I'm hoping someone can lend a hand here.

This afternoon leaving work, I started up the car (2003 A4 F55 Coupe, 14,500 miles) and was immediately greeted by:
1. Reduced Engine Performance
2. Low Fuel
3. Shock Absorbers Inoperative
4. Service Vehicle Soon

I was able to put it gear and drive out of the parking lot, and further noticed that:
1. The windows (electric), HVAC (A/C), interior courtesy lamps, fog lamps, Active Handling, MSRC, and driver seat memory did not work.
2. Mirrors (electric), HVAC (outside air ventilate), turn signals, and HUD still worked.
3. Oil Pressure, Oil Temp, Water Temp, Tire Pressure, Instantaneous MPG, Range Remaining, and Fuel guages were all non functional.
4. Battery voltage read ~ 13.8 volts with the engine on, and ~12.9 volts with the engine off.

The whole way home, the DIC continually flashed Reduced Engine Performance. Resetting the message would only allow normal DIC functions to be displayed for a few seconds before Reduced Engine Performance would display again.

Upon getting home I tried to enter diagnostic display mode by the "options + 4 fuel" procedure.
Automatic diagnostics flashed all the relevant subsystems:
PCM, TCS, RTD, BCM, IPC, radio, HVAC, LDCM, RDCM, SCM, RFA, and each subsystem was listed as "NO COMM."
I.e.,
PCM...NO COMM
TCS...NO COMM
etc.

When it entered "Manual Diagnostics," I tried to read the codes per subsystem using 'Fuel' and 'Gages' and each subsystem was, again, listed as "NO COMM."

I then tried hooking up my Diablosport Predator to read the diagnostic codes. The Predator refused to connect to the car, continually asking me, "Is the ignition on?"

After this, I noticed that remote keyless entry was know not working either.

Bottom line, I can't read what codes are being thrown, and my Service manual insists that if the voltage across the OBD II port is within spec, then my scan tool is defective. I don't buy this.

Recent mods to the car:
1. Swapped out the OEM A/C Delco for an Optima Red Top 1/30/2005.

I have had zero mechanical/electrical problems with the car until this point.

Any help?

Update:
I noticed after my garage light had gone out that my brake lights still worked despite no key in the ignition. In addition, the driver side door control panel (windows, mirrors, memory, etc), PRND123, and HVAC indicators were all lit up, as if I were driving at night with the headlights on. Now, the trunk release does not work (either from FOB or inside the car), and the car will not start either. There is no clicking indicating that the starting motor is even attempting to turn over.

Fuelie driver:
The OEM Delco was fine and there were no signs of leaking when I replaced it. The replacement with the Optima was a preventative action.

I've disconnected the battery for now. The "always-on" behavior of the door control panel, PRND123, and HVAC has returned to expected behavior. The brake pedal is hard and has little give, which would indicate to me that the master cylinder is also completely off at this point.
I'll try BlueDragon's suggestion.

I'm really baffled at this point.

 

Whew! this is different, hard to tell. Disconnect your battery and wait for a half hour to an hour and reconnect. Make sure the connections are good. See what it does. Could be a loose ground, or something with the PCM. But the car does run and you can drive it?? Hum, no comm is usually low battery volts. The mirrors and door stuff run off the door control modules and that requires communications same as the other stuff. Could be a bad/poor ground???

being that you can't pull any codes?? Definately something in and around the PCM.

 

What condition was the old delco in when you replaced it. Did you check for possible leakage!!! The old battery could have been leaking on the PCM.

 

I had this exact set of symptoms. The cause was a bad PCM which had been damaged in a wreck. I replaced the PCM and now all is well. I am in no way trying to diagnose your problem, just relating my experience. BTW, my car is an '03 AE vert with F55 suspension.
Shirl

 

Obvious, I know, but check all the fuses.

 

with weird symptoms like that I would usually suspect the battery (which you have replaced...) or ground points (a 2003 should not be that bad yet), but in your case neither of them apply. I almost want to ask is your anti virus up to date, as this sounds like a virus of some sort.

I think you may end up at the stealer ofr a new PCM or BCM - one other thought is to PM Bill Curlee and see if he has any thoughts...

 

sounds like a fried bcm, check your floor and see if it is wet, this is what mine did, ac leaked down on the passanger floor and fried the bcm.

 

My bet is your BCM got wet! Check the carpets and jute underlayment for water or dampness. The BCM in in the passengers foot well under the toe board. It the shiney silver box.

Let us know how you make out.

Bill Curlee

 

So I tried BlueDragon's trick. And it worked...after some hair pulling.

For whatever reason, the ground terminal of my Optima is extremely sensitive. The ground wire needed to be torqued down to a very exact spot on the battery, no more, no less, before the car would start. Then I tried disconnecting and re-connecting again, and the second time, the torque didn't seem to matter.

Hmm...

In any case, it's running fine now, as if nothing had ever happened. Thank goodness. For a moment, I thought I was the proud owner of a finicky Italian exotic.

 

Wall Blow me down mate, I got one!
I put a new battery in my wife's Blazer a while back and the hot side of that the lip of the red rubber boot got squashed between the connection and made it intermitten as hell in damp weather. The alarm system thought somebody was trying to steal the car, and the computer shut everything off. It would start sometimes and sometimes not. With todays puters you get some strange results with bad grounds and electrical connections.

 

I learn something new everytime