DL34 - Check Signal at the PFE/DPFE Inlet Hose(s)

- Key "OFF".

- Disconnect and inspect the Pressure Feedback EGR (PFE) / Differential Pressure Feedback EGR (DPFE) inlet hose(s) for kinks, blockages, etc. Service as necessary and reconnect after inspection.

- Install a tachometer, Rotunda 059-00010 or equivalent.

- Disconnect the Idle Air Control (IAC) solenoid electrical connector.

- Remove and plug the vacuum supply hose from the EGR valve nipple.

- Start engine, idle with transmission in neutral, and observe idle speed. If necessary, adjust idle speed.

NOTE: If the engine will not idle with IAC solenoid disconnected, provide an air bypass to the engine by slightly opening the throttle plate or by creating an intake vacuum leak. Do not exceed a typical idle rpm.

- Slowly apply 5-10 inches of vacuum to the EGR valve nipple using a hand vacuum pump, Rotunda 021-00014 or equivalent.

- Does idle speed drop more than 100 rpm with vacuum applied and return to normal (within 25 rpm) after the vacuum is removed?

Yes -- Remove vacuum gauge. Rerun quick test if the inlet hose(s) needed service. Quick Test Appendix (Detailed Testing Instructions)

If service was not needed, then Go to DL35. DL35 - Attempt to Generate KOEO Code 337

No -- Remove and Inspect the EGR valve for signs of contamination, unusual wear, carbon deposits, grinding, and other damage. Exercise the EGR valve with a hand vacuum pump and verify that it opens and holds vacuum. If EGR valve is OK, look for an obstructed EGR passage in the intake manifold. Service as necessary (use Rotunda 021-80056 EGR valve cleaner if needed). Rerun quick test. Quick Test Appendix (Detailed Testing Instructions)