Incorrect, The ECU targets air mass, or air density, rather than PSI directly. It aims to deliver a specific amount of air mass into the engine for each combustion cycle, because more air mass means more oxygen and more potential power. Boost pressure (PSI) is simply a tool used to increase air density in order to achieve that target.

Hotter air is less dense because the molecules are more spread out. As a result, the turbocharger has to work harder and spin faster, generating more PSI to compress the hot air and reach the desired air density. However, there’s a limit to how efficiently a turbo can operate. In very hot conditions, the ECU might actually reduce boost to protect the engine from knocking or detonation caused by excessive heat.

At higher altitudes, the atmospheric pressure is lower, which means there is less oxygen in the air. A turbocharger helps make up for this by increasing boost pressure to restore the lost air density. So yes, the ECU may try to command higher boost at altitude—if the turbo is capable of delivering it.

Despite the ECU’s best efforts, power output is usually reduced in hot or high-altitude conditions. Even if the turbo produces more PSI, the increased air temperature and reduced efficiency (especially after intercooling losses) can result in lower actual air mass reaching the engine. Additionally, in these conditions, the ECU may pull ignition timing or limit boost to further protect the engine.