Detecting Condition
WARNING: This page is about a different car, the 2004 Suzuki XL-7 and 2004 Suzuki Grand Vitara. However, it is still accessible from the selected car via links, so may be relevant.
When abnormality on the idle speed control signal, the engine power control signal or so on outputted from TCM is detected by ECM, ECM sets DTC P1603. (TCM outputs the trouble code to ECM when TCM cannot compute the engine control signal due to malfunctions of sensor circuits used for gear shift control.)