Check Mode
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) has the ability to operate in the Normal mode or in the Check mode. The 2 modes of operation are similar. When the PCM is operating in the Check mode, PCM has an increased ability to detect malfunctions. The most significant feature of the Check mode operation is that all "B" type codes now run like "A" type codes. In order to request that the PCM operate in the Check mode, scan tool communication with the PCM is necessary.