Audi A8MMI black failure

Audi A8 sedan, a 2005 annual output of the 4.2L engine code BFM, the customer repair MMI black screen.

Pick-up: First, GM Tech2connect the computer detects Fibre open fault code within the gateway, the use of diagnostic loop is interrupted diagnosis by conventional thinking, the circuit diagnosis (Figure 2), in order to further confirm the reasons for the failure of the Ring Break Diagnosis, analysis can not be its principle, the ring break diagnosis began after the diagnostic management through diagnostic line to the control unit sends a pulse. This pulse so that all control units light-emitting unit emits light signal conduction emission (FOT). In this process, all the control unit checks its own power supply and its internal electronic control and from the ring bus before a control unit on the light receiving signal.

Diagnostic manager identification system through which information can be optical data transfer between the electrical failure (power supply failure), or which of the two control unit interrupt, X431so the reasons for the failure of the Ring Break Diagnosis: ① gateway failure; ② diagnostic line short-circuit fault;. MM} system control unit failure.

To further confirm the reason unplug the CD plugs measurement diagnosis line voltage value (activated MMI system), a voltage value close to 0, proved diagnosis line at failure. Measuring 4 feet voltage gateway (4 feet for the diagnosis line first, activate the MMI) close to 12V, the gateway diagnostic functions properly, the questions focused on the diagnostic line or control unit, from the investigation and the line to start taking into account more cumbersome, so selection starting from the control ELM327 unit, the control unit an internal short circuit will result in this case, then sequentially cut off the control unit of the plug connector, while measuring the voltage value of the diagnostic line, when disconnecting the telephone control unit, the the diagnostic line voltage value returned to normal, replace the telephone control unit with fiber replacement and troubleshooting.

Black screen failure in the MMI control unit caused by damage to the fiber optic disconnect through the loop diagnostics as well as fiber optic alternative is to determine the specific point of ecu チューニングfailure, but in this case in the diagnostic line short circuit fault is really a very rare treat this failure must be departure from the principle of relying on logical thinking gradually seeking to identify the point of failure.