Measuring on A Throttle Valve Control Motor DC

Firstly, we need to make it clear that the measurement example is a DC motor and its signal type and signal level are respectively duty cycle varying, positive or negative; -12v to +12v. The throttle valve controls the operation of the motor

Workings of the throttle valve control motor DC

Many engine management systems include an idle control motor. In older versions, idle speed was controlled by an external valve that bypassed the throttle. Throttle valve, as an alternative to the external version, the throttle valve controlling the main throttle valve is increasingly used. It is possible that the throttle motor is used by a "drive by wire" system. Throttle control motors are not only used for idle speed regulation, but also for engines under (high) load. The two end of a DC motor are connected to the H-bridge of the ECU. Duty cycle and frequency variation of the H-bridge signal. On other cars, the signal might just be a duty cycle change.

The motor-controlled throttle is held in the neutral position by a spring. In this position, the engine runs at approximately 1000 to 1500 rpm. When the engine needs to run at a lower speed, the ECU applies a positive duty cycle signal to the motor, bringing the throttle to nearly closed. When the engine needs to go faster, a negative duty cycle signal is applied to open the throttle further. The polarity and duty cycle of the signal determine the direction and amount the throttle is opened from its neutral position. The ECU uses the signal from pressure sensor to determine the exact position of the throttle.

Measuring on a throttle valve control motor DC

Measuring signal voltage at positive and negative side of DC motor can check the correct function of the control motor. First of all, we need to connect the lab scope, which is connected to the throttle motor via the TP-C1812B measurement cable and the TP-BP85 rear probe. The lab scope has been set to normal scope mode with an infinite trigger delay. Use these settings when starting a single measurement, which is performed when the key is turned to the ON position. Start the measurement by turning the key to the on position. At the beginning of the measurement, the duty cycle signal is positive, followed by a short negative period. Subsequently, the signal remains positive and varies the duty cycle signal to maintain the throttle at a position that allows enough air to pass through that the engine will start.

A possible problem and cause with the following signals

The electronic throttle motor is an important part of the electronic control system. Therefore,  you should notice the following signals that may tell you there is a problem on it after measuring.

1. No signal: back probe is not connected (connection test), H bridge failure, throttle control motor failure.

2. Signal voltage is too high: the ECU is improperly grounded or ungrounded, and the ECU connection resistance.

3. A noisy signal: signal wiring is damaged, terminal contact is poor, throttle control motor fault.

4. Signal display offset: the range is not set to DC coupling.