Driver's intension to accelerate is transmitted to ECM through Accelerator Pedal Sensor (APS). And APS, whose mechanism is same as TPS, is required for ECM to determine optimum fuel injection quantity. As fidelity of APS is strongly required, APS is divided into two. One is APS1, which outputs main signals and the other is APS2, which monitors APS1 performance. APS1 and 2 do not share power supply and ground. Normally, APS2 output voltage is the half of APS1 and if the ratio of two signal is out of specified value, error is recognized then, Limp Home mode is activated. When Limp Home mode is activated, engine speed is fixed at 1200RPM and driving performance is limited to prevent excessive power generation due to APS false signal.

P2128 is set when output voltage of APS 2 is above the maximum value of 2.463V for more than 0.18 sec. This code is due to the short to battery in APS 2 power circuit and signal circuit or open in sensor ground circuit.

Fig.1) APS 1 signal and APS 2 signal are measured simultaneously, Check if output value is rising and APS 2 signal is 1/2 of APS 1 signal.

☞ APS 2 ground checking signal is for ECM to monitor APS 2. This signal drops APS 2 output voltage to below 200.39mV per 200msec. If APS 2 output voltage does not drop to below 200.39mV, ECM sets DTC as recognizing ground circuit error of APS 2 .