MID 128 PID 103 FMI 9: Turbocharger Speed Sensor - Signal Lost (Volvo)

MID 128 PID 103 FMI 9 - Turbo Speed Signal Lost

**Technical Detail**: This fault logs when the turbo speed sensor signal is completely lost [citation:3]. Without turbo speed input, the ECM cannot properly control the VGT or protect against overspeed.

📍 Sensor Location

The Turbo Speed Sensor is mounted in the center of the turbocharger and reads directly from the turbo shaft (not the vanes) [citation:8].

🔧 Why It Fails

**Common Failure Modes:**

1. **Sensor electrical failure** (internal open/short)

2. **Wiring damage** (heat from turbo, chafing)

3. **Connector issues** (corrosion, melted plastic)

4. **Tone wheel damage** (rare, but possible if turbo had debris)

🧪 Diagnosis

**Visual Inspection:**

• Look for melted or brittle wiring near turbo
• Check connector for heat damage
• Inspect for oil leaks contaminating sensor

**Electrical Tests:**

• Check for 5V supply (or battery voltage depending on sensor type)
• Verify ground circuit
• Test signal with oscilloscope if available (should show square wave)

🛠️ Parts & Images

The turbo speed sensor is often specific to the turbo model. Use OEM Volvo parts—aftermarket sensors for this application are notoriously problematic.

**Free images:**

• "Turbo speed sensor" (generic automotive sensor)
• "Turbocharger center housing" (shows sensor mounting location)

⚠️ Important Note

On some Volvo applications, this fault may also trigger if the ECM doesn't receive expected CAN messages from other modules (unlikely, but possible). Check for communication faults elsewhere.

Without turbo speed signal, the ECM enters a default boost control mode that may limit performance significantly.