That means that something has gone wrong, and you have blown fuses inside the head unit.
Here is a post from a Pioneer employee on one of their forums to help explain.




In an effort to limit damage done by ground loops and voltage racing to the deck from the amps via the RCAs, years ago Pioneer added small fuses to the circuit board. These fuses when blown, can cause the stereo to produce engine noise, but don't blame it on Pioneer just yet.

For one there is a reason that Voltage is traveling from the Amp to the deck via the RCAs, and you must figure this out or you will continue to have problems with any deck.

First you need to test to see if the fuses are blown. To do this simply use a DMM and check for continuity by touching the chassis of the deck and the outside shield of the RCA. If you have continuity, then the Fuses are fine and your engine noise lies elsewhere in the system. If you do not get continuity, then one or more of the fuses are most likely blown and you need to send the deck to a authorized service center for replacement.

If the fuse is blown then you need to find and fix the reason for the blown fuse before you reinstall the deck.
Common issues include: A loose or corroded ground from the amp. Make sure the ground is on bare metal and tightly fastened. A Loose or pinched RCAs. Make sure that the RCAs fit tight to the amp. I'm sure we all know that "POP" that comes from plugging in an RCA to a live system. This "POP" is enough to blow the fuse, so make sure that during the install the battery stays disconnected and if for any reason you need to unplug or move an RCA, power down the system, disconnect the battery and then make the adjustment. I know this extra 5 minutes can be a pain in the butt, but 5 minutes is better then up to two weeks at a repair facility.

Lastly, do not try to replace the fuses yourself. They are very small about the size of the tip of a ball point pen and require soldering. Only a local Pioneer Authorized service center or Pioneer Service should do the repair. In most cases that I have dealt with the service center by me can turn the deck around in 1-2 days.