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 P0900 to P0999 (Transmission Codes)

P0900....Clutch Actuator Circuit/Open

P0901....Clutch Actuator Circuit Range/Performance

P0902....Clutch Actuator Circuit Low

P0903....Clutch Actuator Circuit High

P0904....Gate Select Position Circuit

P0905....Gate Select Position Circuit Range/Performance

P0906....Gate Select Position Circuit Low

P0907....Gate Select Position Circuit High

P0908....Gate Select Position Circuit Intermittent

P0909....Gate Select Control Error

P0910....Gate Select Actuator Circuit/Open

P0911....Gate Select Actuator Circuit Range/Performance

P0912....Gate Select Actuator Circuit Low

P0913....Gate Select Actuator Circuit High

P0914....Gear Shift Position Circuit

P0915....Gear Shift Position Circuit Range/Performance

P0916....Gear Shift Position Circuit Low

P0917....Gear Shift Position Circuit High

P0918....Gear Shift Position Circuit Intermittent

P0919....Gear Shift Position Control Error

P0920....Gear Shift Forward Actuator Circuit/Open

P0921....Gear Shift Forward Actuator Circuit Range/Performance

P0922....Gear Shift Forward Actuator Circuit Low

P0923....Gear Shift Forward Actuator Circuit High

P0924....Gear Shift Reverse Actuator Circuit/Open

P0925....Gear Shift Reverse Actuator Circuit Range/Performance

P0926....Gear Shift Reverse Actuator Circuit Low

P0927....Gear Shift Reverse Actuator Circuit High

P0928....Gear Shift Lock Solenoid Control Circuit/Open

P0929....Gear Shift Lock Solenoid Control Circuit Range/Performance

P0930....Gear Shift Lock Solenoid Control Circuit Low

P0931....Gear Shift Lock Solenoid Control Circuit High

P0932....Hydraulic Pressure Sensor Circuit (Click Here for help diagnosing automatic transmission faults)

P0933....Hydraulic Pressure Sensor Range/Performance

P0934....Hydraulic Pressure Sensor Circuit Low

P0935....Hydraulic Pressure Sensor Circuit High

P0936....Hydraulic Pressure Sensor Circuit Intermittent

P0937....Hydraulic Oil Temperature Sensor Circuit

P0938....Hydraulic Oil Temperature Sensor Range/Performance

P0939....Hydraulic Oil Temperature Sensor Circuit Low

P0940....Hydraulic Oil Temperature Sensor Circuit High

P0941....Hydraulic Oil Temperature Sensor Circuit Intermittent

P0942....Hydraulic Pressure Unit

P0943....Hydraulic Pressure Unit Cycling Period Too Short

P0944....Hydraulic Pressure Unit Loss of Pressure

P0945....Hydraulic Pump Relay C ircuit/Open

P0946....Hydraulic Pump Relay C ircuit Range/Performance

P0947....Hydraulic Pump Relay C ircuit Low

P0948....Hydraulic Pump Relay C ircuit High

P0949....Auto Shift Manual Adaptive Learning Not Complete

P0950....Auto Shift Manual Control Circuit

P0951....Auto Shift Manual Control Circuit Range/Performance

P0952....Auto Shift Manual Control Circuit Low

P0953....Auto Shift Manual Control Circuit High

P0954....Auto Shift Manual Control Circuit Intermittent

P0955....Auto Shift Manual Mode Circuit

P0956....Auto Shift Manual Mode Circuit Range/Performance

P0957....Auto Shift Manual Mode Circuit Low

P0958....Auto Shift Manual Mode Circuit High

P0959....Auto Shift Manual Mode Circuit Intermittent

P0960....Pressure Control Solenoid "A" Control Circuit/Open

P0961....Pressure Control Solenoid "A" Control Circuit Range/Performance

P0962....Pressure Control Solenoid "A" Control Circuit Low

P0963....Pressure Control Solenoid "A" Control Circuit High

P0964....Pressure Control Solenoid "B" Control Circuit/Open

P0965....Pressure Control Solenoid "B" Control Circuit Range/Performance

P0966....Pressure Control Solenoid "B" Control Circuit Low

P0967....Pressure Control Solenoid "B" Control Circuit High

P0968....Pressure Control Solenoid "C" Control Circuit/Open

P0969....Pressure Control Solenoid "C" Control Circuit Range/Performance

P0970....Pressure Control Solenoid "C" Control Circuit Low

P0971....Pressure Control Solenoid "C" Control Circuit High

P0972....Shift Solenoid "A" Control Circuit Range/Performance

P0973....Shift Solenoid "A" Control Circuit Low

P0974....Shift Solenoid "A" Control Circuit High

P0975....Shift Solenoid "B" Control Circuit Range/Performance

P0976....Shift Solenoid "B" Control Circuit Low

P0977....Shift Solenoid "B" Control Circuit High

P0978....Shift Solenoid "C" Control Circuit Range/Performance

P0979....Shift Solenoid "C" Control Circuit Low

P0980....Shift Solenoid "C" Control Circuit High

P0981....Shift Solenoid "D" Control Circuit Range/Performance

P0982....Shift Solenoid "D" Control Circuit Low

P0983....Shift Solenoid "D" Control Circuit High

P0984....Shift Solenoid "E" Control Circuit Range/Performance

P0985....Shift Solenoid "E" Control Circuit Low

P0986....Shift Solenoid "E" Control Circuit High

P0987....Transmission Fluid Pressure Sensor/Switch "E" Circuit

P0988....Transmission Fluid Pressure Sensor/Switch "E" Circuit Range/Performance

P0989....Transmission Fluid Pressure Sensor/Switch "E" Circuit Low

P0990....Transmission Fluid Pressure Sensor/Switch "E" Circuit High

P0991....Transmission Fluid Pressure Sensor/Switch "E" Circuit Intermittent

P0992....Transmission Fluid Pressure Sensor/Switch "F" Circuit

P0993....Transmission Fluid Pressure Sensor/Switch "F" Circuit Range/Performance

P0994....Transmission Fluid Pressure Sensor/Switch "F" Circuit Low

P0995....Transmission Fluid Pressure Sensor/Switch "F" Circuit High

P0996....Transmission Fluid Pressure Sensor/Switch "F" Circuit Intermittent

P0997....Shift Solenoid "F" Control Circuit Range/Performance

P0998....Shift Solenoid "F" Control Circuit Low

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.