Detailed guide for MID 128 PID 100 FMI 3
Back to top ↑MID 128 PID 100 FMI 3 - Oil Pressure Sensor Circuit High Voltage
**Technical Background**: This fault sets when the ECM detects voltage on the signal circuit exceeding 4.95V (typical threshold) [citation:1]. The sensor is a 3-wire design with 5V reference, ground, and signal return [citation:2].
🔧 What's Actually Happening
The ECM expects a varying voltage between 0.5V (low pressure) and 4.5V (high pressure). When voltage goes above 4.95V, the ECM knows something's wrong electrically—either the sensor has failed internally shorted, or the wiring has contacted a voltage source it shouldn't.
🧪 Diagnostic Approach
**The "Unplug Test":**
1. Key OFF, disconnect sensor
2. Key ON, measure voltage at harness side signal pin
3. Should read about 5V (pull-up voltage) with sensor disconnected
4. If voltage is battery voltage (12V+), you have a short to power somewhere
**Common Culprits:**
- Chafed wiring near the turbo heat shield (common on D13) [citation:4]
- Oil intrusion into connector creating conductive paths
- Previous repairs where wires were spliced incorrectly
🖼️ Visual References
Search for these image types (royalty-free):
- "Chafed wire harness automotive" (generic wiring damage)
- "Oil pressure sensor connector with corrosion" (search on Flickr CC)
💡 Pro Tip
*"When diagnosing FMI 3 on any sensor, don't just check for shorts to battery—also check for OPEN ground circuits. If ground is missing, the signal wire can float up to reference voltage, mimicking a high voltage fault."* — Diesel electronics specialist
Mechanic community notes for MID 128 PID 100 FMI 3
Back to top ↑Real-world tips from technicians. Submissions are moderated to keep spam and “my cousin fixed it with duct tape” content out.
Share your fix / advice
Keep it useful: symptoms, what you checked, what fixed it, and whether the code stayed inactive after a drive cycle.