96 Buick Century with P1406 code (and occasional P0300/P1406 Pendings)

Okay, I thought I’d resolved this recently, but had an old problem crop back up, so I’m hoping someone here might have some ideas… I have a 1996 Buick Century Custom 3.1L V6 with about 93k miles. As background, I’ve done quite a bit of work to the car in the last month and a half - replaced the engine with a rebuilt, replaced the catalytic converter (that was damaged when the old engine misfired badly), replaced my ignition control module and two coils, and replaced my fuel injectors as a couple weren’t firing well. In addition, I replaced my EGR valve to resolve a P1406 (EGR Valve Pintle Position Sensor) code that came up last month (the original EGR valve looked to have quite a bit of carbon buildup, and was likely original to the car from 1996). That replacement was done about 9/25, and my check engine light came on again this week. Now it’s showing a P1406 (EGR Valve Pintle Position Sensor) code, and occasionally (maybe every 2-3 starts) will also have a P0300 random intermittent misfire and P1406 code shown as pending. In terms of running/performance, if I leave the car in park and give it gas once I get the pedal to about 1/2 down, around about 1800RPM, it sounds almost like it’s coughing, and that’s also the case if I leave the car running and go listen/feel at the tailpipe, the exhaust seems to pulse rather than being just a steady stream. Performance wise on the road I haven’t noticed any major problems - the car seems to run alright, I haven’t noticed any serious misfires or performance problems, seems to have good acceleration, etc.

The one thing I will mention is when the catalytic converter was replaced the shop mentioned that my O2 sensors may need to be replaced as well down the road, as it’s possible that they were damaged when the old catalytic converter was. When I checked the live data on my scan tool I do see what seem to be good values from both O2 sensors (

I’d love to hear any ideas on the next steps for troubleshooting or thoughts of what this could be. I’m not an expert DIY’er, but do my own oil changes and brake jobs, and did manage to replace the EGR valve and one of my coils myself, and I also have a fairly good scan tool (that shows live and freeze frame data) so I’ve got some knowledge/experience. I’d greatly appreciate anybody’s thoughts if you have ideas.


I would be chasing an EGR valve issue on the assumption that the new one has a problem - or that the valve itself (the actual part) never was the problem to begin with.

If you managed to replace it you can probably follow these directions.

Hi Cig,
Yup, I looked over the site and it’ll be easy enough for me to follow. Just need to figure out which box my DMM made it into, as I’m getting ready to move. Or just go and pick up a new one. Thanks for the suggestion, I’ll give you an update when I make it through the testing process and figure out if I just bought a bad EGR valve or if there’s some other issue in the loop somewhere.

Okay, I am officially an idiot.

Went to run those tests today, only to realize that when I re-installed the EGR valve after cleaning it and replacing the gasket last week I installed it with the connector pointing towards the rear – exactly backwards. Switched it around so it’s actually installed the correct way and it immediately resolved all the problems – no performance issues at all, no codes either pending or current, even after spending the day running the car through a couple of complete drive cycles, etc.

Looks like I get to chalk this one up to the mechanic (me!) not paying enough attention and doing something colossally stupid. I’m just glad it didn’t damage anything major, and I caught it before I wound up having to spend a ton on diagnostics. I did go ahead and walk through those tests, after I put the EGR valve back on correctly, and everything tested fine, no problems.

Thanks Cig!

Glad you got it worked out. I don’t think you should worry too much about having made a mistake though. I’m everyone has done worse than this. I know I have

Looks like cigroller got you going in the right direction and you’re not an idiot for making a mistake. On the contrary, you were astute enough to go back and find the problem whereas many people might have wrestled it for weeks before throwing in the towel and having the car towed to a shop or worse; maybe even scrapping the car.
(I had a guy bring a small block Chevy in once in which he had pulled the engine and removed the cylinder heads on the assumption that the motor was running poorly because of a compression problem. The cause? Two bad plug wires. Ouch.)

Everyone makes mistakes now and then, even mechanics, and any mechanic who says he hasn’t is lying through his teeth. I’ve made a few but thankfully nothing major in scope other than an embarassing one to this day error I made about 10 years back. Memory just won’t let that one die. :wink: