high frequency bands (typically above 1GHz).

Specification Item	CISPR 25 Standard Requirement	ISO 11452-2 Standard Requirement
DUT-Antenna Distance	1m	1m
Antenna-Absorber Material Distance	≥1m	≥0.5m
Antenna-Ground Distance	≥0.25m	≥0.25m

EMS Testing Equipment

Signal Generation and Power Amplification System

The signal generation and power amplification system is the core equipment combination for achieving radiated immunity and transient immunity testing in automotive ECU electromagnetic compatibility testing. Its collaborative working capability directly determines the accuracy and reliability of the tests. This system mainly consists of a signal generator and a power amplifier, which must achieve precise matching in bandwidth, power, and control logic to meet standard test requirements.

Signal Generator

Frequency coverage 9 kHz to 6 GHz
Supports AM/FM/PM modulation

Power Amplifier

Operating frequency 10 kHz~6 GHz
Output power up to 150W

Injection and Coupling Devices

Injection and coupling devices are key components in automotive ECU electromagnetic compatibility EMS testing for precisely injecting or coupling interference signals into the system under test. Their application scenarios vary in targeting due to differences in principles and structures, and corresponding equipment solutions need to be configured according to test item requirements.

Test Item	Required Equipment	Key Components/Parameters
BCI Test	Current Injection Probe System	Current Injection Probe (0.1-400MHz) Calibration Fixture
Compact Space Radiated Immunity Test	TEM Cell	DC-500MHz Operating Frequency

6. Standard Updates and Technology Trends

Key Changes in CISPR 25 Ed.5.0

CISPR 25 Ed.5.0 (released in December 2021), as an important update replacing the 2016 version, introduces several key changes in test frequency range, test methods, and technical requirements, significantly impacting the electromagnetic compatibility testing of automotive ECUs.

Frequency Range Extension and Communication Band Coverage

This version extends the test frequency range from the original 150kHz~2500MHz to 150kHz~5925MHz. The newly added 5.925GHz band directly covers 5G-V2X communication applications (such as the 5.9GHz DSRC band). This adjustment aims to adapt to the development needs of vehicle wireless communication technology.

Optimization of Test Methods and Environmental Requirements

The new version deletes the original Transverse Electromagnetic (TEM) cell test method appendix, instead emphasizing more precise electromagnetic shielded room test environments, and imposes stricter requirements on the performance of the shielded room to ensure the accuracy and repeatability of high-frequency band test results.

Change Category	Specific Change Content	Impact Scope
Test Environment	Deleted TEM cell test method; Strengthened electromagnetic shielded room requirements	Improved high-frequency band test accuracy
Measurement Standards	Added uncertainty assessment guidelines (Appendix J-M)	Enhanced test data credibility
Conducted Emission	Tightened limits for FM band (76MHz～108MHz)	Optimization of filter circuits and grounding design

New Energy Vehicle EMC Testing Challenges

The intelligentization, electrification development, and application of emerging technologies in new energy vehicles pose multi-dimensional challenges to Electromagnetic Compatibility (EMC) testing, which need to be systematically addressed through a "layered testing" strategy. Current challenges mainly stem from increased system complexity, increased electromagnetic interference sources, deterioration of the electromagnetic environment, and upgrades in regulations and standards.

Intelligentization and Integration

Under the trend of intelligentization and integration, the application of domain controllers and zonal controllers significantly increases system complexity, while the multiple sensors integrated in ADAS and intelligent driving systems (such as 77GHz millimeter-wave radar, 1550nm LiDAR) further exacerbate electromagnetic interference risks.

Electrification

Electrification brings high-voltage systems (e.g., 1500V batteries) and power systems (motor controllers, DC-DC converters). Due to large current jumps in short times and rapid switching actions of high-power semiconductors, they generate intense wideband radiation (30MHz-1GHz) and conducted interference, making EMC issues more prominent.

Test Subsystem	Core Test Objects	Key Test Requirements	Specialized Equipment and Technology
High-Voltage System and High-Voltage Harness	High-Voltage Harness/Motor Controller/DC-DC Converter	Shielding Effectiveness SE≥60dB 10kHz-30MHz Conducted Interference Assessment 100V/μs Transient Interference Test	Shielding Effectiveness Test System Conducted Immunity Test System Transient Immunity Test System
ADAS and Intelligent Driving System	ADAS ECU/Multi-sensor Coordination	Out-of-band Radiation Suppression Functional Safety Verification in Complex Electromagnetic Environment	Scenario Simulator Synchronous Triggering Interference Waveform Injection Technology

7. Conclusions and Recommendations

Core Conclusions

The core value of automotive ECU electromagnetic compatibility testing lies in practicing the concept of "testing upfront," that is, identifying and resolving potential electromagnetic compatibility issues early in the R&D stage through scientific and standardized pre-testing, thereby significantly reducing subsequent rectification costs and improving product reliability.

Analyzing from the economic cost dimension, the cost of rectifying EMC issues during the R&D stage is approximately 50,000 to 100,000 RMB, whereas if problems are exposed in the after-sales stage, the rectification cost can reach 10 million RMB. For mass-produced vehicle models, the cumulative losses will grow exponentially. This cost difference highlights the necessity of moving the EMC testing phase forward to the R&D stage. By identifying electromagnetic risks and optimizing designs early in the product development phase, high investments due to late-stage rectifications can be effectively avoided, while ensuring functional safety and compliance throughout the vehicle's lifecycle.

Engineering Practice Recommendations

To systematically improve the Electromagnetic Compatibility (EMC) performance of automotive ECUs, it is necessary to build a closed-loop optimization system of "standards - testing - rectification." Through full-process management including prevention in the design stage, localization in the testing stage, and optimization in the rectification stage, the synergistic improvement of EMC performance and product competitiveness can be achieved.

Design Stage

Optimize circuit board design
Adopt filter design
Local shielding for sensitive circuits
Introduce electromagnetic simulation tools

Testing Stage

Strictly follow international and domestic standards
Configure test environments and equipment hierarchically
Improve efficiency through automated test systems

Rectification Stage

Adopt a "combination of suppression and diversion" strategy
Optimize PCB layout or use metal shielding enclosures
Strengthen power supply filtering
Improve enclosure grounding and interface protection