Technical Description of OBD-II Trouble Code
No Signal in Fan Speed Sensor Circuit
This powertrain code is a generic OBD-II trouble code that applies to all vehicle makes and models (1996-newer). However, the specific repair steps may vary depending on the model.
What does that mean?
Some vehicles have a sensor at the end of the cooling fan that detects movement during vehicle operation. This sensor is used to determine if the fan is running on a vehicle with a fan clutch, or to verify the fan speed commanded by the Powertrain Control Module (PCM) or Engine Control Module (ECM) matches the actual fan speed detected on a vehicle with an electric fan.
The sensor used is a 3-wire, hall effect sensor that receives a 5-volt reference source from the PCM, along with a ground wire and a signal wire to determine fan speed. A P0528 code indicates that the PCM/ECM has detected a fault with the sensor or wiring.
Note: Be cautious when handling an electric fan, as it may turn on even when the vehicle is not operating. This code is similar to P0526, P0527, and P0529.
Symptoms
Symptoms of a P0528 trouble code may include:
Causes
Possible causes of a P0528 code include:
Possible Solutions
Fan Clutch equipped – Visually inspect the fan while the engine is running to ensure it is spinning. If the fan is not spinning, it may be due to a broken accessory belt or a failed fan clutch assembly. Replace the accessory belt or fan clutch assembly.
Electrical Fan equipped – Verify that the fan turns on and off when the PCM/ECM commands it to operate at certain temperatures. The fan may automatically turn on when the air conditioner is activated. If the fan is not operating, check the electrical harness connector, fuses, or relays that control the electric fan. Some fans may be activated by an on/off relay or by Pulse Width Modulation (PWM) with variable speed fans. Repair the electrical fan circuit, replace the electric fan assembly, fan motor, or driver module as necessary.
Cooling fan sensor harness – Check for loose connections and damaged wiring that may have come into contact with the cooling fan. Disconnect the cooling fan sensor connector and the connector at the PCM, then use a Digital Volt Ohm Meter (DVOM) to check for resistance by placing the leads at each end of the signal wire. Some vehicle manufacturers have issued a Technical Service Bulletin (TSB) for replacing the sensor wiring harness. Replace or repair the harness as needed.
PCM/ECM – Disconnect the fan speed sensor harness and the PCM/ECM harness. Use a DVOM with positive and negative leads connected to each end to check for excessive resistance in the signal wire circuit. Back-probe the signal wire using a DVOM set to the volts scale or a graphing multimeter at the sensor harness and the PCM/ECM. Place the positive lead on the signal wire and the negative lead on a known good ground to determine if the voltage is present from the fan speed sensor. If the signal is present but not received by the PCM/ECM, replace the PCM/ECM.
Cooling fan speed sensor – Disconnect the harness connector from the sensor and test for continuity using the DVOM set to the Ohms scale between the power, ground, and signal wires. There should be no resistance between the signal wire and either the ground or power wires. If resistance is present, there may be an internal short.
The signal wire can only be tested during actual fan operation by back-probing the harness connector with the DVOM set to the volts scale or a graphing multimeter. Place the positive lead on the signal wire and the negative lead on a known good ground. The hall effect sensor used operates by creating a magnetic field that changes voltage while the fan is spinning. As the fan speed increases, the voltage should also increase. Replace the cooling fan speed sensor if it is determined to be faulty.
