Intermittent fault codes are trouble codes caused by a problem that is present only some of the time. The check engine light may come on for a few days and then go out, or a code may appear in memory even though the car seems to run perfectly when you inspect it. These faults frustrate … Read more
Short circuit trouble codes appear when a control module detects current taking a path it was never meant to take. Instead of flowing through the intended component, the current finds a shortcut to ground, to a power source, or into a neighboring wire, and the module records the abnormal condition. Shorts deserve prompt attention because … Read more
Open circuit trouble codes are set when a control module detects that an electrical path it monitors is no longer complete. Somewhere between the module and the component, current has stopped flowing the way it should, and the module flags that loss as a stored fault. An open can be a wire broken inside its … Read more
Circuit high and low codes are diagnostic trouble codes that tell you an electrical signal has moved outside the limits the engine computer expects to see. They are among the most common codes a basic scan tool will show, and they point to a wiring or sensor circuit problem rather than a worn mechanical part. … Read more
Actuator circuit trouble codes are set when the engine computer detects that an output device it controls, such as a fuel injector, ignition coil, solenoid, motor or relay, is not responding electrically the way it should. These codes describe the control side of a system rather than the sensing side. Understanding how a module drives … Read more
Sensor circuit trouble codes are set when the engine computer sees a signal from a sensor that is missing, stuck, outside its expected range or inconsistent with other data. Because the computer can only judge the signal it receives, the fault may lie in the sensor, its wiring, its connector or the module itself. This … Read more
Communication bus trouble codes signal that the data network linking a vehicle’s control modules is not carrying messages properly. Diagnosing them is a process of elimination, moving from the simplest causes toward the network wiring until the point of failure is found. This guide lays out a practical diagnostic approach for these faults. It covers … Read more
Airbag trouble codes are stored by the supplemental restraint system (SRS) module when it detects a fault in the airbags, seat belt pretensioners, crash sensors, wiring or its own circuits. When a fault is present, the airbag light stays on and some or all restraint devices may not deploy in a crash. That makes these … Read more
ABS trouble codes are stored by the anti-lock brake system module when it finds a problem with a wheel speed sensor, a hydraulic valve, the pump motor, its power supply or its communication with other modules. When that happens, the ABS warning light usually turns on and anti-lock function may be disabled. Normal braking typically … Read more
Transmission trouble codes are stored when the module that manages an automatic transmission detects a fault in its sensors, solenoids, hydraulic performance or gear ratios. On many vehicles that module is a separate transmission control module, or TCM; on others, transmission control is built into the PCM. These codes matter because transmissions often protect themselves … Read more