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 light 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 P0800 to P0899 (Transmission Codes)

P0801....Reverse Inhibit Control Circuit

P0803....1-4 Upshift (Skip Shift) Solenoid Control Circuit

P0804....1-4 Upshift (Skip Shift) Lamp Control Circuit

P0805....Clutch Position Sensor Circuit (Click Here for help diagnosing clutch problems)

P0806....Clutch Position Sensor Circuit Range/Performance

P0807....Clutch Position Sensor Circuit Low

P0808....Clutch Position Sensor Circuit High

P0809....Clutch Position Sensor Circuit Intermittent

P0810....Clutch Position Control Error

P0811....Excessive Clutch Slippage

P0812....Reverse Input Circuit

P0813....Reverse Output Circuit

P0814....Transmission Range Display Circuit

P0815....Upshift Switch Circuit

P0816....Downshift Switch Circuit

P0817....Starter Disable Circuit

P0818....Driveline Disconnect Switch Input Circuit

P0820....Gear Lever X-Y Position Sensor Circuit

P0821....Gear Lever X Position Circuit

P0822....Gear Lever Y Position Circuit

P0823....Gear Lever X Position Circuit Intermittent

P0824....Gear Lever Y Position Circuit Intermittent

P0825....Gear Lever Push-Pull Switch (Shift Anticipate)

P0830....Clutch Pedal Switch 'A' Circuit

P0831....Clutch Pedal Switch 'A' Circuit Low

P0832....Clutch Pedal Switch 'A' Circuit High

P0833....Clutch Pedal Switch 'B' Circuit

P0834....Clutch Pedal Switch 'B' Circuit Low

P0835....Clutch Pedal Switch 'B' Circuit High

P0836....Four Wheel Drive (4WD) Switch Circuit

P0837....Four Wheel Drive (4WD) Switch Circuit Range/Performance

P0838....Four Wheel Drive (4WD) Switch Circuit Low

P0839....Four Wheel Drive (4WD) Switch Circuit High

P0840....Transmission Fluid Pressure Sensor/Switch 'A' Circuit

P0841....Transmission Fluid Pressure Sensor/Switch 'A' Circuit Range/Performance

P0842....Transmission Fluid Pressure Sensor/Switch 'A' Circuit Low

P0843....Transmission Fluid Pressure Sensor/Switch 'A' Circuit High

P0844....Transmission Fluid Pressure Sensor/Switch 'A' Circuit Intermittent

P0845....Transmission Fluid Pressure Sensor/Switch 'B' Circuit

P0846....Transmission Fluid Pressure Sensor/Switch 'B' Circuit Range/Performance

P0847....Transmission Fluid Pressure Sensor/Switch 'B' Circuit Low

P0848....Transmission Fluid Pressure Sensor/Switch 'B' Circuit High

P0849....Transmission Fluid Pressure Sensor/Switch 'B' Circuit Intermittent

P0850....Park/Neutral Switch Input Circuit

P0851....Park/Neutral Switch Input Circuit Low

P0852....Park/Neutral Switch Input Circuit High

P0853....Drive Switch Input Circuit

P0854....Drive Switch Input C ircuit Low

P0855....Drive Switch Input Circuit High

P0856....Traction Control Input Signal (Click Here for help diagnosing traction control faults)

P0857....Traction Control Input Signal Range/Performance

P0858....Traction Control Input Signal Low

P0859....Traction Control Input Signal High

P0860....Gear Shift Module Communication Circuit

P0861....Gear Shift Module Communication Circuit Low

P0862....Gear Shift Module Communication Circuit High

P0863....TCM Communication Circuit

P0864....TCM Communication Circuit Range/Performance

P0865....TCM Communication Circuit Low

P0866....TCM Communication Circuit High

P0867....Transmission Fluid Pressure (Click Here for help diagnosing automatic transmission faults)

P0868....Transmission Fluid Pressure Low

P0869....Transmission Fluid Pressure High

P0870....Transmission Fluid Pressure Sensor/Switch "C" circuit

P0871....Transmission Fluid Pressure Sensor/Switch "C" Circuit Range/Performance

P0872....Transmission Fluid Pressure Sensor/Switch "C" circuit Low

P0873....Transmission Fluid Pressure Sensor/Switch "C" circuit High

P0874....Transmission Fluid Pressure Sensor/Switch "C" circuit Intermittent

P0875....Transmission Fluid Pressure Sensor/Switch "D" circuit

P0876....Transmission Fluid Pressure Sensor/Switch "D" Circuit Range/Performance

P0877....Transmission Fluid Pressure Sensor/Switch "D" circuit Low

P0878....Transmission Fluid Pressure Sensor/Switch "D" circuit High

P0879....Transmission Fluid Pressure Sensor/Switch "D" circuit Intermittent

P0880....TCM Power Input Signal

P0881....TCM Power Input Signal Range/Performance

P0882....TCM Power Input Signal Low

P0883....TCM Power Input Signal High

P0884....TCM Power Input Signal Intermittent

P0885....TCM Power Relay Control Circuit/Open

P0886....TCM Power Relay Control Circuit Low

P0887....TCM Power Relay Control Circuit High

P0888....TCM Power Relay Sense Circuit

P0889....TCM Power Relay Sense Circuit Range/Performance

P0890....TCM Power Relay Sense Circuit Low

P0891....TCM Power Relay Sense Circuit High

P0892....TCM Power Relay Sense C ircuit Intermittent

P0893....Multiple Gears Engaged

P0894....Transmission Component Slipping

P0895....Shift Time Too Short

P0896....Shift Time Too Long

P0897....Transmission Fluid Deteriorated (Click Here for information about automatic transmission fluid)

P0898....Transmission Control System MIL Request Circuit Low

P0899....Transmission Control System MIL Request Circuit High

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.