If the MIL is on along with DTC P0401 (insufficient EGR flow) or DTC P1491 (EGR system malfunction) on a '94-96 Accord or '95-96 Odyssey, do these checks: 1. From the PGM Tester freeze data display, check the EGR VLS (exhaust gas recirculation valve lift sensor) voltage.
? For DTC P0401, if the EGR VLS reads more than 3.0 V, clean (unclog) the EGR passages. If it reads less, go to step 2.
? For DTC P1491, if the EGR VLS reads more than 2.0 V, replace the EGR valve. If it reads less, go to step 2. 2. Disconnect the vacuum hose from the EGR valve, and attach it to a vacuum gauge.
3. Backprobe the RED wire in the EGR control solenoid valve connector, then start the engine, and let it idle.
4. While watching the vacuum gauge, apply and remove ground to the RED wire 10 times.
? Does the gauge read 6 inches of vacuum within 1 second of grounding the RED wire? YES - Go to step 5. NO - Replace the EGR control solenoid valve, and clear the DTC.
5. Remove the backprobe, and apply 6 inches of vacuum to the EGR valve.
? Does the EGR VLS reading go to 1.2 V and stay there? YES - Replace the EGR valve, and clear the DTC. NO