Code 12: EGR System
NOTE:
For wiring diagrams, see WIRING DIAGRAMS
article. For vacuum diagrams, see VACUUM DIAGRAMS
article.
- Warm engine to normal operating temperature (cooling fan on). Check harness and connections between EGR control solenoid and ECU. Verify vacuum supply to EGR control solenoid. Disconnect vacuum hose No. 11 from EGR valve. Connect vacuum pump to EGR valve and apply vacuum.
- EGR valve should hold vacuum and engine should stall. If not, replace EGR valve. If EGR held vacuum and engine stalled, turn ignition off. Disconnect vacuum hose No. 5 from "T" connector to control box. Connect vacuum gauge. Restart engine. Manifold vacuum should be present. If not, repair blockage at port or hose.
- If vacuum reading is okay, reconnect hoses. Open emission control box and disconnect vacuum hose No. 11 between air chamber and EGR control solenoid. Connect vacuum gauge. If 8 in. Hg is present, inspect hose routing, replace EGR control solenoid valve or repair short in White wire between ECU terminal A10 and EGR control solenoid valve.
- If 8 in. Hg is not present, disconnect 6-pin connector from emission control box. Connect Black/Yellow wire terminal to battery positive terminal and White wire terminal to negative battery terminal. See Fig 1 . If gauge does not read 8 in. Hg within one second, replace EGR control solenoid valve.
- If gauge reads 8 in. Hg within one second, measure voltage between Black/Yellow (positive) wire terminal and ground. If battery voltage is not present, repair open in Black/Yellow wire between EGR control solenoid valve and fuse No. 9. If battery voltage is present, turn ignition off.
- Connect Test Harness (07GMJ-ML80100 ) to EGR harness. Reconnect vacuum hose No. 11. Turn ignition on. Measure voltage between Red (positive) and Green (negative) wire terminals. If about 5 volts is not present, measure voltage between Red (positive) wire terminal and ground.
- If about 5 volts is present, repair open in Green/White wire between ECU terminal C14 and EGR lift sensor. If 5 volts is not present, repair open in Yellow/White wire between ECU terminal C13 and EGR lift sensor. If wire is okay, substitute a known good ECU. If proper voltage is available, replace original ECU.
- If 5 volts is present in step 6), measure voltage between White (positive) and Green (negative) wire terminals. If about one volt is not present, replace EGR valve. Repair short in White/Green wire between ECU terminal C8 and EGR lift sensor.
- If about one volt is present, turn ignition off. Connect ECU test harness to ECU. See Figure . Turn ignition on. Measure voltage between terminals C8 and C14. If about one volt is not present, repair open in White/Green wire between C8 and EGR lift sensor.
- If one volt is present, disconnect ECU connector "A". Measure voltage between terminals A10 and A18. If battery voltage is not present, repair open in White wire between terminal A10 and EGR lift sensor. If battery voltage is present, substitute a good known ECU. If condition goes away, replace original ECU.