MID 128, PID 26 Estimated Percent
FMI 3 – Voltage above normal or shorted high
Fault code explanation: The fan speed sensor signal is missing.
Fault indication: Yellow alarm status.
Fault stored in memory: Yes.
Symptom: Fan will work as an ON/OFF fan. Full fan speed will be set if cooling is needed.
Conditions for fault code: The engine ECU is not receiving a valid fan speed sensor signal.
DTL = 5000 ms
Possible reason: • Open circuit in the fan speed sensor wiring.
Faulty fan speed sensor.
Suitable action: 1 Check all cables and connectors between the engine ECU and the fan
2 Check the sensor.
speed sensor is a Hall effect sensor and when
the fan rotates the sensor receives impulses (6 pulses/
The output signal from the fan speed sensor, pin E on
sensor connector to pin A35 on the engine ECU, is a
voltage signal which is proportional to the fan speed.
Pin A7 on the engine ECU provides pin A at the sensor
connector with an operating voltage of +5 V. Pin D at
the sensor connector is connected to battery negative
via pin A39 on the engine ECU.
The fan clutch engagement is controlled by engine
ECU. The clutch solenoid is energized with a PWM
signal by the engine ECU pin B49.
Sensor Engine ECU Signal type
E A35 square wave (sensor out-
D A39 bat- (sensor supply -)
B - bat+
C B49 PWM (low side switch)
A A7 +5V (sensor supply +)
30-2 Fault Tracing
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