Is your "Check Engine Light" on? An illuminated "Malfunction Indicator Lamp" (or MIL ) means a fault has been detected in the engine control system and one or more "diagnostic trouble codes" (DTCs) are stored in the engine's computer. Depending on the nature of the fault, the lamp may come on and go off, remain on continuously or flash. Some types of intermittent faults will make the lamp come on only while the fault is occurring. When the fault goes away, the lamp goes off. Other types of problems will turn the light on, and it will remain on until the fault is diagnosed and repaired.
The Check Engine lamp has proven to be a great annoyance to many motorists (as well as professional technicians) because it seems to have a mind of its own. For one thing, it doesn't tell you anything about the nature of the problem or what the trouble code might be. It could be something serious - or it might not. There is no way to know without performing a diagnostic test on the system. Consequently, you don't know if you should stop immediately or ignore the light and keep driving. If no other warning lights are on, and the engine seems to be running normally (no unusual noises, smells, vibrations, etc.), it is probably safe to assume the problem is minor and won't hinder your ability to continue driving. But sooner or later, you should have the cause of the light investigated.
Whenever the Check Engine light comes on, a "diagnostic trouble code" (DTC) or fault code is recorded in the powertrain control module (PCM) memory. The trouble code has a number that corresponds to the type of fault. Some problems can generate more than one trouble code, and some vehicles may suffer from multiple problems that also set multiple trouble codes.
SETTING TROUBLE CODES
In most older vehicles (those made before 1996), disconnecting the computer power source or disconnecting a battery cable could erase fault codes -- at least temporarily until the trouble code resets and turns the check engine light back on. But on many newer vehicles, you do NOT want to disconnect the battery because doing so can wipe out the computer's memory settings as well as the trouble codes. This may affect the operation of the transmission, climate control system and other functions.
In most newer computer systems, fault codes are stored in a "nonvolatile" memory that is not lost if the battery is disconnected. The trouble codes remain intact until they are cleared using a scan tool
Diagnostic Trouble Code numbers are read by plugging a code reader or scan tool into the vehicle diagnostic connector (usually located under the instrument panel near the steering column). The presence of a code will turn on the Check Engine Light. The light will remain on until the code has been erased. The code number does not tell you which part has failed. It only indicates a possible fault has been detected in the circuit, system or sensor described. Further testing is usually required to isolate the fault BEFORE repairs are made. For diagnostic charts and vehicle specific repair information, refer to a service manual, or the OEM technical website
DTC CODES P0400 to P0499
P0400....Exhaust Gas Recirculation Flow
P0401....Exhaust Gas Recirculation Flow Insufficient Detected
P0402....Exhaust Gas Recirculation Flow Excessive Detected
P0403....Exhaust Gas Recirculation Control Circuit
P0404....Exhaust Gas Recirculation Control Circuit Range/Performance
P0405....Exhaust Gas Recirculation Sensor 'A' Circuit Low
P0406....Exhaust Gas Recirculation Sensor 'A' Circuit High
P0407....Exhaust Gas Recirculation Sensor 'B' Circuit Low
P0408....Exhaust Gas Recirculation Sensor 'B' Circuit High
P0409....Exhaust Gas Recirculation Sensor 'A' Circuit
P0410....Secondary Air Injection System
P0411....Secondary Air Injection System Incorrect Flow Detected
P0412....Secondary Air Injection System Switching Valve 'A' Circuit
P0413....Secondary Air Injection System Switching Valve 'A' Circuit Open
P0414....Secondary Air Injection System Switching Valve 'A' Circuit Shorted
P0415....Secondary Air Injection System Switching Valve 'B' Circuit
P0416....secondary Air Injection System Switching Valve 'B' Circuit Open
P0417....secondary Air Injection System Switching Valve 'B' Circuit Shorted
