Diagnostic Aids

Perform this test when instructed by QUICK TEST. To prevent replacement of good components, be aware the following non-EEC related areas may be at fault:

• Damaged vacuum hoses.
• Damaged EGR Pressure Transducer (EPT).
• EGR valve.

This test is only intended to diagnose:

• EGR Vacuum Regulator (EVR) solenoid.
• PCM.
• Wiring harness circuits (EVR and VPWR).

EVR solenoid regulates vacuum to EGR valve by way of EVT. When energized, EVR opens a port between manifold vacuum and EGR valve. When not energized, EVR closes port to EGR and vacuum is vented to atmosphere.

1. 1) Code 558
   
   Code 558 indicates failure in EVR solenoid circuit. Possible causes for this fault are:
   • Faulty EVR solenoid.
   • Faulty vacuum hoses.
   • Open or ground circuit in wiring harness.
   • Faulty Powertrain Control Module (PCM).

   Turn ignition off. Remove scan tester (if applicable). Disconnect cruise control servo wiring harness connector. Connect DVOM negative lead to STO terminal at Data Link Connector (DLC). Connect positive lead to positive battery terminal. Install a jumper wire between STI terminal and SIG RTN terminal at DLC. See Figure. Perform KOEO SELF-TEST until continuous memory test is complete. DVOM will read less than one volt when test is complete to indicate PCM has entered OUTPUT STATE CHECK. Depress and release throttle. If voltage does not increase, fully apply throttle and release. If STO voltage remains low, go to CIRCUIT TEST QC . If voltage increases, remain in OUTPUT STATE CHECK and go to next step.

2. 2) Check EVR Solenoid Electrical
   
   Turn ignition off. Remove EVR solenoid wiring harness connector. Connect DVOM positive lead to VPWR terminal and negative test lead to EVR terminal at EVR solenoid wiring harness connector. Depress and release throttle 3-5 times to cycle solenoid output. If EVR solenoid voltage output change is 0.5 volt or more, go to next step. If EVR solenoid voltage output change is less than 0.5 volt, go to step 5).
3. 3) Check EVR Solenoid Vacuum
   
   Turn ignition on. Disconnect EVR solenoid vacuum hoses. Install vacuum pump on EVR solenoid vacuum port. Install vacuum gauge on solenoid output port. Apply 6 in. Hg, and hold. Depress and release throttle 3-5 times to cycle solenoid output. Turn ignition off. If vacuum gauge shows vacuum cycling at output port, go to next step. If vacuum gauge does not show vacuum cycling at output port, replace EVR solenoid and repeat QUICK TEST.
4. 4) Check EVR Vacuum Hoses
   
   Remove jumper wire, vacuum pump and gauge. Remove vacuum hoses individually. Plug one end of hose. Connect vacuum pump at opposite end. Apply vacuum and observe gauge. If vacuum is not held, replace hose and repeat QUICK TEST . If vacuum is held, ensure vacuum port between EPT and EGR is not restricted. If vacuum port is clear, go to next step.
5. 5) Check EVR Solenoid VPWR
   
   Turn ignition off. Disconnect EVR solenoid wiring harness connector. Turn ignition on. Measure voltage between VPWR terminal at wiring harness connector and negative battery terminal. If voltage is 10.5 volts or more, go to next step. If voltage is less than 10.5 volts, repair open VPWR circuit and repeat QUICK TEST.
6. 6) Check EVR Solenoid Circuit Continuity
   
   Turn ignition off. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between EVR terminal at EVR solenoid wiring harness connector and test pin No. 31. If reading is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST.
7. 7) Check EVR Solenoid Circuit For Short
   
   Turn ignition off. Leave EVR solenoid disconnected. Measure resistance between test pin No. 31 and test pins No. 37 and 57 at breakout box. Measure resistance between test pin No. 31 and test pins No. 40, 46 and 60 at breakout box. If each resistance is 10,000 ohms or more, replace PCM and repeat QUICK TEST. If reading is less than 10,000 ohms, repair short circuit and repeat QUICK TEST.