DEH P4901B in place of a JBL MR-4 in my boat

No user serviceable parts! If not working just replace!

if it has aux input rca's, then go to an electronics or car audio shop and buy a "stereo rca to 3.5mm headphone jack adapter cable" This will then plug into the headphone jack on the ipod.

I have the exact same issue. I have swapped with two identical MR17.2 radios and swapped out the sirius receiver. No change. I even bought a remote thinking I had to have a remote installed to get it to work...still no diff. Have you ever found a solution?

If a boat is anything like a car, the amp's negative post should not be connected to the battery, but to the ground of the boat. In a car, the entire chassis is grounded to the negative terminal, so when you run a line from the positive terminal of the battery to the positive post on the amp, and a line from the negative post on the amp to the chassis it is a complete circuit. I highly recommend placing a fuse on the positive line from the battery to the amp. Wiring this way prevents the amp from blowing up your battery, as well as prevents the battery from blowing your amp. Hope it works.

yes i am a repair shop and i have had nothing but problems out of those units you might want to look into a different unit boss marine is a good choice

have you ever cleaned the lazer lens? goto any CD store and pick up a CD cleaner CD, it is a CD that you place a drop of cleaner on the brushes on the bottom of place it in the CD player and let it play, it will clean the lens that reads the cd, you might have to run it a few times if you have never done this before. that should fix the problem. the CD cleaners are not that expansive, can find them under $20...... hope this helps you..........

The unit probably doesn't think there is a CD inside. Possible doing a soft reset will fix this. Do so by powering the unit and putting a ball point or other pointed object into the reset button opening either on the face of the radio or behind the face. A hard reset can be done by disconnecting constant power from the unit for approximately 15 seconds.
If either of these methods fail, then your unit has a bad CD mechanism or more than 1 CD inside the player. In that case, the unit will have to be serviced by an electronics repair or a local stereo shop. This is a Marine radio, and if installed on a boat, this problem is not too uncommon. Moist air can cause damage to the unit as well as the bouncing on the water that boats do.

i cant get sirius to work at all, there is a new tuner but jumps back to aux wish i would of bought something else

This link will take you to the Pioneer page with the link for both the Owner's Manual and the Installation manual of your specific model.

http://www.pioneerelectronics.com/PUSA/Products/CarAudioVideo/Source/CD-Players/DEH-P490IB?tab=D

Clicking on the link will ask you to register (no cost involved) and then you can download or view the manual.

Hope this helps