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Code 12 - EGR System

  1. Check harness and connections between EGR valve and ECU. Warm engine to normal operating temperature (cooling fan on). Disconnect vacuum hose from EGR valve. Using a hand-held vacuum pump, apply vacuum to EGR valve. If vacuum does not hold, and engine does not stall, replace faulty EGR valve or clean blocked EGR passages.
  2. If vacuum held and engine stalled in step 1), connect vacuum gauge to EGR supply hose. Start engine. If vacuum is present, inspect EGR vacuum hose routing. If okay, test EGR control solenoid valve. If vacuum is not present, go to next step.
  3. Disconnect 2-wire connector from control box. Supply battery voltage to Black/Yellow wire terminal of box and ground to Red wire terminal of box. Reading at EGR valve hose should now be about 8 in. Hg. If okay, go to step 5). If not, go to step 4).
  4. If vacuum reading is not correct, remove control box cover and disconnect hose between CVC valve and air chamber and connect vacuum gauge to air chamber. If 8 in. Hg is present, replace EGR solenoid. If not, inspect vacuum hoses for kinks and proper connection. If okay, replace CVC valve.
  5. Measure voltage between Black/Yellow terminal on main wire harness and ground. If battery voltage is present, go to step 6). If battery voltage is not present, repair open in Black/Yellow wire between solenoid valve and No. 1 fuse.
  6. If battery voltage is present, turn ignition off. Connect test harness between EGR lift sensor and sensor harness connector. Turn ignition on. Measure voltage between Red (pos.) and Green (neg.) terminals. If voltage is about 5 volts, go to step 8). If voltage is not about 5 volts, measure voltage between ground and Red terminal. If voltage is now about 5 volts, repair open in Green/White wire between ECU terminal C12 and sensor.
  7. If voltage is not about 5 volts, turn ignition off. Connect ECU test harness between ECU and ECU connector. See Figure . Measure voltage between terminals C13 (pos.) and C12 (neg.). If voltage is now about 5 volts, repair open in Yellow/White wire between ECU terminal C13 and sensor. If voltage is not about 5 volts, substitute a known good ECU. If condition is rectified, replace original ECU.
  8. Measure voltage between White (pos.) and Green (neg.) terminals. If voltage reading is not about one volt, replace EGR valve or repair short in Yellow wire between ECU terminal C8 and EGR control lift sensor. If about one volt is measured, turn ignition off. Connect ECU test harness between ECU and ECU connector.
  9. Turn ignition on. Measure voltage between ECU terminals C8 (pos.) and C12 (neg.). See Figure . If voltage is not about one volt, repair open in Yellow wire between ECU terminal C8 and sensor. If voltage is about one volt, disconnect connector "A" from ECU side only.
  10. Measure voltage between terminals A10 (pos.) and A18 (neg.). If battery voltage is not present, repair open or short in Red wire between ECU terminal A10 and EGR control solenoid. If battery voltage is present, substitute a known good ECU and recheck. If condition is rectified, replace original ECU.
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