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

P0100....Mass or Volume Air Flow Circuit

P0101....Mass or Volume Air Flow Circuit Range/Performance Problem

P0102....Mass or Volume Air Flow Circuit Low Input

P0103....Mass or Volume Air Flow Circuit High Input

P0104....Mass or Volume Air Flow Circuit Intermittent

P0105....Manifold Absolute Pressure/Barometric Pressure Circuit (Click Here for help diagnosing MAP sensor faults)

P0106....Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem

P0107....Manifold Absolute Pressure/Barometric Pressure Circuit Low Input

P0108....Manifold Absolute Pressure/Barometric Pressure Circuit High Input

P0109....Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent

P0110....Intake Air Temperature Circuit (Click Here for help diagnosing air temperature sensor faults)

P0111....Intake Air Temperature Circuit Range/Performance Problem

P0112....Intake Air Temperature Circuit Low Input

P0113....Intake Air Temperature Circuit High Input

P0114....Intake Air Temperature Circuit Intermittent

P0115....Engine Coolant Temperature Circuit ( Click Here for diagnostic help with coolant sensor faults)

P0116....Engine Coolant Temperature Circuit Range/Performance Problem

P0117....Engine Coolant Temperature Circuit Low Input

P0118....Engine Coolant Temperature Circuit High Input

P0119....Engine Coolant Temperature Circuit Intermittent

P0120....Throttle/Pedal Position Sensor/Switch A Circuit (Click Here for help diagnosing throttle-by-wire systems)

P0121....Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem

P0122....Throttle/Pedal Position Sensor/Switch A Circuit Low Input

P0123....Throttle/Pedal Position Sensor/Switch A Circuit High Input

P0124....Throttle/Pedal Position Sensor/Switch A Circuit Intermittent

P0125....Insufficient Coolant Temperature for Closed Loop Fuel Control

P0126....Insufficient Coolant Temperature for Stable Operation

P0127....Intake Air Temperature Too High

P0128....Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

P0130....O2 Sensor Circuit (Bank 1 Sensor 1) ( Click Here for diagnostic help with oxygen sensor faults)

P0131....O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)

P0132....O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)

P0133....O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)

P0134....O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)

P0135....O2 Sensor Heater Circuit (Bank 1 Sensor 1)

P0136....O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)

P0137....O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)

P0138....O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)

P0139....O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)

P0140....O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

P0141....O2 Sensor Heater Circuit (Bank 1 Sensor 2) ( Click Here for diagnostic help with oxygen sensor faults)

P0142....O2 Sensor Circuit Malfunction (Bank 1 Sensor 3)

P0143....O2 Sensor Circuit Low Voltage (Bank 1 Sensor 3)

P0144....O2 Sensor Circuit High Voltage (Bank 1 Sensor 3)

P0145....O2 Sensor Circuit Slow Response (Bank 1 Sensor 3)

P0146....O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 3)

P0147....O2 Sensor Heater Circuit (Bank 1 Sensor 3)

P0148....Fuel Delivery Error

P0149....Fuel Timing Error

P0150....O2 Sensor Circuit (Bank 2 Sensor 1) ( Click Here for diagnostic help with oxygen sensor faults)

P0151....O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)

P0152....O2 Sensor Circuit High Voltage (Bank 2 Sensor 1)

P0153....O2 Sensor Circuit Slow Response (Bank 2 Sensor 1)

P0154....O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)

P0155....O2 Sensor Heater Circuit (Bank 2 Sensor 1)

P0156....O2 Sensor Circuit Malfunction (Bank 2 Sensor 2)

P0157....O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

P0158....O2 Sensor Circuit High Voltage (Bank 2 Sensor 2)

P0159....O2 Sensor Circuit Slow Response (Bank 2 Sensor 2)

P0160....O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)

P0161....O2 Sensor Heater Circuit (Bank 2 Sensor 2)

P0162....O2 Sensor Circuit Malfunction (Bank 2 Sensor 3)

P0163....O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)

P0164....O2 Sensor Circuit High Voltage (Bank 2 Sensor 3)

P0165....O2 Sensor Circuit Slow Response (Bank 2 Sensor 3)

P0166....O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 3)

P0167....O2 Sensor Heater Circuit (Bank 2 Sensor 3)

P0168....Fuel Temperature Too High

P0169....Incorrect Fuel Composition

P0170....Fuel Trim (Bank 1)

P0171....System too Lean (Bank 1) ( Click Here for diagnostic help on Ford P0171 codes)

P0172....System too Rich (Bank 1)

P0173....Fuel Trim Malfunction (Bank 2)

P0174....System too Lean (Bank 2) ( Click Here for diagnostic help on Ford P0174 codes)

P0175....System too Rich (Bank 2)

P0176....Fuel Composition Sensor Circuit

P0177....Fuel Composition Sensor Circuit Range/Performance

P0178....Fuel Composition Sensor Circuit Low Input

P0179....Fuel Composition Sensor Circuit High Input

P0180....Fuel Temperature Sensor A Circuit

P0181....Fuel Temperature Sensor A Circuit Range/Performance

P0182....Fuel Temperature Sensor A Circuit Low Input

P0183....Fuel Temperature Sensor A Circuit High Input

P0184....Fuel Temperature Sensor A Circuit Intermittent

P0185....Fuel Temperature Sensor B Circuit

P0186....Fuel Temperature Sensor B Circuit Range/Performance

P0187....Fuel Temperature Sensor B Circuit Low Input

P0188....Fuel Temperature Sensor B Circuit High Input

P0189....Fuel Temperature Sensor B Circuit Intermittent

P0190....Fuel Rail Pressure Sensor Circuit

P0191....Fuel Rail Pressure Sensor Circuit Range/Performance

P0192....Fuel Rail Pressure Sensor Circuit Low In put

P0193....Fuel Rail Pressure Sensor Circuit High Input

P0194....Fuel Rail Pressure Sensor Circuit Intermittent

P0195....Engine Oil Temperature Sensor

P0196....Engine Oil Temperature Sensor Range/Performance

P0197....Engine Oil Temperature Sensor Low

P0198....Engine Oil Temperature Sensor High

P0199....Engine Oil Temperature Sensor Intermittent

Get more information on these automotive trouble codes on our forums, always there and always free