Diagnostic Aids

Perform this test when instructed by QUICK TEST or other test. This test is only intended to diagnose the following:

• EGR valve.
• EGR temperature sensor.
• EGR/EVAP purge control solenoid.
• Harness circuits; EGRT, EGR/EVAP and SIG RTN.
• Vacuum hoses.
• Faulty PCM.
  CIRCUIT PIN IDENTIFICATION
  
  

  Circuit	Breakout Box Pin No.	PCM Pin No.	Wire Color
  EGR/EVAP	70	73	Gray
  EGR TEMP	59	62	(1) White/Purple
  SIG RTN	45	50	Black/Yellow
  (1) White/Red wire at EGR temperature sensor connector.

  Fig 1: EGR System Schematic

  
  TEST DIRECTORY
  
  

  DTC	Action
  P0400	Go To Step 1)
  P1400	Go To Step 20)
  P1401	Go To Step 30)
  P0402	Go To Step 35)

1. 1) Inspect EGR System
   
   DTC P0400 indicates EGR flow malfunction. Possible causes are as follows:
   • Open or shorted EGR circuit.
   • EGR valve malfunction.
   • EGR Backpressure (EGR BPT) malfunction.
   • EGR passage obstructed or leaking.
   • EGR/EVAP control solenoid malfunction.
   • EGR temperature sensor malfunction.

   Check all vacuum hoses for damage. Check EGR/EVAP control solenoid and EGR temperature sensor wiring for corrosion or damage. Repair as necessary. If vacuum hoses and wiring is okay, go to next step.

2. 2) Check Vacuum To EGR Valve
   
   Start and run engine to operating temperature. Disconnect vacuum hose at EGR valve. Check vacuum at disconnected hose while running engine at 2000-4000 RPM. If vacuum is present at 2000-4000 RPM, go to step 8). If vacuum is not present, go to next step.
   NOTE: On vehicles with California emissions, EGR and EVAP systems use separate solenoids.
3. 3) Check EGR/EVAP Control Solenoid Operation
   
   Start and run engine to operating temperature. Turn ignition off. Connect NGS scan tool to OBD-II DLC. Turn ignition on (engine off). Access simulation test and select EGRC PID. If EGR/EVAP solenoid clicks when EGRC PID is turned off, go to step 5). If solenoid does not click, go to step 10).
4. 4) Check EGR/EVAP Control Solenoid Operation
   
   Start and run engine to operating temperature. Turn ignition off. Turn ignition on (engine off). Disconnect EGR/EVAP solenoid harness connector. If EGR/EVAP solenoid clicks when disconnected, go to next step. If solenoid does not click, go to step 10).
5. 5) Check EVAP Canister For Leaks
   
   Turn ignition off. Disconnect vacuum hose from uppermost port on EVAP canister. Connect a length of hose to disconnected port on EVAP canister. Gently blow through hose into EVAP canister. If EVAP canister holds pressure, go to next step. If EVAP canister leaks, replace EVAP canister.
6. 6) Check EGR/EVAP Purge Control Solenoid
   
   Turn ignition off. Disconnect vacuum hoses and harness connector from EGR/EVAP purge control solenoid. Ensure air can pass between ports "A" and "C". See Fig 2. Connect battery voltage to EGR/EVAP purge control solenoid (ensure polarity is correct). Air should be able to pass between ports "A" and "B". If EGR/EVAP purge control solenoid functions properly, go to next step. If purge control solenoid does not function properly, replace EGR/EVAP purge control solenoid.
   Fig 2: Testing EGR/EVAP Purge Control Solenoid

   
7. 7) Check EGR BPT (No Exhaust Pressure)
   
   Turn ignition off. Disconnect vacuum hoes from Backpressure Transducer (BPT). Plug one port on top BPT and connect a vacuum pump to other port on top of valve. Apply vacuum to BPT valve. If vacuum does not hold, go to next step. If vacuum holds, replace BPT valve. Repeat QUICK TEST .
8. 8) Check EGR BPT
   
   Turn ignition off. Disconnect vacuum hoses from EGR BPT. Blow into exhaust pressure port and maintain about 0.2 psi (1 kPa). Plug one port on top of BPT and apply vacuum to other port. If vacuum does not hold, replace BPT valve. If vacuum holds, go to next step.
9. 9) Check EGR Valve
   
   Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR vacuum port. Apply vacuum to EGR valve while feeling for movement of EGR valve diaphragm. If diaphragm does not move, replace EGR valve and repeat QUICK TEST . If EGR valve diaphragm moves without sticking when vacuum is applied, go to step 30).
   NOTE: On vehicles with California emissions, EGR and EVAP systems use separate solenoids.
10. 10) Check Power To EGR/EVAP Purge Solenoid
    
    Turn ignition off. Disconnect EGR/EVAP purge control solenoid harness connector. Turn ignition on. Measure voltage between White/Red wire at EGR/EVAP purge control solenoid harness connector and ground. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open VPWR (White/Red) wire. Restore all electrical connections and repeat QUICK TEST .
11. 11) Check EGR/EVAP Purge Control Solenoid
    
    Turn ignition off. Disconnect vacuum hoses and harness connector from EGR/EVAP purge control solenoid. Ensure air can pass between port "A" and "C". See Fig 2. Connect battery voltage to EGR/EVAP purge control solenoid (ensure polarity is correct). Air should be able to pass between port "A" and "B". If EGR/purge control solenoid functions properly, go to next step. If purge control solenoid does not function properly, replace EGR/EVAP purge control solenoid.
12. 12) Check EGRC Wire
    
