Porsche 964 Airbag ScanTool Investigation: No Module Response, Diagnosis Unresolved
C24FUN documents a 1990 964 C2 airbag-warning investigation. After commenters disagreed about whether wakeup should use the K or L line, the author modified the interface and still reported no response from the airbag module on either line.
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Warning lights after an earlier loss of communication
C24FUN identifies his car as a 1990 C2. About a year before the post, his ScanTool had stopped communicating with the airbag controller, without an airbag warning at the time. Later, during acceleration, the seat-belt, airbag and master-warning lights came on. The engine appeared to run normally to him; that observation did not establish that the restraint system was working. His ScanTool could still communicate with the Motronic and climate-control units.
Conflicting advice about K and L
ToreB said the airbag controller uses K for wakeup and data, and supplied a simplified interface schematic. mojorizing later said a stock 964 uses L for wakeup and K for data, questioning the interface and connector arrangement. These conflicting participant explanations do not establish a wiring specification. The owner’s eventual test on both lines is more useful here than choosing one reply as settled fact.
Scope traces compare responding and silent modules
The owner modified his interface to select K or L for the outgoing wakeup and added scope monitoring points. His ECU and climate-control traces show L-line wakeup followed by K-line data. In the airbag comparison, the wakeup attempts repeat without a reply. He suspected a controller communication fault or the final wiring section, but did not establish either as the cause. His proposed two-fault explanation—an older communication failure and a newer warning-triggering event—also remained a hypothesis.
Continuity checks narrowed the investigation without proving a repair
C24FUN reported the controller number as 964 618 217 03. A later inspection of the cable termination let him report continuity of K and L from the diagnostic plug into the controller. He still could not detach the harness connection and stopped rather than risk damaging it. This account does not validate a controller-opening procedure, identify a failed component or establish interchangeability with a later module.
Neither wakeup choice restored communication
In his follow-up, C24FUN confirmed trying wakeup on both K and L many times: the airbag controller gave no response either way, while the ECU and climate-control units continued to respond with L-line wakeup. He reported fitting an SRS bypass to suppress the warning lights, explicitly saying it was not the solution he wanted. Suppressed lights are not evidence that the airbag fault was repaired or restraint protection restored. A subsequent ground-check suggestion remained a commenter’s proposal, with no confirming result in this account.
Another car’s resoldering result stays separate
uli1266 linked a clock-repair article and reported that resoldering had resolved the airbag-light issue on their own 964. C24FUN replied that he had already done that work preventively. It therefore supplies context for a suggestion he had already tried, rather than a successful repair of his no-response condition.