The science behind the gizmos

Understanding the complexities of simple systems

Published:  02 April, 2015

By James Dillon

The advance in vehicle technology is undoubtedly very fast, driven by legislation and the desire by the vehicle manufacturer to offer the latest features and operational trinkets to win the new car sale. Many of the cool features car buyers have come to expect as standard have technology at their heart. Consequently, many of the control processes and techniques which live under the surface of the modern vehicle are responsible for these cool in-car features. Even functions as mundane as the operation of the lights, wipers, locks and windows now involve some very clever tech.

Figure 1

Part of the clue is in the detail of the diagram concerning the switch. Take a close look and you'll see that the output side of the switch is connected directly to ground (pin 34).

Figure 2

In the old days of relays and switches, a multimeter could be used to diagnose many faults. However, as modern circuits like this show, a signal at 100Hz is too fast to be accurately displayed by a multimeter, which typically samples much more slowly than this.

The second part of the waveform, see Figure 2, shows the switch in the turn left position for just over a second. During the switch operation, the signal is pulled down directly to ground. During this time the body control module interprets this as a sign to turn on the left hand indicator bulbs. The waveform returns to full height as soon as the switch is returned to the rest position.

The next part of the puzzle is to determine how the body control unit operates the one touch, triple flash. The clue here is that function of the indicator stalk (providing a ground, either resistive or direct) is the same for both the one touch and standard operation. Therefore, the body control unit uses an internal timer to measure the grounding event. If the signal is altered (either pulled down directly or through the resistor) for up to 600 milliseconds, the indicators are operated in triple flash mode. If the signal is detected for greater than 600 milliseconds, they are operated full time, until the input signal returns to the off position.

Additionally, the body control module has several other inputs which will trigger the indicator function. These inputs are from the hazard light switch and the remote central locking control unit. The hazard light switch operates in the same way as the indicator stalk (grounding a signal), however, the central locking sends a 'flash the indicators' via the vehicle network (CAN in this case). The final part of this simple complex system is the way in which the instrument indicator notification lamps work. In traditional systems there would have been a direct wire; a bulb and a ground for each side but, in newer systems, the instruction to bring the notification lamps on in the instrument cluster is carried between the body control unit and the instrument panel via the CAN Bus.

It's interesting to see how the newer style technology works and even more interesting is to consider how this will affect the way that diagnostics and troubleshooting should be carried out. I wonder how the garages that don't invest in education, information and equipment are going to manage in the future. Probably by using a liberal smattering of 'parts darts'! All very interesting until you consider that some of these parts are one time use and will require coding or programming to the vehicle.



Find out more about James Dillon's training please call Technical Topics on 01278 428 699.

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