Detailed guide for MID 128 PID 26 FMI 3
Back to top ↑MID 128 PID 26 FMI 3 - Fan Speed Percent
**Fault Type:** Voltage above normal or shorted to high source
Fault Condition
- Missing signal from Fan Speed Sensor
- Short Circuit + (Measuring line)
- Short Circuit - (Measuring line)
- Open Circuit (Measuring line)
- Open Circuit (Ground line)
Possible Symptoms
- Higher fuel consumption
- Fan will work as on/off only (100% fan speed if cooling is needed)
Possible Causes
- Cooling Fan Speed (CFS) sensor failure
- Faulty Cooling Fan Speed (CFS) sensor harness
Sensor Location
The Cooling Fan Speed (CFS) Sensor is located in the fan drive on the front of the engine.
Diagnostic Tips
1. Inspect the Cooling Fan Speed sensor and its wiring harness
2. Check for shorts to battery or ground in the measuring line
3. Verify continuity in both measuring and ground lines
4. Use Premium Tech Tool (PTT) to monitor fan speed signal
5. On engines with electronically controlled viscous fan drive, the electronic fan drive contains a Hall effect speed sensor
Mechanic community notes for MID 128 PID 26 FMI 3
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