Code 12: EGR System
- Turn ignition off. Remove fuse No. 15 (ACG) from fuse in underdash fuse box for 10 seconds to reset ECU. Warm engine until cooling fan comes on. Road test vehicle for about 10 minutes, keeping engine speed approximately 1700-2500 RPM. Check ECU for fault codes. See RETRIEVING CODES
. If Code 12 is not present, problem is intermittent. Check for poor connections at ECU connector, EGR valve connector or control box connector.
- Test drive vehicle and retest. If Code 12 is present, start engine. Disconnect vacuum No. 11 hose from EGR valve. Refer to Fig 1
. Start engine. Disconnect vacuum No. 11 hose from EGR valve. Connect vacuum gauge to hose. If no vacuum is present, go to step 4). If vacuum is present, disconnect 4-wire connector from control box. Check vacuum again on No. 11 hose. If vacuum is present, check vacuum hose routing.
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- If routing is okay, replace EGR control solenoid valve. If vacuum is not present, turn ignition off. Remove connector "A" from ECU. Using an ohmmeter, check for continuity between White wire terminal of 4-wire connector and ground. If continuity is present, repair short in White wire between EGR control solenoid valve and ECU connector terminal No. A11. If continuity is not present, substitute a known good ECU. If system operates properly, replace original ECU.
- If vacuum is not present during first vacuum test in step 2), install vacuum pump on EGR valve. With engine idling, apply 8 in. Hg to EGR valve. If engine does not stall/run rough and EGR valve does not hold vacuum, replace EGR valve.
- If engine stalls/runs rough and EGR valve holds vacuum, disconnect 4-wire connector from control box. Measure voltage between Black/Yellow wire terminal and body ground. If battery voltage is not present, repair open in Black/Yellow wire between solenoid valve and fuse No. 22.
- If battery voltage is present, install "T" fitting into No. 11 vacuum hose. Attach vacuum gauge to "T" fitting. Start engine and allow to idle. Connect battery voltage to terminal "A" of control box connector. See Fig 2
. While observing vacuum gauge, connect terminal "B" to negative battery terminal.
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- If gauge reads 8 in. Hg within one minute, go to step 9). If gauge does not read 8 in. Hg within one minute, turn ignition off. Inspect hoses for leaks, restrictions and misrouting. Repair as necessary. If hoses are okay, disconnect lower hose on EGR control solenoid valve.
- Connect vacuum gauge to hose. See Fig 3
. Start engine, and allow to idle. If 6-10 in. Hg is not present, replace Constant Vacuum Control (CVC) valve. See Fig 3
. If 6-10 in. Hg is present, replace EGR control solenoid valve. See Fig 3
.
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- If gauge reads 8 in. Hg in step 7), turn ignition off. Reconnect 4-wire connector. Connect EGR Test Harness (07LAJ-PT3020A) between EGR valve lift sensor and vehicle wiring harness connector. See Fig 4
. Turn ignition on. Measure voltage between Red (+) wire and Green (-) wire. If about 5 volts are not present, repair open in Yellow/White or Green/White wire between EGR valve and ECU connector. If about 5 volts are present, go to step 10).
- Turn ignition on. Measure voltage between White (+) and Green (-) test terminal. If 1.2 volts are not present, check for defective EGR valve, ECU or short in Black/White wire between ECU connector terminals D12 and EGR lift sensor. If 1.2 volts are present, observe voltmeter, and apply 8 in. Hg to EGR valve. Voltage should increase to about 4.0 volts. If voltage is not correct, replace EGR valve. If voltage is correct, go to step 11).
- While observing voltmeter, apply 8 in. Hg to EGR valve and release. Repeat procedure several times. If voltage does not consistently increase and decrease as vacuum increases and decreases, replace EGR valve. If voltage does increase and decrease with vacuum, reconnect No. 11 hose to EGR valve.
- Turn ignition off. Connect ECU Test Harness (07LAJ-PT3010A
) between ECU and ECU connector. See Figure
. Start engine and allow to idle. Measure voltage between test terminals A12 (+) and A22 (-). If about 1.2 volts are not present, repair open in Black/White wire between ECU connector terminal D12 and EGR valve lift sensor.
- If about 1.2 volts are present, connect jumper wire between test terminals A11 and A26. If engine does not stall, repair open in White wire between ECU connector A11 and EGR control solenoid valve. If engine stalls, substitute a known good ECU. If symptom/condition goes away, replace original ECU.
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