GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Yukon XL Denali 🢒 Engine 🢒 Engine Exhaust 🢒 Restricted Exhaust

Test Description

Caution: While engine is operating, the exhaust system will become extremely hot. To prevent burns avoid contacting a hot exhaust system.

The numbers below refer to the step numbers in 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 heater oxygen sensor (HO2S) may set a diagnostic trouble code (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.

    3.

  3. Confirming that the condition has been fixed is essential. If the symptom still exists and the vehicle has a dual exhaust system, proceed to Step 2 and repeat the diagnostic procedure on the opposite exhaust pipe.

Step

Action

Value(s)

Yes

No

1

Did you verify the customers 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

  1. Remove the heated oxygen sensor (HO2S) that is in front of and closest to the catalytic converter. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 .
  2. Install the J 35314-A Exhaust Back Pressure Gage in place of the HO2S sensor.
  3. Start the engine.
  4. Increase and monitor the engine speed at 2,000 RPM.
  5. Observe the exhaust system back pressure reading on the gage.

Does the reading exceed the specified value?

3.4 kPa (0.5 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. Re-install the HO2S sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 .
  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 .
  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 2,000 RPM.
  8. Observe the exhaust system back pressure reading on the gage.

Does the reading exceed the specified value?

3.4 kPa (0.5 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 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. Re-install the HO2S sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 .
  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