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P0904 is a diagnostic trouble code (DTC) for "Gate Select Position Circuit [senses left / right position]". 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. 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.
The P0904 code indicates that the electronic control module, or ECM, has detected a problem with the gate select position censor circuit. This code may also be accompanied by the P0905, P0906, P0907, or P0908 codes.
In most vehicles manufactured today, the TCM and ECM use various sensors to monitor and control the performance of the transmission. One of those sensors is the gate select position sensor, which tells the TCM and ECM what gear position the driver has put the vehicle in. These sensors are also used to monitor brake slippage and to detect clutch application in a manual vehicle. If the ECM is not receiving the correct signal from this sensor, it will register the P0904 code.
Most often, bad electrical connections within the circuit are to blame. This may include corroded or damaged wire harnesses, or loose connections. However, a misaligned sensor can also cause this issue. As a last resort, a faulty sensor may be suspected as the cause of the P0904 code.
Before the P0904 code is detected, the cruise control will usually stop working. In most cases, the Check Engine light will activate within two to three drive cycles after the PCM has detected the issue.
After an OBD-II scanner detects the P0904 code, a technician should begin by checking the alignment of the sensor. After a transmission repair, it is common for sensors to be misaligned. They may need to be rotated to a neutral baseline in order for the gate select position to be properly detected.
After this repair is performed, the mechanic should clear the code and retest the system. If the code reappears, they should then check all electrical components, looking for any loose, corroded, damaged, or otherwise faulty wiring or connectors. These should be replaced and then the system should be cleared and checked again.
If neither of these repairs gives the correct diagnosis, then the sensor is probably faulty.
When diagnosing the underlying cause of the P0904 code, the most common mistake is forgetting to disconnect the PCM and the cruise control module when testing circuit resistance. It is also important to clear the code and do a road test after each potential solution is attempted. If the most common repairs do not stop the Check Engine light from reappearing, it can be a sign of an intermittent issue that requires an in-depth inspection and servicing.
If the P0904 code is being detected, a vehicle should be repaired immediately. Without the ability to properly detect the gear, the vehicle can become unsafe to drive, or may become inoperable.
Repairs to address the P0904 code include:
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