Transistor Drivers
Transistor Drivers activate the components that perform the task for the CPU by, for example, grounding a relay coil or an interior lighting bulb.
The power amplifier transistors are power grounded, often through an extra thick pin in the connector. The lead, often 1-2.5 mm2 then goes to the body and is grounded separately from the signal ground, which feeds other internal components of the control module.
If there are great loads, such as from the radiator fan, ventilation fan, fuel pump or glow plug, additional power amplifiers or relays may be used.
The illustration above includes a pull-down. It has a high number of ohms and cannot ground the lead when the component is connected. The purpose of the resistor is simply to keep the pin pulled to ground in the event of a break so that diagnostics can find the fault.
A transistor driver can also be connected in the control module in such a way that it puts out B+. This has been used previously for direction indicators (ICE/DICE) and is now used for exterior lighting in UEC and REC.
In fault tracing, one is often instructed to test an output with an LED. For normal outputs that ground, it is connected between B+ and the control module output. When you then activate it with the diagnostic tool, the LED should light. This shows that the lead is whole.