GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0526: Cooling Fan Speed Sensor Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Relay Ground

--

P0483, P0493

--

--

Relay Voltage Supply

P0480, P0483, P0493, P1482

P0480, P0483, P0493, P1482

--

--

Relay Control

P0480, P1482

P0480, P1482

P0480, P1482

--

Speed Sensor Low Reference

--

P0483, P0493, P0526

--

--

Speed Sensor 5-Volt Reference

--

P0526

--

--

Speed Sensor Signal

P0526

P0526

P0526

--

Clutch Ground

--

P0483, P0493

--

--

Clutch Voltage Supply

P0483, P0493

P0483, P0493

P0483, P0493, P0495

--

Circuit/System Description

The control module uses the cooling fan speed signal in order to determine the actual fan speed in relation to the desired fan speed. The control module uses the cooling fan speed signal in order to reduce the cooling fan noise and in order to maintain the powertrain cooling requirements. The control module supplies power and ground to the clutch hall effect sensor of the cooling fan clutch. The hall effect sensor returns a signal pulse through the speed signal circuit in response to the reluctor track, which is located inside the fan clutch. If during operation, the control module detects a loss of the cooling fan speed signal, DTC P0526 will set.

Conditions for Running the DTC

    • The engine is running.
    • System voltage is greater than 8.5 volts.

Conditions for Setting the DTC

    • The powertrain control module (PCM) has detected a loss of cooling fan speed signal.
    • The above condition is present for at least 11 seconds.

Action Taken When the DTC Sets

DTC P0526 is a Type B DTC.

Conditions for Clearing the DTC

DTC P0526 is a Type B DTC.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

    •  Cooling System Connector End Views
    •  Powertrain Control Module Connector End Views for 4.2L
    •  Engine Control Module Connector End Views for 5.3L
    •  Engine Control Module Connector End Views for 6.0L

Description and Operation

Cooling Fan Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs
    •  Electrical Center Identification Views

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification

  1. Idle the engine.
  2. Command the cooling fan clutch to 10 percent.
  3. Operate the engine at 2,000 RPM for 2 minutes. The fan should be quiet to indicate the clutch is disengaged.
  4. Command the cooling fan clutch to 80 percent.
  5. Operate the engine at 2,000 RPM for 2 minutes. The fan should be loud to indicate the clutch is engaged.
  6. Operate the vehicle within the Conditions for Running and setting the DTC, and verify the DTC does not set.
  7. If the DTC sets, proceed with Circuit/System Testing.

Circuit/System Testing

Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

  1. Ignition OFF, disconnect the fan clutch at the shroud.
  2. Measure between the low reference circuit terminal A and ground for less than 3 ohms.
  3. If more than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the control module.
  4. Ignition ON, measure between the 5-volt reference circuit terminal E and the low reference circuit terminal C for 4.8-5.2 volts.
  5. If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the control module.
    If more than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the control module.
  6. Install jumper wires in the 5-volt reference and low reference circuits between the harness and pigtail connectors at the shroud.
  7. • 5-volt reference circuit--terminals E
    • Low reference circuit--terminals C
  8. Measure DC voltage between the signal circuit terminal D at the sensor pigtail connector and the 5-volt reference circuit jumper wire terminal.
  9. Ignition ON, rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts.
  10. If the voltage does not toggle correctly, test the 3 circuits in the pigtail harness for a short to ground, a short to voltage, or an open/high resistance. If the circuits test normal, replace the clutch.
  11. Leave the jumpers from the previous step in place. Measure voltage between the signal circuit terminals D at the harness and pigtail connectors at the shroud.
  12. Rotate the fan by hand. The voltage should toggle between approximately 5 volts and 0 volts.
  13. If the voltage does not toggle correctly, test the signal circuit for a short to ground or a short to voltage. If the circuit tests normal, replace the control module.
  14. If all circuits and the speed sensor test normal, replace the engine control module (ECM).

Component Testing

Relay Test

  1. Connect the relay ground terminal to ground and the voltage supply terminal to appropriately fused power to energize the relay.
  2. Test for less than 1 volt between the load voltage supply terminal and ground.
  3. Connect the relay control circuit terminal to ground.
  4. Test for B+ between the load voltage supply terminal and ground.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Fan Clutch Replacement
    •  Cooling Fan and Shroud Replacement
    •  Cooling Fan Relay Replacement
    •  Control Module References for replacement, setup, and programming