If you have one of these units that's defective, you can check into the cost of replacing. Timer diagnosis If the timer drive motor is not advancing only in certain cycles, there may be a switch or thermostat that feeds it that is bad. If you need to, you can draw a picture of the terminal arrangement and wire colors. To test, unplug the machine and remove the two motor leads. Usually the terminals on the outside of the timer are stamped or printed with the color of the wire that is supposed to attach. So if the heater is burnt out, the detergent dispenser won't work. Solenoids should show some resistance, but continuity should be good. The easiest way is to go through everything else in the system that's malfunctioning. They all test. This includes not only the component that you suspect, but all switches leading to it, and sometimes other components, too. Each component should be labelled clearly on your diagram.
In addition to telling the motor when to run, it may also activate the heating circuit or heating control circuits, fill valve, detergent dispensers, motor direction or drain valve solenoid, etc. The symbols used to represent each component are pretty universal. These switches are located inside of the timer (you know this because they are drawn with thick lines.) They must be closed. Let's say you've got a detergent dispenser problem. Leave that to the design engineers. Please share our dishwasher electrical problems page. It controls everything in the cycle.