📖 What It Does
Together they manage the engine and transmission. The ECM/PCM handles spark, fuel, idle, and emissions. The TCM handles shift timing, line pressure, and torque converter lockup. They share data over CAN to coordinate things like shift-during-acceleration smoothness.
⚙ How It Works
Each module reads its own sensors, runs algorithms, and outputs commands to actuators. They communicate continuously over the CAN bus at 500 kbps or more. When you scan with an OBD2 tool, you are talking to one or more of these modules.
⚠ Symptoms When It Fails
Symptoms include intermittent stalling, no-start, harsh shifts, codes that come and go, or the entire dashboard going haywire. Common causes are water intrusion, voltage spikes from a bad alternator, or corroded module connectors. True module failure is rare.
💰 Replacement Cost
Replacement: $500–$2,000. A reman PCM runs $300–$800. Programming/flashing adds $100–$300 at a dealer. Some modules require security relearns.