A no-start condition in cold weather led to a frustrating diagnostic journey, ultimately revealing a self-inflicted issue related to the TCM (Throttle Control Module) fuse and a previously removed fuse tap. The vehicle initially presented with a crank-no-start condition and a DTC related to the ignition system. This problem only occurred in sub-freezing temperatures.
Pinpointing the Problem: From Ignition Switch to Fuse Box
The initial diagnosis pointed towards a faulty ignition switch, which was replaced without resolving the issue. Further troubleshooting involved warming various components, including the PCM (Powertrain Control Module), BCM (Body Control Module), and the fuse box. Applying heat to the fuse box temporarily restored engine function, suggesting a temperature-sensitive issue within that area.
Removing the fuse box cover often caused the engine to stall or exhibit reduced power. Testing individual relays did not reveal a faulty component. However, manipulating the fuses led to a breakthrough. Wiggling the 15-amp TCM fuse resulted in engine shut down, despite the fuse itself being functional.
The Culprit: A Loose Fuse Connection
Closer inspection revealed a loose connection on the forward leg of the TCM fuse. This loose connection stemmed from a previous removal of a fuse tap that had been installed on that particular fuse. While removing the seemingly unnecessary fuse tap seemed harmless in warmer weather, the colder temperatures caused the fuse leg to contract, resulting in poor contact and intermittent engine operation.
The Solution: Repairing the Fuse Connection
The solution involved adding solder to the loose fuse leg to ensure a secure and reliable connection. This simple fix resolved the no-start condition and cleared the associated DTC. The ignition switch replacement proved unnecessary, highlighting the importance of thorough diagnostics.
Lessons Learned and Lingering Questions
This experience underscored the importance of carefully considering the potential consequences of even minor modifications to the vehicle’s electrical system. While removing the fuse tap initially seemed like a preventative measure, it ultimately created a temperature-dependent failure point. The root cause of the dead Aux power #2 remains unresolved, suggesting further investigation into the socket or its connections is necessary. This case study demonstrates how a seemingly simple problem can have a complex and unexpected root cause, emphasizing the need for methodical troubleshooting.
