Under the dash, and over my head

Automobile companies employ sadists to decide where to place a vehicle's radio.

By Brad Thompson, Contributing Technical Editor -- Test & Measurement World, 8/1/2010 12:00:00 AM

Our 2004 Nissan Quest minivan's CD changer ate a disc, and a local garage estimated that repairs would cost several hundred dollars. I figured that I could pull the radio and connect a power supply, an antenna, and a couple of loudspeakers to verify the repairs. While it was on the bench, I'd add audio inputs to accommodate a Sirius satellite receiver I'd received as a gift.


I extracted the radio assembly, a featureless metal box that sports no controls-those are embedded in the "coffee table." The CD drive looks nothing like a consumer-audio product, and its broken plastic innards told me that it was beyond repair. As for adding audio inputs, I downloaded the radio's schematic and was stymied. Without knowledge of its internal architecture and data-bus protocols, I couldn't figure out where to attach external audio.

Even armed with my HP 16500B logic analyzer and lots of spare time, attempting to reverse-engineer the various buses' signals would require a test-bench fixture. Short of stripping wiring harnesses and controls from a wrecked Quest, where could I find mates for those unfamiliar-looking connectors selected by Nissan's practical jokers? In short, I was in over my head.

Defeated, I ordered a replacement CD drive ($45) and an after-market adapter pod ($90) that plugs into the radio's unused mystery connectors and provides audio inputs for the Sirius receiver. I now have a fully functioning installation and an appreciation for the degree to which a once easily diagnosed and tested box-with-knobs "radio" has mutated into a vehicle-integrated, microprocessor-intensive, bus-oriented "entertainment system."

Now, wasn't that fun?

READ THIS FIRST! Always disconnect a vehicle's battery ground strap before venturing under the dash. Never attempt to remove the positive (hot) terminal connector, as a slip of the wrench can cause a massive short circuit and battery explosion. Disconnecting the ground strap also disables the vehicle's airbag system, preventing accidental actuation. DIY repair tips Repairing a modern automobile's entertainment system far exceeds the capabilities of most of us. But if you decide to go ahead, here are a few suggestions: • Begin by reviewing the owner's manual to verify your understanding of how the entertainment system should work. • Reread the warranty statement. If you're lucky, warranty coverage will pay for repairs. Your attempted repairs will likely void any remaining warranty. • Check the vehicle's fuse panel for blown fuses. Vaporized metal in a fuse implies a massive overload. • Ask yourself "What's changed?" Could seemingly unrelated repairs have affected the entertainment system? • Search the Internet for similar problems reported by other owners. • Obtain the documentation. Specifically, get removal and replacement instructions and a repair manual (if available). • Survey your toolkit. You'll need more than a screwdriver and an adjustable wrench to remove most entertainment systems. • Make a test plan. What instruments are needed to verify your repairs? Resources There's a paucity of general information regarding radio removal and repairs. Your best bet is to use a specific vehicle's manufacturer, model, and year as search terms. Some listings may appear under "radio" or "audio system." This Website offers some basic advice: www.fixitclub.com/Electronics/Car_Radio.shtml?page=1