Modern cars are complex machines, and their onboard computers are designed to monitor and regulate almost every engine function and other key systems. When something goes wrong, the computer triggers a check engine light (CEL) and stores a diagnostic trouble code (DTC) that can be read with a code reader. Among the codes that can appear are P0500, P0501, P0505, P0506, and P0507, which all relate to your vehicle’s speed sensor and idle control systems.
The P0500 code is triggered when the Engine Control Module
(ECM) detects an issue with the Vehicle Speed Sensor (VSS). This sensor
monitors the speed of your car's wheels and sends the data to the ECM, which
then uses this information for things like transmission shifting, ABS, and
speedometer function.
The P0501 code indicates that the vehicle speed sensor is
detecting values that are outside of the expected range. Like P0500, this could
affect how your vehicle shifts gears and performs at various speeds.
P0505 is triggered when the Idle Air Control (IAC) system
is not functioning as expected. The IAC valve controls the amount of air
entering the engine when the throttle is closed, ensuring a steady idle. If the
ECM detects a malfunction in the system, this code will appear.
Code P0506 appears when the engine idle speed is lower than
what the ECM expects. This typically points to an issue with the air entering
the engine at idle, often related to the IAC system.
On the opposite end of P0506, the P0507 code is triggered
when the engine idle speed is higher than expected. Again, this issue usually
stems from the Idle Air Control system or other factors that affect idle speed.