Almost every aspect of modern life involves some sort of interaction with an electronic device that's essentially a computer. From smartphones to PCs, vehicles to electronics, we all use these tools and toys to work, play, and in the case of some medical devices, survive. The recent chip shortage highlights our dependence on microprocessors in a number of daily applications. Known by many acronyms from PCM, ECM, ECU to TCM and BCM, vehicle computers use input from multiple sensors to make decisions about how to keep the vehicle running correctly throughout a wide range of conditions, and then send their own signals to various actuators, modules, and solenoids. You can think of these as if-then functions. If the PCM or powertrain control module receives signal X from a particular sensor, then it's programming prompts it to do Y. If it doesn't receive this particular signal, it may do nothing, or if it receives a different signal, then it does Z. At its heart, a PCM operates in binary language, which is a series of ones and zeros that can represent a yes or no answer to a question. This same logic can be applied to the CANBUS or controller area network by broadcasting these yes-no signals along two channels between the dozens of individual ECUs so they can share information. Each module can choose to accept or ignore these signals based on some programming. When something goes wrong, the PCM logs a fault known as a pending code. If that pending code isn't seen again for 40-50 drive cycles, it goes away. If it happens in two consecutive drive cycles, it matures into a stored or active code and the check engine lamp illuminates. A steady check engine light simply shows a stored fault as present, while a flashing light indicates a serious misfire condition that may cause severe drivability issues or catalytic converter damage. Analyzing the stored 5-digit codes will lead the technician to the possible root causes of the fault. These are grouped into several categories, each representing a subsystem. The most common ones are P or power train codes, but B or body codes and C for chassis codes also can show up in scan reports when faults exist in HVAC, Restraint, or ABS systems. In most cases, the PCM or other ECU is simply reporting a fault found among the incoming sensor information. But codes at P0 600-610 are associated with problems within the PCM circuitry itself. These are the most likely scenarios when PCM replacement becomes necessary. When a customer does meet at replacement PCM, identifying and selecting the correct unit is critical. The original part number and application, as well as any calibration codes and vehicle options, should be determined before ordering their replacement. Depending on the application, additional on-vehicle flashing may be required for the vehicle to become mobile again. This may include VIN and mileage programming, calibration updates, and even a re-learn period. Most aftermarket PCMs are offered as remanufactured units, so a rebuildable core of the same or equivalent part number is often required. For obsolete or uncommon units, R and R of the customer's original unit may be the own replacement option, which often involves shipping the existing failed unit to a rebuilder and waiting for it to be processed and returned. In any case, accurate diagnosis of the failure is critical so that the replacement PCM actually solves the problem. PCMs often are replaced as a last-ditch, Hail Mary effort, when a number of other solutions have failed. So, alleged defective returns should be processed carefully. When they're sensitive electronics and the VIN-specific programming required of most modern PCMs, these units should be considered non-returnable final sales. All customers, especially DIYers, should be fully informed of any additional programming requirements and your own store policies before ordering any of these modules. Thanks for watching.