How to shorten ECU test time and improve test efficiency through various functions

Improper regulation of the automotive electrical system results in frequent voltage sags and overshoots. Under normal conditions, the voltage ranges from 11 to 15 volts, while during transient initiation and execution, it ranges from 8 to 24 volts. Therefore, voltage margin testing is required when testing engine control units (ECUs) to verify normal operation and tolerance under extreme bias voltage conditions.

In the highly competitive automotive electronics market, test time is of the essence. Testing at multiple bias voltage levels is a necessary but time-consuming operation in ECU testing. Most system DC power supplies take a long time to change to new output settings and stabilize, which increases the total test time. This article uses Agilent Technologies' N6700 modular power system and N6752A power supply module as examples to illustrate various functions that can shorten ECU test time and improve test performance.

ECU input and output characteristics

ECU uses many signals to monitor the vehicle and its environment, and then manage and control the engine and auxiliary equipment to achieve optimal operation. Figure 1 summarizes the many input and output signals of a typical ECU.


Figure 1: Many input and output signals of a typical ECU

In functional testing of an ECU, the right test system resources will simulate the various input signals in a controlled manner, and the outputs will be loaded and checked for the correct response. Given the number of inputs and outputs, it is clear that ECU testing requires a large amount of test system resources.

Critical Bias Voltage Levels in Automotive Power Systems

Depending on the operating state of the vehicle, certain voltage levels are often encountered in the automotive power system. These levels become critical voltages for ECU testing, as shown in Figure 2. Some of the relevant tests performed at these critical voltages include:

• Checking continuity between multiple ground, power, and high current driver pins when the power supply is set to 0 or off.

• Applying a very low voltage and measuring the resulting current to check for shorts or other unexpected errors.

• Various functional tests start at a low level of about 8 volts (representing a start) and go all the way up to a high level of about 15 volts (representing a fully charged condition).

• If an ECU voltage monitoring circuit is included, it is usually verified or validated using at least two terminal operating voltages.

• Verify the ECU low voltage reset level by checking the minimum “must not trip” and maximum “must trip” thresholds.

During testing, the ECU may experience up to 20 changes in bias voltage levels.


Figure 2: Certain voltage levels in the vehicle’s electrical system become important voltages for ECU testing

Power Supply Output Response Time

When changing the output voltage setting of a power supply to a new value, it must go through several steps, as shown in Figure 3. These steps take a limited amount of time. When the power supply receives a command, it must process it, so there is a command processing time. The power supply output then responds and changes to the new setting. The time it takes to reach the final value within a certain stable range is the output response time. A stable range of 1% is suitable for ECU testing. Special attention should be paid to the output response time when adjusting the setting down. Many power supplies must rely on a real DUT load to reduce the voltage. Under light load conditions, some power supplies without a set-down device may take a second or so to reach the final value. The N6752A power supply module has a built-in down-setting device that can speed up down-setting regardless of load. In ECU testing, both up-setting and down-setting must be fast. Speed

​​up testing with Agilent Technologies' N6700 Modular Power System and N6752A power supply module The test time saved by switching from a slower power supply to the N6700 and N6752A is the result of the shortened command processing and output response time multiplied by the number of output voltage transitions. Multiplying the 200 millisecond reduction by 15 output transitions gives a total test time reduction of 3 seconds. For an ECU test that takes up to 20 seconds, this is a 15% improvement in test speed. ECU manufacturers value this result because it helps reduce test costs and provides direct benefits.

Related Applications

• Automotive Electronic Control Module (ECM)

• Automotive Body Electronics System

• Automotive Telematics


Figure 3. Power Supply Command Processing and Output Response