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Home >> Chevrolet >> 2003 >> Tracker 4D Utility, 2.5 4, 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Emission Systems & Sub-Systems >> EGR System (2.5L) >> Diagnostic Procedures
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Diagnostic Procedures

NOTE: For circuit identification, see WIRING DIAGRAMS .
  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.5L TRACKER article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Check for DTCs. If DTC P0401, P0402 or P0403 is set, perform diagnostic procedure for DTC P0401, P0402 or P0403. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.5L TRACKER article. If DTC P0401, P0402 or P0403 is not set, go to next step.
  3. Start engine and allow it to reach normal operating temperature. Does engine run rough, or idle is unstable, go to step  10. If engine runs smoothly and idle is stable, turn ignition off and go to next step.
  4. Connect scan tool to Data Link Connector (DLC). Clear DTCs. Start engine and allow it to idle. Using scan tool, gradually command EGR valve OPEN to 100 percent. If engine begins to run rough or stall, system is okay. If engine does not begin to run rough or stall, leave engine running and go to next step.
  5. With a test light connected to ground, backprobe EGR coil control circuits at PCM harness connector C4 terminals No. 4 and 17. See Fig 1. Test light should illuminate on both circuits. Continue to backprobe both EGR control circuits with test light. Using scan tool, set EGR valve OPEN value to 5 percent. Observe test light on each circuit while commanding EGR valve OPEN. Test light should illuminate and then turn off when EGR valve is commanded OPEN. If EGR valve passes both tests, go to next step. If EGR valve does not pass both tests, go to step  7.
  6. Leave engine running. With test light still connected to ground, backprobe EGR coil control circuits at PCM harness connector C4 terminals No. 5 and 16. See Fig 1. Test light should not illuminate on either circuit. Continue to backprobe both EGR control circuits with test light. Using scan tool, set EGR valve OPEN value to 5 percent. Observe test light on each circuit while commanding EGR valve OPEN. Test light should illuminate when EGR valve is commanded OPEN. If EGR valve passes both tests, go to step  8. If EGR valve does not pass both tests, go to next step.
  7. Turn ignition off. Disconnect EGR valve harness connector. Using DVOM, measure resistance of EGR valve coil windings (one at a time) between terminals No. 1 and 2, No. 2 and 3, No. 5 and 6, and No. 4 and 5. See Fig 2. Resistance should be 20-24 ohms at 68°F (20°C). Also, measure resistance between EGR valve assembly body and terminals No. 2 and 5. Resistance should be infinite. If EGR valve passes all resistance tests, go to step  9. If EGR valve does not pass all resistance tests, go to step  15.
  8. Remove EGR valve. Inspect EGR passages for any obstruction or blockage and EGR valve for physical damage or carbon deposits. Repair as necessary. After repairs, go to step  18. If EGR valve and passages are okay, go to step  15.
  9. Disconnect EGR valve harness connector. Turn ignition on with engine off. Using a test light connected to ground, probe power circuits at EGR valve harness connector terminals No. 2 and 5. If test light illuminates on both circuits, go to step  14. If test light does not illuminate on both circuits, go to step  13.
  10. With engine running, disconnect EGR valve harness connector. If engine performance improves when EGR valve is disconnected, go to step  12. If engine performance does not improve when EGR valve is disconnected, go to next step.
  11. Remove EGR valve. Check for binding or incorrectly seated EGR valve plunger or leaking EGR valve or gasket. Repair or replace as necessary. After repairs, go to step  18.
  12. Check EGR coil control circuits for an open or short to ground. Repair as necessary. After repairs, go to step  18. If EGR coil control circuits are okay, go to step  16.
  13. Repair ignition voltage supply from main relay to EGR valve harness connector. After repairs, go to step  18.
  14. Check for an open or a short in EGR valve coil control circuits that did not illuminate on and off in step  5 or  6. Repair as necessary. After repairs, go to step  18. If EGR valve coil control circuits are okay, go to step  16.
  15. Replace EGR valve. After repairs, go to step  18.
  16. Check for poor electrical connections at EGR valve and PCM. Repair as necessary. After repairs, go to step  18. If electrical connections are okay, go to next step.
  17. Replace PCM. See REMOVAL & INSTALLATION - TRACKER article. After repairs, go to next step.
  18. Operate vehicle under conditions which original symptom was noted. If system operates properly, system is okay. If system does not operate properly, see DIAGNOSTIC AIDS .
Fig 1: Identifying PCM Harness Connector C4 Terminal (Back View)
G00117322Courtesy of GENERAL MOTORS CORP.
Fig 2: Identifying EGR Valve Harness Connector Terminals (2.5L)
G00117326Courtesy of GENERAL MOTORS CORP.
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