DTC P1201: Actual Gas Flow Rate Does Not Match Desired Gas Flow Rate: Description

WARNING: This page is about a different car, the 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

Gas Mass Sensor (GMS) and Mixture Control Valve (MCV) are contained in one non-serviceable assembly. GMS monitors mass and flow of gaseous fuel entering engine and converts this information into a GMS actual gas flow signal circuit frequency. Alternate Fuel Engine Control Module (AF ECM) commands fuel flow by supplying MCV with a frequency signal. desired gas flow signal circuit frequency varies from 1050 Hz (0.40 gm/s) at idle, to 5000 Hz (18 gm/s) at wide open throttle.

AF ECM converts actual gas flow signal circuit frequency into a grams per second value. During low fuel flow rates (such as at engine idle) GMS sensor actual gas circuit will produce a low frequency signal of approximately 700 Hz (0.21 gm/s). During high fuel flow rates (such as at wide open throttle - road load) GMS sensor will produce a high frequency signal of approximately 2700 Hz (16.65 gm/s). AF ECM monitors and compares actual gas flow rate to a calculated gas flow rate. Calculated gas flow rate is based upon a calculated Mass Airflow (MAF) rate.

This DTC is used to indicate that the actual gas flow rate does not match a calculated gas flow rate.