08/28/2026
2015 Jaguar XJR — Intermittent No-Crank/No-Start Diagnostic
This XJR came in with an intermittent no-crank/no-start condition, warning lights across the dashboard, and 125 communication-related fault codes stored across multiple modules, including the ECM, TCM, BCM, ABS, and fuel system.
After verifying that both batteries were healthy, we tested the vehicle’s communication networks at the diagnostic connector. The high-speed bus showed an intermittent open circuit. Using an oscilloscope, we were able to view the CAN communication signals directly. The medium-speed network was communicating normally, while the high-speed CAN network was intermittently dropping out.
Using the wiring diagrams, we began isolating sections of the high-speed network. Disconnecting the main communication connector between the interior and the engine bay restored communication, narrowing the fault to the engine-bay side of the network.
From there, we disconnected the ECM and ABS individually, with no change. Once the TCM was unplugged, communication immediately returned to normal. We repeated the test several times to confirm the failure.
Final diagnosis: a failed TCM/mechatronic unit was intermittently taking down the high-speed CAN network.
This is why proper electrical diagnostics matter. At Skyline, we don’t guess. Through years of combined experience, proper tooling, and ongoing education, we get to the root cause of even the most complicated issues.
