Yes, it is true but it really does not help all that much.
Turn the car off and hold down the trip meter/odometer button thingy.
Now turn the key to the on position and start the car still holding down teh button, DO NOT LET IT GO YET. You will see your gauges go all the way to the right then back again, you can let go now and see that on board diagnostic.
You will see things like rpm, fuel pressure, stored dtc.