GM Service Manual Online
For 1990-2009 cars only

System Description


Object Number: 12980  Size: SH

Proper diagnosis for a restricted exhaust system is essential before any components are replaced. Using the Restricted Exhaust System Check table should determine if the exhaust system is restricted. The best place for checking the exhaust system is at the O2S 1 location. Once the test is completed, coat threads with anti-seize compound P/N 5613695 or equivalent prior to O2S re-installation.

Test Description

The number(s) below refer(s) to the step number(s) on the Diagnostic Table.

  1. The OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the fault occurred. The scan tool stores this data for later reference.

  2. The exhaust system under normal conditions has very low back pressure. If the exhaust system is restricted, a noticeable increase in exhaust pressure is noticed on the gauge.

  3. If no high back pressure is found at idle, increasing the engine speed to 3000 RPM may find a slight restriction. The added engine speed increases the exhaust flow which will help determine if there is a slight restriction.

Restricted Exhaust System Check

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Carefully remove the O2S 1 from the exhaust manifold.
  2. Install the exhaust back pressure tester J 35314-A in place of the O2S 1.

Is the action complete?

--

Go to Step 3

--

3

  1. Turn ON the ignition leaving the engine running.
  2. With the engine idling in park or neutral, observe the exhaust system back pressure reading on the gauge. The reading should not exceed the specified value.

Does the reading exceed the specified value?

3.4 kPa (0.5 psi)

Go to Step 5

Go to Step 4

4

Increase the engine speed to 3000 RPM and observe the back pressure reading on the gauge. The reading should not exceed the specified value.

Does the reading exceed the specified value?

5 kPa (0.75 psi)

Go to Step 5

Go to Step 7

5

  1. Check the entire exhaust system for a collapsed pipe, heat distress, or possible internal muffler failure.
  2. Replace any malfunctioning component.

Did any component require replacement?

--

Go to Step 7

Go to Step 6

6

Replace the catalytic converter.

Is the action complete?

--

Go to Step 7

--

7

  1. Idle the engine until the normal operating temperature is reached.
  2. Check to see if any DTCs are set.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to the applicable DTC table

System OK