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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.
Caution: If any other warning lights are on (temperature, charging system, oil pressure, etc.) and/or the engine is running abnormally (sputtering, misfiring badly, stalling, losing power) and/or is making any unusual noises or smells, STOP! The problem may be serious and could cause engine damage if the fault is not diagnosed and repaired.
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 or fault codes.
To read the trouble code(s) that are turning on your Check Engine light, you need a scan tool. This is a hand-held device that plugs into the 16-pin OBD II diagnostic connector under the instrument panel (usually near the steering column). On 1995 and older vehicles that do not have OBD II, the scan tool usually requires a special vehicle-specific diagnostic connector, and the connector may be located almost anywhere inside the vehicle or under the hood.
Many auto parts stores and even some repair shop will do a FREE plug in diagnosis to read out the codes. Most repair shops and dealerships, however, usually charge a flat diagnostic fee to perform a scan tool check.
Write down the code number(s). DO NOT erase the codes until you have written this information down because you will need it later to diagnose the problem.
The code(s) will tell you which sensors or systems are experiencing a problem. If the scan tool does not provide a definition, you will have to look up the code definition where ever you can find it (online, in a shop manual
The best (safest)way to erase trouble codes is to use a scan tool. The tool communicates with the vehicle computer and tells it to erase the codes. It does not alter any other learned settings that should be retained for normal vehicle operation.
The worst way to clear codes is to disconnect the battery. In most older vehicles (those made before 1996), disconnecting the battery even for a few seconds, or removing the power fuse for the engine computer (PCM) will erase the codes, along with all of the other learned settings the computer has stored over time.
NOTE: Clearing the codes will not keep the Check Engine light off. Sooner or later, the codes will reset and the Check Engine light will be back on UNLESS the problem(s) that caused the code(s) to set in the first place has been diagnosed and repaired.
Caution: Disconnecting the battery to clear codes on many 2006 and newer vehicles is NOT a good idea because it may cause the PCM to forget critical settings. This may have an adverse effect on the operation of the transmission, climate control system and other functions. This, in turn, may require special "relearn" procedures using a factory scan tool or professional grade scan tool to restore proper operation of the affected systems.
Note: Clearing codes with a scan tool, or disconnecting the battery will also reset all of the OBD system monitors back to zero, meaning your vehicle won't be accepted for an OBD plug-in emissions inspection until all of the monitors have run and completed (system ready).
Click Here for General Help with OBD2 Diagnostics
Click Here to go to Diagnostic Trouble Code Tips
Click Here for Most Common Trouble Codes (and what causes them)
Click Here for Oxygen Sensor Code Diagnosis
P0030, P0031, P0032, P0033, P0034, P0035, P0036, P0037, P0038
P0042, P0043, P0044, P0050, P0051, P0052, P0056, P0057, P0058
P0062, P0063, P0064, P0130, P0131, P0132, P0133, P0134, P0135
P0136, P0137, P0138, P0139, P0140, P0141, P0142, P0143, P0144
P0145, P0146, P0147
Click Here for Mass Airflow (MAF) Sensor Code Diagnosis
P0100, P0101, P0102, P0103, P0104, P0171, P0172, P0173, P0174, P0175
Click Here for Coolant Sensor Code Diagnosis
P0115, P0116, P0117, P0118, P0119
Click Here for P0171 & P0174 Lean Code Diagnosis
Click Here for P0300 Random Misfire Code Diagnosis
Click Here for Engine Misfire Code Diagnosis
P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0309, P0310, P0311, P0312
Click Here for Crankshaft Position (CKP) or Camshaft Position (CMP) Sensor Diagnosis
CKP codes: P0335, P0336, P0337, P0338, P0339
CMP codes: P0340, P0341, P0342, P0343, P0344, P0345, P0346, P0347, P0348, P0349
Click Here for Exhaust Gas Recirculation (EGR) Code Diagnosis
P0400, P0401, P0402, P0403, P0404, P0405, P0406, P0407, P0408, P0409
Click Here for Catalytic Converter Code Diagnosis
P0420, P0421, P0422, P0423, P0424, P0425, P0426, P0427, P0428, P0429
P0430, P0431, P0432, P0433, P0434, P0435, P0436, P0437, P0438, P0439
Click here for Evaporative Emission Control (EVAP)Code Diagnosis
P0440, P0441, P0442, P0443, P0444, P0445, P0446, P0447, P0448,P0449
P0450, P0451, P0452, P0453, P0454, P0455, P0456, P0457
Chrysler Powertrain Fault Codes P1100 to P1399
Chrysler Powertrain Fault Codes P1400 to P1899
Ford Powertrain Fault Codes P1000 to P1299
Ford Powertrain Fault Codes P1300 to P1499
Ford Powertrain Fault Codes P1500 to P1699
Ford Powertrain Fault Codes P1700 to P1999
GM Powertrain Fault Codes P1000 to P1299
GM PowertrainFault Codes P1300 to P1499
GM Powertrain Fault Codes P1500 to P1699
GM Powertrain Fault Codes P1700 to P1899
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Check Engine Light On? Need Trouble Code Help? 