The B1491 Code is important to know and get the accurate meaning of the code. The code has a meaning and the dictionary meaning is important to know. The dictionary meaning is B for Body Code Problem is antilock brake system, electronic suspension and steering systems. 1 for MFG – Manufacturer Specific. 4 for Transmission. 9 for Crankshaft Position Sensor Circuit Performance and 1 for TFP Valve Position Switch-Drive Without Drive Ratio. The catalytic converter contains an oxygen sensor in front and behindhand it. When the car is hot and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate.