Buying a PCM or ECM online? The key things to verify first — fitment, programming, warranty, and core charge — so you get a module that works.

Does a bad PCM cause a check engine light? What the light means, which codes point to the module, and how to tell a PCM fault from a sensor fault.

How long does a PCM or ECM last, what causes early failure, and how to protect your engine computer so it lasts the life of your vehicle.

Refurbished vs new PCM: the real differences in price, reliability, and warranty, and how to choose the right engine computer for your car.

Can you program a PCM yourself, or do you need a shop? What DIY programming requires, when it works, and the easier plug-and-play alternative.

How to reset your PCM or ECM, when a reset actually fixes a problem, and when it just masks a fault that needs a real repair or replacement.

GMC PCM problems on the Sierra and Acadia: common symptoms, why the module fails, and how a VIN-programmed replacement gets your GMC running right.

Toyota ECM problems on the Tundra and Sienna: symptoms to watch for, why the engine computer fails, and how a VIN-programmed replacement gets you back on the road.

Jeep PCM problems on the Wrangler and Grand Cherokee: common symptoms, why the powertrain control module fails, and how a VIN-programmed replacement fixes it.