P0904: Gate Select Position Circuit Malfunction
The P0904 code indicates a problem in the gate select position circuit of an automated manual transmission (AMT) or dual-clutch transmission (DCT). This circuit monitors the position of the gear selector gate to ensure proper gear engagement. A fault can cause incorrect gear selection, leading to transmission performance issues.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission stuck in gear or unable to shift
- Harsh or delayed gear engagement
2. Most Common Causes
- Faulty gate select position sensor
- Open or short circuit in the signal, reference (5V), or ground wiring
- Corroded, loose, or damaged connector terminals at the sensor or TCM/PCM
- Internal TCM/PCM failure (uncommon)
- Misadjusted or damaged shift linkage mechanism
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional codes.
Step 2: Visually inspect the gate select position sensor and its wiring for damage or corrosion.
Step 3: Test the sensor's voltage and resistance per manufacturer specifications.
Step 4: If sensor and wiring are okay, check the TCM for faults or perform a relearn procedure.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended as the transmission may fail to shift properly, leading to unsafe driving conditions.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on the part and labor.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.