GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Controls - 6.6L (LLY) 🢒 Restricted Exhaust

Diagnostic Aids

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

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. 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 diagnostic procedure on the opposite exhaust pipe.

Restricted Exhaust

Step

Action

Value(s)

Yes

No

1

Did you verify the customers concern?

--

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 HO2S that is in front of and closest to the catalytic converter. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 .
  2. Install the J 35314-A in place of the HO2S sensor.
  3. Start the engine.
  4. Increase and monitor the engine speed at 2000 RPM.
  5. Observe the exhaust system back pressure reading on the gage.

Does the reading exceed the specified value?

14 kPa (2 psi)

Go to Step 5

Go to Step 8

5

  1. Turn the engine off and place the ignition in the lock position.
  2. Remove the muffler. Refer to Muffler Replacement
  3. Start the engine.
  4. Increase and monitor the engine speed at 2000 RPM.
  5. Observe the exhaust system back pressure reading on the gage.

Does the reading exceed the specified value?

14 kPa (2 psi)

Go to Step 6

Go to Step 7

6

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 8

--

7

Replace the catalytic converter. Refer to Catalytic Converter Replacement .

Did you find and correct the condition?

--

Go to Step 8

--

8

  1. Remove the J 35314-A .
  2. Reinstall the HO2S sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 .
  3. Reinstall the muffler. Refer to Muffler Replacement .
  4. Clear any codes.
  5. Road test the vehicle in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2