P0991 is a Manufacturer Controlled Diagnostic Trouble Code (DTC) within the Powertrain (P) category. This code indicates an issue specific to the vehicle manufacturer's proprietary systems. The exact meaning and affected system depend on the make and model of your vehicle. When P0991 is stored in the engine control module (ECM), it means the onboard diagnostics have detected a malfunction or out-of-range condition in the Transmission - Manufacturer Controlled circuit or system.
P0991 is a Manufacturer Controlled Diagnostic Trouble Code (DTC) within the Powertrain (P) category. This code indicates an issue specific to the vehicle manufacturer's proprietary systems. The exact meaning and affected system depend on the make and model of your vehicle.
When P0991 is stored in the engine control module (ECM), it means the onboard diagnostics have detected a malfunction or out-of-range condition in the Transmission - Manufacturer Controlled circuit or system.
The information provided is for educational purposes only. Always consult a qualified mechanic for accurate diagnosis and repair. Diagnostic Trouble Codes can have multiple causes, and proper testing is essential before replacing parts.
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