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For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2006 🢒 Ascender - 2WD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC P0495

Circuit Description

The cooling fan relay sends a pulse width modulation (PWM) signal (12-14 volts) to the cooling fan by the cooling fan clutch supply voltage circuit. The powertrain control module (PCM) uses the PWM signal, which controls the speed of the cooling fan clutch by controlling the position of the oil control valve inside the clutch. If the cooling fan clutch RPM is to high when the PCM is commanding 0 percent, DTC P0495 will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0495 Cooling Fan Speed High

Conditions for Running the DTC
    • The engine is running.
    • The system voltage is greater than 8.5 volts.
    • The intake air temperature (IAT) is greater than -7°C (19°F).
    • Zero percent duty cycle is commanded, and the engine RPM has been over 1,800 RPM for at least 120 seconds.

Conditions for Setting the DTC

Cooling fan RPM exceeds 1,600 RPM for 81 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates 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 conditions as Freeze Frame/Failure Records data.

Conditions for Clearing the MIL/DTC
    • The PCM turns the MIL OFF after the third consecutive trip that the diagnostic procedure has run and passed.
    • Clear the DTC 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 connector and locations.
    • If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections .
    • If DTCs P0495 and P0113 are set and the weather is cold, the cooling fan code may be false. Clear DTC P0495, and after an IAT repair, check if the DTC will reset .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step ensures that the DTC has failed this ignition cycle. If the scan tool displays Passed, the answer is No.

    2.

  2. The cooling fan noise should increase as the cooling fan clutch engages. It can take up to 2 minutes for full cooling fan clutch engagement. If cooling fan clutch is previously fully engaged, then there will not be a noticeable change in cooling fan noise. Compare noise to a known good vehicle. If fan noise is louder than the known good vehicle, answer Yes.

  3. In the previous step the cooling fan clutch was fully engaged. This step tests to ensure that the cooling fan clutch will disengage. A noticeable noise difference should be heard between a fully engaged cooling fan clutch and a disengaged cooling fan clutch. The cooling fan clutch is completely disengaged when the excessive fan noise is not heard.

    4.

  4. Tests the ability of the PCM to control the cooling fan speed. If answer to question is Yes, refer to all Diagnostic Aids.

    5.

  5. Disconnecting the cooling fan clutch and running the engine ensure that the cooling fan clutch is not engaged. When rotating the cooling fan clutch it should spin freely. If not, the cooling fan clutch will not disengage.

Step

Action

Yes

No

Schematic Reference: Engine Cooling Schematics

Connector End View Reference: Cooling System Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. With a scan tool, observe the Powertrain DTC list.
  2. Start the engine.
  3. Operate the vehicle within the Conditions for Running in the DTC.

Does the scan tool indicate the DTC Failed this ignition cycle?

Go to Step 5

Go to Step 3

3

Important: DTC P1482, for 4.2L (LL8), and P0480, for 5.3L (LM4), will set when the cooling fan relay is disconnected.

  1. Turn OFF the ignition.
  2. Disconnect the cooling fan relay.
  3. Connect a 10-amp fused jumper wire between the cooling fan clutch supply voltage circuit of the cooling fan clutch and the ignition 3 voltage circuit of the cooling fan relay.
  4. Start the engine.
  5. Raise engine speed to 2,000 RPM for 2 minutes.

Does the cooling fan clutch engage?

Go to Step 4

Go to Step 5

4

Important: Continuously excessive fan noise is due to the powertrain control module (PCM) commanding the cooling fan clutch to 100 percent engaged or a mechanical failure. If the fan noise decreases during this step, then this DTC is due to an electrical malfunction. Replacing the cooling fan clutch will not correct the condition.

  1. Turn OFF the ignition.
  2. Remove the 10-amp fused jumper wire.
  3. Install cooling fan relay.
  4. Disconnect the cooling fan clutch connector.
  5. Start the engine.
  6. Raise engine speed to 2,000 RPM for 2 minutes.

Does the cooling fan clutch disengage?

Go to Step 6

Go to Step 10

5

  1. Turn OFF the ignition.
  2. Disconnect the cooling fan clutch connector.
  3. Start the engine.
  4. Run the engine at 2,000 RPM for 2 minutes.
  5. Turn OFF the engine.
  6. Rotate the cooling fan 2 revolutions.

Does the cooling fan rotate freely?

Go to Step 6

Go to Step 12

6

  1. Disconnect the harness connector at the shroud.
  2. Turn ON the ignition.
  3. Connect a test lamp between the cooling fan clutch supply voltage circuit of the cooling fan clutch and ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 10

7

Disconnect the cooling fan relay.

Does the test lamp remain illuminated?

Go to Step 8

Go to Step 9

8

Repair the cooling fan clutch supply voltage circuit of the cooling fan clutch for a short to voltage. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 13

--

9

Inspect for poor connections at the cooling fan relay. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 11

10

Inspect for poor connections at the cooling fan clutch. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs .

Did you find and correct the condition?

Go to Step 13

Go to Step 12

11

Replace the cooling fan relay.

Did you complete the replacement?

Go to Step 13

--

12

Replace the cooling fan clutch. Refer to Fan Clutch Replacement .

Did you complete the replacement?

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running in the DTC.

Does the DTC reset?

Go to Step 2

System OK