An interesting phenomenon occurred with a 2003 Honda Element equipped with a KA24 engine: the vehicle would only start and run when an OBD2 scanner was connected. This article explores the symptoms, diagnostic process, and potential reasons behind this unusual behavior.
The Element was initially towed to the shop and started without issue. After running for a few minutes and then being shut off, it refused to restart, only cranking without firing. During cranking, the instrument cluster gauges, specifically RPM and speedometer, exhibited erratic fluctuations. Connecting an Autel scan tool allowed the engine to start immediately, but it would die as soon as the scanner was disconnected.
A single diagnostic trouble code (DTC) was retrieved: P0606, indicating an ECM/PCM processor fault. Following the diagnostic procedure for this code, the ECM was replaced. However, the issue persisted even with the new ECM. The vehicle continued to exhibit the same behavior: starting only with the scanner connected and dying upon disconnection.
Further diagnostics revealed that the battery voltage was within the normal range, all ground connections under the hood were cleaned and re-secured, and all fuses in both fuse boxes were inspected and found to be functional. Live data readings while the engine was running appeared normal, except for the ELD (Electrical Load Detector) voltage, which read -0.19V instead of the expected ~20V. Although potentially unrelated, this anomaly was noted.
The core problem remains: why does the OBD2 scanner enable the engine to start and run? Several possibilities could explain this behavior. The act of connecting the scanner may provide a supplemental ground path, bypassing a faulty ground connection in the vehicle’s electrical system. This could allow the ECM to function correctly only when the scanner is plugged in. Alternatively, the scanner’s communication with the ECM might be temporarily overriding an internal fault within the ECM, allowing the engine to run. However, this doesn’t explain why a new ECM didn’t resolve the issue. Finally, there might be a problem with the immobilizer system. The scanner’s connection could be inadvertently bypassing the immobilizer, allowing the engine to start.
While the low ELD voltage reading might not be directly related to the starting issue, it warrants further investigation. A faulty ELD can cause various electrical problems, potentially contributing to the overall malfunction.
This case highlights the complexities of automotive diagnostics. While the P0606 code pointed to the ECM, replacing it didn’t solve the problem. The unusual behavior of the vehicle starting only with the OBD2 scanner connected suggests a deeper, underlying electrical issue that requires further investigation. Focusing on potential grounding problems, immobilizer system malfunctions, and a thorough diagnosis of the ELD circuit are recommended next steps.
