GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2002 🢒 Bravada - 2WD 🢒 Engine 🢒 Engine Controls - 4.2L 🢒 Restricted Exhaust

Tools Required

J 35314-A Exhaust Back Pressure Gage

Diagnostic Aids

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

For dual exhaust systems a quick check of exhaust flow will help determine which side of the exhaust system is restricted. The side that has less exhaust flow is the side that will be suspect, and diagnosis should begin there.

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 .

    Removing the AIR check valve or HO2S sensor may set a DTC. When finishing this diagnostic table, be sure to clear all codes.

  2. If high back pressure is not found at idle, increasing the engine speed may help find a restriction.

    Perform operational check before returning vehicle to customer.

    3.

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

    4.

  4. 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 diagnostic procedure on the opposite exhaust pipe.

Restricted Exhaust

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

Is the system equipped with dual exhaust?

--

Go to Diagnostic Aids

Go to Step 4

4

  1. Remove the AIR check valve or the HO2S that is in front of and closest to the catalytic converter.
  2. Install the J 35314-A in place of the AIR check valve or HO2S sensor.
  3. Start and run the vehicle.
  4. With the engine idling at normal operating temperature, record the exhaust system back pressure reading on the gauge.

Does the reading exceed the specified value?

8.6 kPa (1.25 psi)

Go to Step 6

Go to Step 5

5

  1. With the J 35314-A still installed increase and monitor engine speed to 2000 RPM.
  2. Observe the exhaust system back pressure reading on the gage.

Does the reading exceed the specified value?

20.7 kPa (3 psi)

Go to Step 6

Go to Step 9

6

  1. Turn the engine off and place the ignition in the lock position.
  2. Remove the J 35314-A .
  3. Re-install the AIR check valve/HO2S sensor.
  4. Remove the post-catalyst HO2S sensor.
  5. Install the J 35314-A in place of the post HO2S sensor.
  6. Start and idle the engine and monitor the engine speed to 2000 RPM.
  7. Observe the exhaust system back pressure reading on the gauge.

Does the reading exceed the specified value?

20.7 kPa (3 psi)

Go to Step 7

Go to Step 8

7

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  9

--

8

Replace the catalytic converter. Refer to Catalytic Converter Replacement .

Did you find and correct the condition?

--

Go to Step 9

--

9

  1. Remove the J 35314-A and reinstall the AIR check valve or the HO2S sensor.
  2. Clear any codes.
  3. Road test the vehicle in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2