EGR - CEL P1491 - '97 Accord

BAROB1N

MEMBER
1997 HONDA ACCORD
4 CYL
2WD
AUTOMATIC
188 MILES

My CEL keeps coming on in my '97 Accord. The code is p1491, which is for "Insufficient Lift" in the EGR valve. What I've done so far: I have, using a vacuum gauge, given the EGR @ 6-7 in. HG at idle causing the car to stall. Checked the electrical connections at the EGR solenoid (not valve) and have not seen voltage. I have also connected the EGR solenoid to the batt. And observed vacuum at the EGR valve.

My question is: When does the EGR solenoid get voltage (Under what conditions and how much)? Or, how do can I know for certain it is either the wiring or PCM?

1 Reply

KHLOW2008

MECHANIC
41,814 POSTS

Here are the diagnostic procedures.

DTC P1491: EGR SYSTEM MALFUNCTION

1. Perform PCM reset procedure. Connect SCS service connector. Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral, until radiator fan comes on. Drive vehicle for approximately 10 minutes. Maintain engine speed at 1700-2500 RPM. If DTC P1491 is indicated, go to next step. If DTC P1491 is not indicated, problem is intermittent, system is okay at this time. Check for poor connections or loose wires between EGR valve connector, EGR control solenoid valve connector and PCM.

2. Disconnect No. 16 vacuum hose from top of EGR valve. Connect vacuum pump/gauge to vacuum hose. Start engine and allow to idle. If vacuum does not exist, go to step 4). If vacuum exists, disconnect EGR solenoid valve 2-pin connector. Recheck for vacuum at No. 16 vacuum hose. If vacuum does not exist, go to next step. If vacuum exists, check EGR system hose routing. If hose routing is okay, replace EGR control solenoid valve.

3. Turn ignition off. Disconnect PCM connector "A" (32-pin). Check for continuity between ground and EGR control solenoid valve 2-pin connector terminal No. 2 (Red wire). If there is continuity, repair short in Red wire between EGR control solenoid valve and PCM connector terminal A7. If continuity does not exist, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.

4. Connect vacuum pump/gauge to EGR valve. Start engine, allow engine to idle and apply 8.0 in. Hg vacuum to EGR valve. If engine stalls or runs rough, and EGR valve holds vacuum, go to next step. If engine does not stall or run rough, or EGR valve does not hold vacuum,
replace EGR valve.

5. Turn ignition off. Disconnect EGR control solenoid valve 2-pin connector. Turn ignition on. Measure voltage between ground and control box connector or EGR control solenoid valve connector Black/Yellow wire. If battery voltage exists, go to next step. If battery voltage does not exist, repair open in Black/Yellow wire between EGR control solenoid and appropriate fuse located in underdash fuse/relay box.

6. Reconnect vacuum pump/gauge to No. 16 vacuum hose. Start engine and allow it to idle. Using a fused jumper wire, connect battery voltage to EGR control solenoid valve 2-pin connector Black/Yellow wire terminal. Observe vacuum gauge and connect battery ground to connect EGR control solenoid valve 2-pin connector Red wire terminal. If there is not approximately 8 in. Hg vacuum within one second, go to next step. If there is approximately 8 in. Hg vacuum within one second, go to step 9).

7. Turn ignition off. Inspect No. 16 and No. 24 vacuum hoses for proper routing, leaks or restrictions. Repair hoses as necessary. If hoses are okay, go to next step.

8. Disconnect lower hose on EGR control solenoid valve and connect a vacuum gauge to hose. Start engine and allow it to idle. If there is approximately 8.0 in. Hg vacuum, replace EGR control solenoid valve. If there is not approximately 8.0 in. Hg vacuum, repair No. 24 vacuum hose between intake manifold and EGR vacuum control valve, or replace EGR vacuum control valve.

9. Reconnect EGR control solenoid valve 2-pin connector. Reconnect No. 16 vacuum hose to EGR valve. Start engine and allow it to idle. Using a jumper wire, connect PCM connector "A" terminal A7 and terminal A10. If engine does not run rough or stall, repair open in Red wire between PCM connector terminal A7 or terminal EGR control solenoid valve. If engine runs rough or stalls, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.

You can try cleaning the EGR valve and the ports under it to the exhaust manifold for a start. Any clogging of the ports can cause the trouble codes concerned.