Diagnostic Information/Recommendations for Low Power/Poor Performance or Catalytic Converter Plugging Concerns

Some of the above-listed vehicles may exhibit a low power/poor performance condition. This may or may not illuminate the Check Engine light.

The technician may diagnose a low power/poor performance situation as a plugged catalytic converter and a subsequently plugged EGR valve. Typically, the converter will plug and the resulting excessive back pressure may cause the EGR pintle to stick open. This would illuminate the check engine light and record various EGR fault codes. The actual cause of the catalytic converter plugging may not be readily apparent.

In addition, the excessive heat generated by a plugged converter may damage O2 sensor and knock sensor wiring on the engine due to over temperature. Suspect vehicles may show the effects of excessive underhood temperatures in the area of the exhaust manifolds or in areas where the flow path of heat is being directed.

Diagnostic Recommendations/Instructions

Catalytic converter concerns are not usually primary in nature. Converters are usually affected by an engine condition or malfunction.

The LP4 and L21 engines built prior to 4-13-1999 were built with cast iron exhaust manifolds. These manifolds may be subject to a heat/age deterioration that results in rust formation and scaling internally. The flakes of rust may get blown through the muffler and then plug the converter.

Use the following recommended diagnostic procedure information for repair.

1. Test drive the vehicle in order to verify the condition.
2. Verify that the vehicle is equipped with cast iron manifolds. Cast iron manifolds are magnetic.
3. Test the catalytic converter in order to find out if it is plugged.

3.1.	Install the J 35314-A - Exhaust Back Pressure Gauge in place of the HO2S

3.2.	Run the engine at 2000 RPM

3.3.	Record the back pressure. If the back pressure exceeds 14 kPa (2 psi), replace the catalytic converter. Refer to SI Document ID #727369.

Loose rust particles may fall out of the converter inlet when removed.

4. Verify if any DTC codes are present. If EGR codes are present, then the pintle may be stuck. Test as required.
5. Replace the converter if it is plugged and install cast stainless manifolds. Replace the EGR valve if necessary.
6. Inspect and repair/replace all damaged engine wiring. Install new plastic conduit.
7. Wrap all repaired wiring with heat reflective tape.

Parts are currently available from GMSPO.

Labor operation numbers have been established for this repair. Please use the applicable labor operation number(s) for the repair completed.