A failing powertrain control module (PCM) can cause a variety of issues, including poor engine performance, stalling, rough idling, and other symptoms. Some warning signs of a failing PCM may include:

1. Check engine light: A malfunctioning PCM can trigger the check engine light to come on.

2. Poor performance: If your car is struggling to accelerate, has a rough idle, or is stalling frequently, it could be a sign of a failing PCM.

3. Engine misfires: A failing PCM can also cause engine misfires, which can result in a loss of power and poor vehicle performance.

4. Transmission issues: A damaged PCM can also cause issues with your car's transmission, including shifting problems and difficulty maintaining speed.

If you suspect that your car's PCM is failing, it's important to have it diagnosed and repaired by a qualified mechanic to prevent further damage to your vehicle.