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.


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 P0600 to P0699

P0600....Serial Communication Link

P0601....Internal Control Module Memory Check Sum Error

P0602....Control Module Programming Error

P0603....Internal Control Module Keep Alive Memory (KAM) Error

P0604....Internal Control Module Random Access Memory (RAM) Error

P0605....Internal Control Module Read Only Memory (ROM) Error

P0606....ECM/PCM Processor (Click Here for help diagnosing PCM problems)

P0607....Control Module Performance

P0608....Control Module VSS Output 'A'

P0609....Control Module VSS Output 'B'

P0610....Control Module Vehicle Options Error

P0615....Starter Relay Circuit (Click Here for help diagnosing starter problems)

P0616....Starter Relay Circuit Low

P0617....Starter Relay Circuit High

P0618....Alternative Fuel Control Module KAM Error

P0619....Alternative Fuel Control Module RAM/ROM Error

P0620....Generator Control Circuit

P0621....Generator Lamp 'L' Terminal Control Circuit

P0622....Generator Field 'F' Terminal Control Circuit

P0623....Generator Lamp Control Circuit

P0624....Fuel Cap Lamp Control Circuit

P0630....VIN Not Programmed or Mismatch - ECM/PCM

P0631....VIN Not Programmed or Mismatch - TCM

P0635....Power Steering Control Circuit

P0836....Power Steering Control Circuit Low

P0637....Power Steering Control Circuit High

P0638....Throttle Actuator Control Range/Performance (Bank 1)

P0639....Throttle Actuator Control Range/Performance (Bank 2)

P0640....Intake Air Heater Control Circuit

P0645....A/C Clutch Relay Control Circuit

P0646....A/C Clutch Relay Control Circuit Low

P0647....A/C Clutch Relay Control Circuit High

P0648....Immobilizer Lamp Control Circuit

P0649....Speed Control Lamp Control Circuit

P0650....Malfunction Indicator Lamp (ML) Control Circuit

P0654....Engine RPM Output Circuit

P0655....Engine Hot Lamp Output Control Circuit

P0656....Fuel Level Output Circuit

P0660....Intake Manifold Tuning Valve Control Circuit (Bank 1)

P0661....Intake Manifold Tuning Valve Control Circuit Low (Bank 1)

P0662....Intake Manifold Tuning Valve Control Circuit High (Bank 1)

P0663....Intake Manifold Tuning Valve Control Circuit (Bank 2)

P0664....Intake Manifold Tuning Valve Control Circuit Low (Bank 2)

P0665....Intake Manifold Tuning Valve Control Circuit High (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. Please visit our forums for more detailed information on DTC trouble codes.