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Home >> Cadillac >> 1998 >> Eldorado Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0401 - EGR System Malfunction >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK , then go to next step.
  2. If fuel trim DTC(s) P0170, P0171, P0172, P0173, P0174 or P0175 are present, diagnose affected DTC(s) first. If these DTCs are not present, go to next step.
  3. Ignition on, with engine off. Check MAP sensor parameter on scan tool. If value is greater than 75 kPa (95 kPa at sea level), go to next step. If value is not greater than 75 kPa (95 kPa at sea level), go to step 9).
  4. Unplug MAP sensor vacuum hose. Connect a hand-held vacuum pump to MAP sensor. Apply 20 in. Hg to sensor. Each one in. of vacuum should result in a 3-4 kPa drop in MAP sensor reading. Change should be smooth. If a skip or jump occurs during application of vacuum, go to step 9). If change in reading is smooth, go to next step.
  5. With 20 in. Hg applied to sensor, if MAP reading is 34 kPa or less, go to next step. If MAP reading is not 34 kPa or less, go to step 9).
  6. Remove vacuum source from MAP sensor. If MAP sensor parameter returns to original reading, go to next step. If MAP parameter does not return to original reading, go to step 9).
  7. Reconnect MAP sensor vacuum hose. Start and idle engine. While monitoring MAP sensor value, command EGR from 0-70 percent in 10 percent increments. MAP sensor value should increase by about 4 kPa for each 10 percent increment. If MAP value does not increase accordingly and engine does not stall, go to next step. If MAP value increases accordingly or engine stalls, check EGR system for intermittent restrictions, blockages and/or leaks. If no fault is found, problem is intermittent.
  8. Check EGR valve and all engine passages for restrictions and/or blockages. Repair as necessary. If no repairs are required, go to step 10).
  9. Replace MAP sensor.
  10. Replace EGR valve and verify if problem is no longer present.
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