    Turn ignition off. Disconnect PCM harness connector, check for damaged or pushed out pins. Repair as necessary. Install breakout box (leave PCM disconnected). Disconnect EGR/EVAP purge control solenoid harness connector. Measure resistance of Gray wire between EGR/EVAP purge control solenoid harness connector and breakout box test pin No. 70. Resistance should be less than 5 ohms. Measure resistance between ground and breakout box test pin No. 70. Resistance should be greater than 10 k/ohms. If both resistance measurements are as specified, replace PCM. Restore all electrical connections and repeat QUICK TEST . If either resistance measurement is not as specified, repair open or shorted circuit. Restore all electrical connections and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 20). No test procedures have been omitted.
13. 20) Check EGR/EVAP Purge Signal
    
    Turn ignition off. Connect NGS scan tool to OBD-II DLC. Turn ignition on. Select ACTIVE COMMAND MODES. Access EGRC (control) PID. Turn EGRC ON and OFF. If EGR/EVAP purge control solenoid clicks, go to step 24). If EGR/EVAP purge control solenoid does click, go to next step.
14. 21) Check Power To EGR/EVAP Purge Solenoid
    
    Turn ignition off. Disconnect EGR/EVAP purge control solenoid harness connector. Turn ignition on. Measure voltage of White/Red wire at EGR/EVAP purge control solenoid harness connector. If voltage is greater than 10.5 volts, go to next step. If voltage is less than 10.5 volts, repair open VPWR (White/Red) wire. Restore all electrical connections and repeat QUICK TEST .
    NOTE: On vehicles with California emissions, EGR and EVAP systems use separate solenoids.
15. 22) Check EGR/EVAP Purge Control Solenoid
    
    Turn ignition off. Disconnect vacuum hoses and harness connector from EGR/EVAP purge control solenoid. Ensure air can pass between port "A" and "C". See Fig 2. Connect battery voltage to EGR/EVAP purge control solenoid (ensure polarity is correct). Air should be able to pass between port "A" and "B". If EGR/EVAP purge control solenoid functions properly, go to next step. If purge control solenoid does not function properly, replace EGR/EVAP purge control solenoid.
16. 23) Check EGRC Wire
    
    Turn ignition off. Disconnect PCM harness connector, check for damaged or pushed out pins. Repair as necessary. Install breakout box (leave PCM disconnected). Disconnect EGR/EVAP purge control solenoid harness connector. Measure resistance of Gray wire between EGR/EVAP purge control solenoid harness connector and breakout box test pin No. 70. Resistance should be less than 5 ohms. Measure resistance between ground and breakout box test pin No. 70. Resistance should be greater than 10 k/ohms. If both resistance measurements are as specified, go to step 30). If either resistance measurement is not as specified, repair open or shorted circuit. Restore all electrical connections and repeat QUICK TEST .
17. 24) Check EGR Valve
    
    Disconnect vacuum hose from EGR valve. Connect a vacuum pump to EGR vacuum port. Apply vacuum to EGR valve while feeling for movement of EGR valve diaphragm. If diaphragm does not move, replace EGR valve and repeat QUICK TEST . If EGR valve diaphragm moves without sticking when vacuum is applied, go to step 30).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 24) to step 30). No test procedures have been omitted.
18. 30) Check EGR Temperature Sensor Resistance
    
    Warm engine to operating temperature. Turn ignition off. Disconnect EGR temperature sensor harness connector. Using a digital thermometer, check temperature at EGR temperature sensor. Measure resistance between the terminals of EGR temperature sensor as engine cools. Compare resistance to EGR TEMPERATURE SENSOR RESISTANCE table. If sensor is within specified resistance, go to next step. If sensor resistance is not within specification, replace EGR temperature sensor. Repeat QUICK TEST .
    EGR TEMPERATURE SENSOR RESISTANCE
    
    

    Coolant Temperature °F (°C)	EGR Temperature Sensor Resistance (M/ohms)
    68-120 (20-49)	2.25-2.55
    130-148 (55-65)	1.75-2.25
    150-165 (66-74)	1.40-1.75
    168-190 (76-88)	1.00-1.40

19. 31) Check EGR Temperature Sensor
    
    Start engine and run to operating temperature. Install NGS scan tool to OBD-II data link connector. Access EGRT PID. Apply vacuum to EGR valve with engine running at 2000 RPM. If EGRT PID voltage is greater than one volt with EGR valve closed and less than one volt with EGR valve open, EGR temperature sensor and circuit is okay, fault may be intermittent, go to CIRCUIT TEST Z  for intermittent diagnostic procedure. If voltage is not as specified, replace EGR temperature sensor.
20. 32) Check EGRT Wire
    
    Turn ignition off. Disconnect PCM harness connector, check for damaged or pushed out pins. Repair as necessary. Install breakout box (leave PCM disconnected). Disconnect EGR temperature sensor harness connector. Measure resistance of White/Red wire between EGR temperature sensor harness connector and breakout box test pin No. 59 (EGRT). Resistance should be less than 5 ohms. Measure resistance between ground and breakout box test pin No. 59 (EGRT). Resistance should be greater than 10 k/ohms. If both resistance measurements are as specified, go to next step. If either resistance measurement is not as specified, repair open or shorted circuit. Restore all electrical connections and repeat QUICK TEST .
21. 33) Check SIG RTN Wire
    
    Turn ignition off. Install breakout box (leave PCM disconnected). Disconnect EGR temperature sensor harness connector. Measure resistance of the Black/Yellow wire between EGR temperature sensor harness connector and breakout box test pin No. 45 (SIG RTN). If resistance is less than 5 ohms, Replace PCM. Restore all electrical connections and repeat QUICK TEST . If resistance is greater than 5 ohms, repair open Black/Yellow wire. Restore all electrical connections and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 33) to step 35). No test procedures have been omitted.