Code P0526 and running rough

Hi,

The code you indicated is related to the cooling fan on both the GM and Isuzu. I'm not sure how that would cause it to run rough. However, I have a few questions. First, does the engine light only come on when it is running rough? Is there ever any engine temperature concerns?

Here is the description of the code on a GM vehicle. The attached two pics are a flow chart explaining how to locate and repair the issue. The same information is on the Isuzu page.

2004 Chevy Truck TrailBlazer 2WD L6-4.2L VIN S
P0526
Vehicle ALL Diagnostic Trouble Codes ( DTC ) Testing and Inspection P Code Charts P0526
P0526
DTC P0526

Circuit Description
The Powertrain Control Module (PCM) uses the cooling fan speed signal in order to determine the actual fan speed in relation to the desired fan speed. The PCM uses the cooling fan speed signal in order to reduce the cooling fan noise and in order to maintain the powertrain cooling requirements. The PCM 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 PCM 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 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
The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
The PCM will store the condition as Freeze Frame/Failure Records data.
The PCM commands the cooling fan to 100%.

Conditions for Clearing the MIL/DTC
The PCM turns OFF the Malfunction Indicator Lamp (MIL) after the third consecutive trip that the diagnostic test has run and passed.
Clear the DTC by using the Clear DTC Information function of the scan tool.

Diagnostic Aids
An inline connector could cause an intermittent DTC. Ensure to test for poor connections and pin retention at all inline connectors. Refer to system schematics for connectors and locations.
If the condition is not present, refer to Testing for Intermittent and Poor Connections.
Disconnect the harness connector of the cooling fan clutch from the shroud. Inspect the exposed wires between the harness connector and the tubing.
Inspect the cooling fan clutch harness in order to ensure that the clutch supply voltage circuit is not shorted to the following circuits:
- The 5-volt reference circuit.
- The cooling fan speed signal circuit.
- The low reference circuit.
DTC P0526 will set if the engine is started without the drive belt ON.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. Tests that the PCM receives a cooling fan speed signal through the cooling fan speed signal circuit. If answer to question is Yes, ensure to refer to all Diagnostic Aids.
3. Tests for the proper operation of the cooling fan clutch hall effect sensor. The voltage should fluctuate between 0 and 5 volts. If the voltage stays at 0 volts, the signal circuit is shorted to ground.
4. Tests for the proper operation of the 5-volt reference circuit and of the low reference circuit of the cooling fan clutch.

Let me know.

Joe

Yes it could be the PCM (not BCM). However, it could be a corroded connection, broken wire, and so on. If could also be the reluctor ring in the clutch assembly or the hall affect sensor has failed. If you have access to a scanner that can identify freeze frame data, check to see when the failure occurred, and where the problem seems to originate.

If that isn't an option, I feel I would focus on the fan assembly itself. Not saying the PCM can be an issue, but based on the code, I don't feel it is. Instead, I feel the sensor is a more likely suspect or a bad connection. In reality, the PCM seems to be functioning properly by requesting 100% from the fan.

Check the sensor and connections first. If you look through my last post, it will describe how to do it. Please feel free to ask me questions if you run into trouble.

Take care and let me know what you find.

Joe