The technician investigated an intermittent no-start issue on a 2001 Porsche 911 Carrera 2 using Autel MaxiSys MS908S Pro II diagnostic scanner. The owner reported that turning the ignition only produced a click, and the engine would crank only after repeated attempts.
A weak battery was suspected, so the battery was charged and live data was monitored. A fault code P1571 Immobilizer appeared during a quick scan with MS908S Pro II. After clearing the code, the engine started normally several times, indicating that the immobilizer system might not consistently authorize the start.
Next, the battery terminals were inspected and found to be heavily oxidized. Cleaning the terminals improved voltage stability, but the intermittent problem still occurred occasionally.
The technician then examined the alarm/immobilizer control module under the seat. Using a multimeter and oscilloscope, he verified voltage supply and observed data pulses on the immobilizer communication wire. The oscilloscope revealed periodic data signals and confirmed proper operation of the relay involved in the immobilizer circuit.
Even after checking wiring continuity to the ECU and inspecting for moisture around connectors, no definitive electrical failure was found.
Finally, replacing the old battery resolved the issue completely. The engine started flawlessly every time, proving that unstable battery voltage had disrupted immobilizer communication and prevented cranking.
This case reinforces an important diagnostic rule: always confirm battery health before pursuing deeper electrical or immobilizer troubleshooting