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P0921 is a diagnostic trouble code (DTC) for "Gear Shift Forward Actuator Circuit Range/Performance". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $79.99. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
When the Powertrain Control Module (PCM) detects a problem with the gear shift forward actuator circuit, a P0921 trouble code is stored. Other related trouble codes include a P0920, P0922, P0923, P0924, P0925, P0926, and P0927 trouble code.
The P0921 trouble code is stored when the PCM detects a variation in the voltage coming from the gear shift forward actuator circuit that is outside the normal limits set by the vehicle manufacturer. In addition, the Check Engine light illuminates with the storage of this code.
Some potential causes of a P0921 trouble code include a faulty gear shift forward actuator, shorted or defective wiring and connectors, a defective gear guide rail, and a defective shift shaft. A mechanical failure within the transmission can also cause storage of this code. In rare cases, a faulty PCM or Transmission Control Module (TCM) can also cause this code.
Some of the symptoms that accompany a P0921 trouble code include difficulty or the inability to shift into a forward-moving gear. Another symptom of a P0921 trouble code is a reduction in fuel efficiency.
Diagnosis of a P0921 trouble code by a mechanic is accomplished through the use of an advanced scanner and a digital volt/ohm meter. The mechanic should keep in mind to address the trouble codes in the order they were stored. The easiest way to accomplish this is to download any freeze frame data and any stored trouble codes. When diagnosing a P0921 trouble code, a mechanic should perform the following:
A mistake often made by mechanics when diagnosing a P0921 trouble code is to not clear codes in the order they were stored. In addition, mechanics might also replace components that are not at fault instead of faulty wiring or connectors, resulting in a failure to fix the problem.
While a vehicle that has a P0921 trouble code stored on its PCM might still be drivable, more than likely continued use of the vehicle without getting the code fixed can result in drivability issues over time. It is best to get the P0921 trouble code fixed to prevent failure of the vehicle to shift into a forward-moving gear.
To fix and clear a P0921 trouble code, the mechanic needs to perform the following repairs:
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