What does it mean?
As we know, the modern fuel injection and ignition system is a complex coordination of sensor readings and actuator outputs, all with the aim of delivering the most efficient power. The engine control module (ECM) uses various sensors to determine how much fuel to inject at any given moment, making precise calculations based on air flow and temperature, engine load and speed, driver demand, and a number of others.
Because the density of the fuel depends on its temperature, the ECM needs to take this into account when calculating fuel injector pulse. Without knowing fuel temperature, the ECM would command the same fuel delivery at all temperatures, resulting in richer or leaner combustion than ideal. On engines equipped with a fuel temperature sensor (FTS), this results in finer control of air-fuel ratio and lower emissions.
Earlier vehicles not equipped with an FTS achieved similar results using feedback from the AFR sensors. The ECM continually monitors the resistance of the FTS, calculating temperature based on those readings. If there is a fault in the FTS or FTS circuit, the ECM will illuminate the malfunction indicator lamp (MIL) and set a diagnostic trouble code (DTC) in memory. When P0186 is set, the PCM has determined that the input voltage from fuel temp sensor B is out of the normal range.
The vehicle has 2 fuel temperature sensors, and the “B” sensor is out of range. Note: A Range/Performance related code will be set when either a sensor or other component does not perform within the range the PCM (Powertrain Control Module) expects to see, given the current engine load/speed, and information gathered from other sensors.
The possible causes of Range/Performance codes are likely to be defective sensors as easily as they are likely to be the result of wiring issues that affect the operation of the affected sensor or component, which means that with these codes, it is important to regard all sensors and components as part of the control circuit the code refers to.