GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 CTS 🢒 Engine 🢒 Engine Exhaust 🢒 Restricted Exhaust

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 Exhaust Back Pressure Gage.

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

    2.

  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.

Step

Action

Value(s)

Yes

No

1

Did you verify the customer complaint?

--

Go to Step 2

--

2

Did you review the exhaust symptom 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 heated oxygen sensor (HO2S) that is in front of the catalytic converter. Refer to the appropriate procedure.
  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 2,500 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 5

Go to Step 8

5

  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 the appropriate procedure.
  4. Remove the post-catalyst HO2S sensor. Refer to the appropriate procedure.
  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 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 - Left Side or Catalytic Converter Replacement - Right Side .

Did you find and correct the condition?

--

Go to Step 8

--

8

  1. Remove the J 35314-A .
  2. Reinstall the applicable HO2S sensor. Refer to the following:
  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