GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Generic 🢒 2005 🢒 Unit Repair 🢒 Engine 🢒 Engine Controls - 3.5L (LX9) 🢒 Restricted Exhaust

Test Description

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

  1. The exhaust system has very low back pressure under normal conditions. If the exhaust system is restricted, a significant increase in the exhaust pressure is noticed on the J 35314-A Exhaust Back Pressure Gage.

    Removing the heated oxygen sensor (HO2S) may set a DTC. When finishing this diagnostic table, be sure to clear all codes.

  2. This step will isolate the catalytic converter from the remainder of the exhaust system.

Step

Action

Values

Yes

No

1

Did you verify the customer complaint?

--

Go to Step 2

--

2

Did you review the exhaust symptoms diagnostic information and perform the necessary inspections?

--

Go to Step 3

Go to Symptoms - Engine Exhaust

3

    Caution: Refer to Hot Exhaust System Caution in the Preface section.

  1. Remove the pre-catalyst heated oxygen sensor (HO2S). Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 in Engine Controls - 3.5L (LX9).
  2. Install the J 35314-A Exhaust Back Pressure Gage in place of the HO2S sensor.
  3. Start and run the vehicle.
  4. Increase and monitor the engine speed at 2,500 RPM.
  5. Observe the exhaust system back pressure reading on the gage.

Does the reading exceed the specified value?

9 kPa (1.25 psi)

Go to Step 4

Go to Step 7

4
  1. Turn the engine OFF and place the ignition in the LOCK position.
  2. Remove the J 35314-A .
  3. Install the pre-catalyst HO2S sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 in Engine Controls - 3.5L (LX9).
  4. Remove the post-catalyst HO2S sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 in Engine Controls - 3.5L (LX9).
  5. Install the J 35314-A in place of the post HO2S sensor.
  6. Start the engine.
  7. Increase and monitor the engine speed at 2,500 RPM.
  8. Observe the exhaust system back pressure reading on the gage.

Does the reading exceed the specified value?

9 kPa (1.25 psi)

Go to Step 5

Go to Step 6

5

Inspect the exhaust system for the following conditions:

    • Damage in the exhaust pipe
    • Debris in the exhaust pipe
    • Muffler or resonator internal failure
    • Two-layer exhaust pipe separation

Did you find and correct the condition?

--

Go to Step 7

--

6

Replace the catalytic converter. Refer to Catalytic Converter Replacement .

Did you find and correct the condition?

--

Go to Step 7

--

7

  1. Remove the J 35314-A .
  2. Install the post-catalyst HO2S sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 in Engine Controls - 3.5L (LX9).
  3. Clear any codes.
  4. Road test the vehicle in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2