Canon error codes
Canon uses a numbered error system across its EOS range. Err 01 usually points to a communication problem between the body and lens, often caused by dirty or corroded lens contacts. Err 20 and Err 30 indicate a mechanical shutter fault. Err 40 is a power-related fault, sometimes the battery system but also the power supply section of the main board. Err 70 and Err 80 indicate image sensor or card-related issues. The recurring Err 99 is a catch-all fault that can indicate anything from a lens contact fault to a failed mirror mechanism; Tim works through a structured exclusion process to identify the actual source.
Nikon fault indicators
Nikon DSLRs typically show an Err display in the top LCD or viewfinder rather than numbered codes. The most common causes are a shutter fault, an AF motor coupling problem, or a communication fault on the lens-body interface. Nikon Z-series mirrorless bodies have their own distinct fault indicators that differ from the DSLR range. Tim has diagnostic references for the full Nikon lineup and can identify which subsystem the indicator is pointing at.
Other makes
Sony, Fujifilm, Panasonic, and Olympus all use their own error and warning systems. Fujifilm X-series bodies occasionally show persistent warnings related to the focal plane shutter or the OIS unit. Panasonic Lumix bodies can display card read errors that are actually caused by the card slot flex cable rather than the card. Tim documents the fault code and cross-references it against the known failure patterns for that body before opening the camera.