DN24 - Fault Isolation Check

The fault has been isolated to the EGR valve or EGR Valve Position (EVP) sensor. Due to the nature of this particular fault, the EGR valve is suspect because of its vulnerability to contamination and carbon build-up from the exhaust flow. If the engine runs rough at idle, this is a good indication that the EGR valve is not fully seated rather than a worn or damaged sensor.

- Remove the EGR valve and EVP sensor.

- Inspect both components for contamination, unusual wear, carbon deposits, binding and other damage. Service as necessary. (Use Rotunda EGR Valve Cleaner 021-80056 or equivalent if needed.)

- Reinstall EGR valve and EVP assembly and run Key On Engine Off (KOEO) and Key On Engine Running (KOER) Self-Test. Quick Test Appendix (Detailed Testing Instructions)

- Is Diagnostic Trouble Code (DTC) 334 still present?

Yes -- Replace EGR valve. Remove breakout box. Rerun quick test. Quick Test Appendix (Detailed Testing Instructions)

If DTC is still present, replace EVP sensor.

No -- The original DTC 334 was the result of EGR valve contamination, binding or a worn or damaged EVP sensor. Testing complete.