I went to replace the radio in my 2004 Ford product, after the CD player failed. I was quite surprised-- and puzzled-- to find a whole bunch of wiring going to the radio that had little to do with the function of the radio. I did eventiually figure out which wiring was the radio, and the installation worked just fine.
I later found out that the radio's display was used as part of the OBD2 system, as a diagnostic display. So now, I have great tunes, but no diagnostics. I thought tis was a poor place to do this, as aftermarket car audio is a very popular thing. It soulds like this kind of thing is becoming more common, which means in the future, I am stuck with whatever the vehicle manufacturer installs for a radio.
One other thing I noticed is that Ford used an antenna connector unlike anything I had ever seen before. I had to make a pigtail adapter to allow the installation to be completed. I probably now have one of the very few cars anywhere with BNC connectors in the radio antenna line!
I once bought a used Plymouth Breeze. This car had a lot of problems: I had to have the timing chain replaced just after buying it, and about a month later, the head gasket blew out, complete with chocolate-milkshake-like stuff coming out of the tailpipe. I got that fixed, and the car ran OK for several months, and then it would periodically lose power and start running really badly.
A trip to the mechanic revealed the problem: when the head gasket blew out, it allowed cooling water into the crankcase. Apparently whoever replaced the head gasket did not do an oil change. So the water in the crankcase rusted out the main bearings. When they rusted out enough that there was a lot of slop in the crankshaft, the engine would make a lot of noise under load. This was enough to trigger the knock sensor, which is essentially a microphone, and it would mess with the fuel/air mixture, trying to make the noise go away. This caused the engine to lose power.
Rather than pouring more money into the car and replacing the main bearings, I just gave it to charity and bought another car.
My car radio problem starts with the sliding door in a van. The automatic door stopped working, so I checked the system and it wasn't the motor or switches. It was something with the board, so I took it out and thought I'd replace it. But at $600 used, I didn't bother. The kids went back to opening that door manually. (Radio is yet to come)
Next thing to go was the rear hatch controller. Okay we're not even touching that since I know the price already. Then the CD player in the radio stops working and won't even give my wife back her favorite ones. I'm definitely hating automotive electronics at this point, and figure I need to get something new soon.
Now comes the weird part. Ford has a recall on the torque converter. It's something mechanical that I understand. But when you're working near the starter you disconnect the battery to prevent accidentally shorting the contacts or anything else. So the shop had my vans battery disconnected for almost the entire day. A few days after we got the van back my wife thanks me for fixing the CD player. I said it wasn't me, and went out to check it myself. Sure enough it worked like nothing was ever wrong with it. That got me thinking about the battery, and figured the electronics needed to be completely powered off to let it reset. So on a whim I pushed the rear hatch button. It worked too! Now I only regret not leaving the sliding door's controller in place!
I know I'd had the battery disconnected for other work, but never for an extended period. That was what it needs for everything to reboot.
Older Jeeps (early to mid 1990's I believe) had a more insidious problem. The radio was on the engine data bus. If the radio had problems it could swamp/inhibit the bus and the vehicle would die. Not a nice "limp-home" mode, but "call the tow truck 'cause you aren't going anywhere" mode. Just a silly System's Engineering oversight (or cost savings), but with huge potential ramifications for customers. I guess you should consider yourself lucky.
As cars become more complicated (especially drive by wire systems), Systems Engineering becomes the critical link.
I had a similar incident occur one time with a Jeep Cherokee many years ago (probably 1999). I think the sensor systems were new then, but a check engine light ruined a trip i was taking with my then boyfriend, as it came on soon after we were driving at night from Phoenix to Utah. The car was new so we didn't know what it meant, even though the car was running fine. In the end it was something silly that triggered the light--sensor-related--and there was nothing wrong with the engine, but we turned around early in the trip and came home. Unfortunately, my CD player/car radio was stolen out of the jeep the next night! Had the check engine light not come on, we would have been away that weekend and it wouldn't have happened. So there you go! Not so much fun when this sort of glitch occurs.
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