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Error Code P0528 is defined as Speed Sensor Circuit No Signal. In other definitions, it’s called “Speed Sensor Circuit Malfunction,” which is pretty much the same.
This code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
Some vehicles come with a special sensor called cooling fan speed sensor to detect movement during the operation of the vehicle. This sensor determines the fan clutch or verifies the fan speed as commanded by the PCM (powertrain control module, also known as the ECM or engine control module), to match the actual fan speed detected on an electric fan equipped vehicle.
This sensor has three wires that use 5V reference source coming from the PCM, a ground wire, and a signal wire to the PCM to read the fan speed.
When the Error Code P0528 is triggered, that means the PCM has determined a fault in either the sensor or wiring, causing a no signal or malfunction for the speed sensor circuit.
Other related error codes include:
- Error Code P0526
- Error Code P0527
- Error Code P0529
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:
- Vehicle running hotter than usual
- A/C not working properly
The most common cause for this code is a defective cooling fan motor or fault in the fan relay. Other possible causes include:
- Defective fan clutch or electric fan
- Open circuit in the cooling fan sensor connector or harness
- Broken accessory belt
- Defective PCM (rare)
How to Check
As with most codes, the first step for diagnosis for this would be to check if there are other codes present in the PCM as well. These codes should be addressed in the order that they appear. Collect these trouble codes and record their freeze frame data.
Next, with the key off, check the cooling fan; rotate it manually to see if there’s any mechanical binding issue. If the fan checks out fine, check the cooling fan clutch’s operation. This is done by turning on the engine with the heater off and monitoring the PCM for its RPMs.
If necessary, check for resistance in the cooling fan clutch actuator valve solenoid between the cooling fan clutch connectors, including the solenoid’s voltage.
Other issues you need to check for include:
For Fan Clutch Equipped
Make sure the fan is spinning correctly while the engine is running. If it’s not, then it may be caused by failed clutch assembly or, broken accessory belt. Replace as necessary.
For Electrical Fan Equipped
Check whether the fan is turning on and off when the PCM commands the fan to run when the engine reaches a certain temperature. In many cases, the fan may be automatically activated when the AC is turned on. If the fan is not running, check the electrical harness, fuses, or relays that operate the electric fan. Some fans may be turned on using an on/off relay or activated by the PVM (pulse width modulation), with variable speed fans. Replace electric fan assembly, electrical fan circuit, motor or fan module, if equipped.
For Cooling Fan Sensor Harness
Check the wiring and connectors that may have come in contact with the cooling fan. Look for signs of damages. Unplug the cooling fan sensor connector and the connector at the PCM. Use your DVOM (digital volt ohm meter) to check for resistance. Use leads at each end of the power wire, signal wire, and ground (if connected to the PCM). Some manufacturers provide TSB (technical service bulletin for the proper procedure of sensor wiring harness replacement. Repair or replace harness as necessary.
To Check the PCM
With KOEO (key on engine off) unplug the harness connector at the cooling fan sensor and then check for 5V reference source from the PCM. Set the DVOM at volts scale and use the wiring diagram for reference; place positive lead on the power wire and negative lead to a known good ground. Then, use the DVOM’s positive lead connected to a known good power source to check for ground and the negative lead at harness ground wire. If no reference voltage is being supplied, then it’s time to replace the PCM.
To Check the Cooling Fan Speed Sensor
Disconnect the harness connector from the sensor and then use the DVOM set at ohms to test for continuity between the ground and power wires. There should be resistance between the two wires.
Testing Signal Wire
The signal wire must only be tested during actual fan operation through back probing of the harness connector using DVOM set at volts or with the use of graphic multimeter with positive lead on the signal wire and negative lead to a known ground.
As the speed of the fan increases, the voltage must also increase. Thus, it’s good to monitor the fan speed using an advanced scan tool to verify if the actual fan speed matches the commanded fan speed. If the cooling fan speed sensor fails, then it must be replaced.
How to Fix
Depending on the diagnosis, repairs for this code include:
- Repair or replacement of connector or wirings issues in the fan speed sensor
- Replacement of the fan speed sensor
- Replacement of the cooling fan clutch
- Repair or replacement of short in the fan clutch voltage circuit
- Repair fan speed sensor voltage or circuit problem
As with most codes, it’s imperative to always clear the code from the PCM and retesting the system before moving on to another step of the repair. This will allow you to narrow down and pinpoint exactly what went wrong and ensure you make unnecessary replacements.