My Accord 99 V6 was throwing P1491 "Insufficient EGR lift detected" for quite a while now. It did it once last winter, I reset the code, and it didn't come back until this January, and since January it's very persistent: comes back three trips after each reset, so I decided to do smth about it.

I'm aware of the TSB suggesting that EGR passages should be cleaned in the intake manifold whenever P0401 (Insufficient EGR flow) or P1491 is raised. I'm kind of puzzled why TSB mentions P1491. It seems to be purely EGR valve related. Really, how can the blockage of EGR passages affect the degree to which the valve opens?

Nevertheless, I decided to try approaching the dealer with the TSB and asking them to perhaps do the cleaning for free despite me having 93K on the odometer (and extended warranty ending at 80K). Well, that didn't work out very well. They said that they need to call Honda, and for that they need to read the codes (even though I already gave P1491 to them), and that will be $80, and even after doing it, according to him, chances of getting approval from Honda are slim. Errrr. That's after me doing all service there and paying them to change my timing belt month ago.

After the failure at the dealership I decided to actually take a look at the EGR valve. Unscrewing it didn't reveal any gunk or excess of carbon deposits: everything was pretty clean. Maybe I'll post some pictures later, but it was really clean. I also verified that the valve actually opens when 12V is applied to pins 4 and 6. Then I followed the troubleshooting chart from Alldata, measured resistance between pins 1, 2 and 1, 3 and verified that there are no shorts or infinity between them. Applied voltate to 4 and 6 while the engine was idling, and it almost died, which is a good sign according to the flowchart (it confirms that the valve actually opens and that the EGR flow is there).

So, according to Alldata, my valve works just fine, and the only thing left to blame is the ECU, which I'm just afraid to blame given how much it will cost me to replace it

I could try cleaning the EGR passages in the manifold myself, but given the pristine state of the EGR valve and that the engine actually reacts to me opening the valve at idle, I think it will be a wasted effort.

I think there's got to be more troubleshooting I could do before actually taking the manifold apart. Alldata's flowchart mainly targeted the valve and the state of wires going from the valve to the ECU. It didn't suggest any vacuum tests, for example. Is there anything else I can look at? Haynes avoids this topic, I hear that Helm may have more troubleshooting charts. If anyone has an electronic version of Helm, could you please, please copy/paste the chart?

Thanks!