Modern vehicles are complex machines, and when the check engine light illuminates, it often signals the need for a diagnostic tool. OBD2 scanners have become indispensable for car owners and mechanics alike, offering a window into a vehicle’s health by reading trouble codes. However, what happens when using an OBD scanner seems to cause more problems than it solves? This was the perplexing experience of a Nissan Altima owner.
Initially, the 2000 Nissan Altima was stalling during acceleration, although it would restart, albeit with continued stalling under load. The “Service Engine Soon” light was active, prompting the owner to seek a diagnosis. A friend’s OTC scanner was connected, but surprisingly, after this connection, the car refused to start at all and no error codes could be retrieved. The issue seemed to escalate from intermittent stalling to a complete no-start condition simply after plugging in a diagnostic tool.
Troubleshooting began the next day, and miraculously, the car started again. A fuel filter and oil change were performed. For a short period, the Altima ran smoothly, only to stall again. Further investigation, including online research, led to the discovery of a vacuum hose damaged by rodents. Repairing this hose appeared to resolve the stalling issue, and while the “Service Engine Soon” light remained on, the car seemed to be running normally. The vacuum leak was likely the culprit behind the initial stalling and the warning light.
With the car running once more, the friend returned with the OTC scanner to read the stored error codes. This time, codes P0100, P0505, P0325, P1490, P0446, and P0464 were successfully retrieved. However, the act of connecting the OBD scanner once again caused an unexpected problem: the car stalled and would not restart, mirroring the previous incident. It appeared the scanner was somehow interfering with the vehicle’s operation.
Further research revealed a potential explanation: OBD scanners can sometimes disrupt the Engine Control Module (ECM), necessitating a hard reset. This reset can be performed by disconnecting both battery terminals and briefly connecting them together for about 10 seconds (ensuring they are disconnected from the battery). This process discharges capacitors in the ECM, effectively resetting it. After performing this hard reset, the Nissan Altima was able to start again.
This case highlights the generally beneficial nature of OBD scanners for diagnosing car problems, while also illustrating a less common, but important consideration. In rare instances, connecting an OBD scanner can lead to unexpected issues, potentially due to ECM interference. Knowing how to perform an ECM hard reset can be a valuable troubleshooting step if you encounter a similar situation where your car malfunctions immediately after connecting a diagnostic scanner.
