What Does P0904 Mean?
The TCM has detected a general malfunction in the gate select position circuit, which monitors the left/right position of the shift mechanism in an automated manual transmission. This sensor tells the TCM which gear gate (plane) the shift fork is positioned in, enabling proper gear selection. A circuit fault means the TCM cannot determine the current gate position.
Safety Warning
Without accurate gate position data, the TCM cannot select the correct gear, potentially causing incorrect gear engagement or inability to shift. Do not drive until repaired.
Common Causes
35%
Failed gate select position sensor
30%
Open or damaged wiring between gate select sensor and TCM
20%
Corroded or loose connector at gate select sensor
15%
TCM internal circuit fault on gate select input
Diagnostic Steps
1
Step 1: Access the gate select position sensor on the transmission and inspect the connector for corrosion, moisture, or damage — clean and reseat if contamination is found.
2
Step 2: With key on engine off, measure the sensor supply voltage at the connector — expect 5V reference from TCM; absence indicates open supply wire or TCM fault.
3
Step 3: Monitor the gate select sensor output voltage with a scan tool while manually moving the selector (if possible) — signal should vary smoothly between 0.5V and 4.5V as the gate changes.
4
Step 4: Check the signal wire and ground wire for continuity from the sensor connector back to the TCM connector — resistance should be less than 5 ohms on each wire.
5
Step 5: If sensor, wiring, and connectors test good, the TCM gate select input circuit may be faulty — verify by checking for 5V reference at the TCM connector pins.
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
The TCM has detected a general malfunction in the gate select position circuit, which monitors the left/right position of the shift mechanism in an automated manual transmission. This sensor tells the TCM which gear gate (plane) the shift fork is positioned in, enabling proper gear selection. A circ...
The most common cause of P0904 (Gate Select Position Circuit [senses left / right position]) is: Failed gate select position sensor
Typical repair costs for P0904 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Without accurate gate position data, the TCM cannot select the correct gear, potentially causing incorrect gear engagement or inability to shift. Do not drive until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0904 to identify the root cause.
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Quick Info
Category
Powertrain
System
Automated Manual Transmission (Shift Control)
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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