Error Code P0908 is defined as Transmission Gate Select Position Circuit Intermittent. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to the present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
To monitor and tell the Powertrain Control Module (PCM) and Transmission Control Module (TCM) about the gear the transmission is in, automatic transmissions or automated manual transmissions use position sensor. The input data it receives is used to module engine power during gear shifts, control torque converter clutch slippage, and show the driver’s presently chosen gear.
Suppose the signal from the transmission gate selector position switch fails or fails intermittently. In that case, the PCM is unable to effectively control the gear shifts since the control module cannot detect which gear is selected. When the input data is a lot to the PCM, the Error Code P0908 will be set, and the Check Engine light will be activated. In some cases, the PCM will initiate the Limp Mode or failsafe mode to limit the engine power and protect the transmission.
This code may be accompanied by related GSP sensor codes, such as:
- Error Code P0904
- Error Code P0905
- Error Code P0906
- Error Code P0907
- Error Code P0909
- No start condition may be present
- Transmission may fail to engage (or some gears)
- Harsh shifting (erratic or unpredictable)
- Transmission may not shift at all, locked into failsafe or limp mode (until the problem is corrected)
- Faulty transmission fate selector position switch
- Misaligned or poorly adjusted transmission fate selector position switch
- Burnt, damaged, disconnected, or shorted wires
- Corroded connectors
- Excessive wear and free play in mechanical gear selector linkage
- Transmission malfunction (rare)
- Failed PCM or TCM (rare)
How to Check
Connect the OBD-II scanner to retrieve the freeze frame data.
Excessive free play, poor adjustment, and misaligned component in the mechanical linkage are the most common cause for this code. Thus, make sure you check the condition of the gear selector mechanism. Look for signs of damage such as excessive wear/free play and tightness of retaining bolts and screws.
Repair or replace any damaged components as needed. Clear the codes and take the vehicle for a test drive to check if the code comes back.
If the gear selector mechanism is in good condition, and the error code still comes back, refer to the wiring diagram and learn the function, color coding, and routing of the associated wirings.
Inspect the transmission gate selector switch and all related wirings. Look for signs of mechanical damage to the switch, and corrosion, short, or any forms of damages in the connectors or wirings. Perform necessary repairs (repair or replace damaged components) as needed. Clear the codes, then take the vehicle for a test drive to see if it comes back.
If there are no damages or defects in the wirings, check the manual for the details of the correct procedure to follow on resistance, ground integrity, and continuity tests for all relevant circuits.
Note: There is no one-size-fits-all approach for all vehicles, so make sure you refer to the manual for the exact locations of the circuits and switches.
Compare your readings from the values specified on the manual, make the necessary repair or replacements for the damaged connectors and/wirings to ensure the electrical values are within the ranges specified by the manufacturer.
Note: Since this code refers to an intermittent problem on the electrical components, it is entirely possible that this step may not show any issues and that all electrical values may still fall within the manufacturer’s specified values. Thus, it is important to wiggle the wires vigorously during continuity and resistance tests to induce the fault.
If the fault persists after the wiggle test, you can suspect a faulty transmission gear selector position switch. These switches cannot be repaired, which means you need to replace them with OEM (for reliable, long-term solution).
Note: Make sure the switch is aligned correctly when replacing and adjusting before using a thread-locking agent on the retaining bolts and screws. This is to prevent the switch from moving out of the position in the future.
Again, clear the codes and take the vehicle for a test drive to see if the code comes back. If the error code doesn’t come back immediately, then you may have successfully repaired the fault.
However, if the code comes back, repeat the electrical tests until you find the problematic component. If the code persists, it’s best to take it to a qualified mechanic for a more thorough and professional repair and replacement of large sections of the wirings.
How to Fix
- Replacement of faulty transmission fate selector position switch
- Repair or replacement of damaged wires or connectors
- Correction of switch alignment or adjustment
- Correction of excessive free play in mechanical linkages or components
Since it affects the drivability of the vehicle, this code is considered serious. Thus, it must be addressed as soon as possible to prevent further damage to the transmission. Ideally, vehicles with this code must not be driven since it poses safety risks.