What does the diagnostic computer communication failure mean for an old Audi A6?
3 Answers
Old Audi A6 diagnostic computer communication failure means the engine control unit cannot communicate. Reasons for diagnostic computer communication failure: The control unit-J104 on the CAN bus does not match the engine control software version at all. The engine control unit malfunctions. CAN bus failure. These two CAN buses swap positions. Control units transmitting signals via the CAN bus. Solutions: Measure oil pressure at idle, low pressure 450kPa, high pressure 4MPa, normal. Inspect the intake system and find deformation and cracking in the intercooler of the turbocharging system. While driving, the boosted air is bypassed before entering the engine intake, reducing the actual air intake, naturally causing the mixture to be too rich.
I've repaired quite a few Audis over the years, especially the older A6 models. When the diagnostic computer can't connect, it basically means the OBD port in the car isn't communicating with external devices. This could be due to rusty pins causing poor contact in the interface, or the diagnostic tool's connector being too loose. Sometimes, if the battery voltage is too low—below 10 volts—communication will also fail. Additionally, the K-line communication protocol in older cars isn't compatible with today's universal protocols, requiring specialized equipment. The most troublesome issue is when the gateway module burns out, which requires removing the dashboard to fix. My suggestion is to first check if the interface has water damage or corrosion, then try replacing the battery with a fully charged one. If that doesn't work, you'll need to find a specialized Audi repair shop to read the fault codes.
Last time I helped my friend with his 2000 A6, I encountered this exact situation. The diagnostic tool showed no response at all, with the interface displaying 'Communication Failure'. It was actually a chain reaction caused by aging circuits in older vehicles: first, oxidation on the battery terminals caused unstable power supply, then poor contact on pin 16 of the diagnostic port, and finally we found swollen capacitors inside the gateway module. These older cars are particularly vulnerable to wiring modifications - if aftermarket alarms or subwoofers were installed and the wiring grounded improperly, it could interfere with communication. I remember one case where a small 7.5A fuse in the fuse box had blown - replacing it immediately restored communication.
