Everything prints too light
Even, all-over faintness usually isn't a blocked nozzle. Check whether draft or economy mode was left on from the last long document, and check the paper type in the driver matches what's actually loaded, because the wrong setting lays down noticeably less ink. On a laser model, take the toner cartridge out and rock it gently side to side before you buy anything, since that redistributes what's left and often buys another few hundred pages.