MID 128 PID 100 FMI 5: Engine Oil Pressure Sensor - Open Circuit (Volvo)

MID 128 PID 100 FMI 5 - Oil Pressure Sensor Open/Low Current

**Technical Detail**: This fault triggers when signal voltage drops below 0.08V, indicating either an open circuit or a short to ground [citation:1][citation:2].

🔍 The "Open Circuit" Reality

FMI 5 is the electrical version of a "disconnected" fault. The ECM sees no signal current because:

• The wire is broken somewhere
• The sensor is unplugged
• The wire is shorted directly to ground

🧪 Diagnosis by the Numbers

**Using a multimeter:**

1. Key OFF, disconnect sensor

2. Check resistance between sensor signal pin and ground:

• Should be high (open circuit) with sensor disconnected

3. Check continuity of 5V supply from ECM to sensor

4. Check continuity of ground circuit from ECM to sensor

**On Volvo D13:**

The oil pressure sensor harness often rubs against the engine block near the turbocharger [citation:4]. After 500k miles, the insulation wears through and wires can break or short.

📸 Image Search Terms

• "Broken wire harness abrasion" (generic automotive)
• "Engine harness chafing repair" (shows typical damage)

👨‍🔧 Real Mechanic Wisdom

*"When I see FMI 5 on an oil pressure sensor, I start by looking for physical damage. Had a truck where a rat chewed through three wires—took 10 minutes to find, 30 minutes to repair, saved customer $1000 in unnecessary parts."* — Mobile truck repair

⚡ Quick Verification

If you jumper signal to ground at the sensor connector (with key ON), the voltage should drop to near 0V and the fault should change (or you'll see 0 pressure in data). This confirms wiring to ECM is intact.