P0416....Secondary Air Injection System Relay 'A' Circuit
P0419....Secondary Air injection System Relay 'B' Circuit
P0420....Catalyst System Efficiency Below Threshold (Bank 1) Click Here for diagnostic help on P0420 converter codes
P0421....Warm Up Catalyst Efficiency Below Threshold (Bank 1)
P0422....Main Catalyst Efficiency Below Threshold (Bank 1)
P0423....Heated Catalyst Efficiency Below Threshold (Bank 1)
P0424....Heated Catalyst Temperature Below Threshold (Bank 1)
P0425....Catalyst Temperature Sensor (Bank 1)
P0426....Catalyst Temperature Sensor Range/Performance (Bank 1)
P0427....Catalyst Temperature Sensor Low Input (Bank 1)
P0428....Catalyst Temperature Sensor High Input (Bank 1)
P0429....Catalyst Heater Control Circuit (Bank 1)
P0430....Catalyst System Efficiency Below Threshold (Bank 2)
P0431....Warm Up Catalyst Efficiency Below Threshold (Bank 2)
P0432....Main Catalyst Efficiency Below Threshold (Bank 2)
P0433....Heated Catalyst Efficiency Below Threshold (Bank 2)
P0434....Heated Catalyst Temperature Below Threshold (Bank 2)
P0435....Catalyst Temperature Sensor (Bank 2)
P0436....Catalyst Temperature Sensor Range/Performance (Bank 2)
P0437....Catalyst Temperature Sensor Low Input (Bank 2)
P0438....Catalyst Temperature Sensor High Input (Bank 2)
P0439....Catalyst Heater Control Circuit (Bank 2)
P0440....Evaporative Emission Control System (Click Here for help diagnosing EVAP faults )
P0441....Evaporative Emission Control System Incorrect Purge Flow
P0442....Evaporative Emission Control System Leak Detected (small leak)
P0443....Evaporative Emission Control System Purge Control Valve Circuit
P0444....Evaporative Emission Control System Purge Control Valve Circuit Open
P0445....Evaporative Emission Control System Purge Control Valve Circuit Shorted
P0446....Evaporative Emission Control System Vent Control Circuit
P0447....Evaporative Emission Control System Vent Control Circuit Open
P0448....Evaporative Emission Control System Vent Control Circuit Shorted
P0449....Evaporative Emission Control System Vent Valve/Solenoid Circuit
P0450....Evaporative Emission Control System Pressure Sensor
P0451....Evaporative Emission Control System Pressure Sensor Range/Performance
P0452....Evaporative Emission Control System Pressure Sensor Low Input
P0453....Evaporative Emission Control System Pressure Sensor High input
P0454....Evaporative Emission Control System Pressure Sensor Intermittent
P0455....Evaporative Emission Control System Leak Detected (gross leak)
P0456....Evaporative Emission Control System Leak Detected (very small leak)
P0457....Evaporative Emission Control System Leak Detected (fuel cap loose/off)
P0460....Fuel Level Sensor Circuit
P0461....Fuel Level Sensor Circuit Range/Performance
P0462....Fuel Level Sensor Circuit Low Input
P0463....Fuel Level Sensor Circuit High Input
P0464....Fuel Level Sensor Circuit Intermittent
P0465....EVAP Purge Flow Sensor Circuit
P0466....EVAP Purge Flow Sensor Circuit Range/Performance
P0467....EVAP Purge Flow Sensor Circuit Low Input
P0468....EVAP Purge Flow Sensor Circuit High Input
P0469....EVAP Purge Flow Sensor Circuit Intermittent
P0470....Exhaust Pressure Sensor
P0471....Exhaust Pressure Sensor Range/Performance
P0472....Exhaust Pressure Sensor Low
P0473....Exhaust Pressure Sensor High
P0474....Exhaust Pressure Sensor Intermittent
P0475....Exhaust Pressure Control Valve
P0476....Exhaust Pressure Control Valve Range/Performance
P0477....Exhaust Pressure Control Valve Low
P0478....Exhaust Pressure Control Valve High
P0479....Exhaust Pressure Control Valve Intermittent
P0480....Cooling Fan 1 Control Circuit
P0481....Cooling Fan 2 Control Circuit
P0482....Cooling Fan 3 Control Circuit
P0483....Cooling Fan Rationality Check
P0484....Cooling Fan Circuit Over Current
P0485....Cooling Fan Power/Ground Circuit
P0486....Exhaust Gas Recirculation Sensor 'B' Circuit
P0487....Exhaust Gas Recirculation Throttle Position Control Circuit
P0488....Exhaust Gas Recirculation Throttle Position Control Range/Performance
P0491....Secondary Air Injection System (Bank 1)
P0492....Secondary Air Injection System (Bank 2)
Remember that these Automotive DTC trouble codes are just a starting point, further diagnostics will be required to find the root cause of the check engine light and the setting of the trouble code
