: 2006 STS 3.6 V6 Engine Runs Rough

01-01-13, 05:33 PM
Happy New Year All!

I have a problem with my 06 3.6L V6 running rough. The car had been running great without any issues. I had to change the headlight low beam on the passengers side. I disconnected the negative batter cable. I loosened up the fuse box and moved it a side so I could to get to the headlight assembly to change the burned out bulb. I replace the bulb and re-assembled the car it worked great. The next day drove the car without any incident. I filled it with gas on my way home. Everything was working normally. I got up the next morning to go to work. When I started the car the engine was shacking badly. I backed it out of the garage and it smoothed out and ran normally so I did not think much of it. I drove to work and out to lunch that day. Everything was working great. I drove home without any problems and parked the car in the garage as I always do. Last night my son took my car to pick up his girlfriend from work and called about a minute or two after he left and told me the orange engine light came on and would flash when he accelerated and also ran rough when at idle. I thought maybe I had water in my fuel since I had recently filled the tank. I stopped at Walmart and picked up some heat injector cleaner and fuel deicer to remove the water. I let the car sit about 3 hours and drove it around the neighborhood. Same problem. Someone suggested I change the plugs since I have about 70,000 miles on the car. Same problem as before. I went to the back of the car at idle and it appears to be making noise out of both tail pipes which would lead me to believe I have a sensor or something rather than a single injector problem. The plugs I removed were all dry and brown color as I would expect.

Anyone have a suggestion of anything I am missing? My next step is to take it to a shop. One other odd thing that happened. I took off the negative cable the other day as well as today when I was working on the car. When I reconnect the negative cable the horn begins to honk. It stops when I press the lock button on my key fob. I also had a message on the DIC telling me I had a possible theft attempt. Could the computer be in a less than 100 percent mode due the computer thinking I tried to boost the car?

I am at a loss on this car. Any help would be appreciated.



I did check the engine oil before I changed the headlight and again this morning. I am about 1/2 way between full and add. The car uses a quart every 2000-3000 miles. Nothing I have ever worried about. I just check it on a regular basis. The engine has not been making any odd noises.


01-01-13, 06:07 PM
I doubt it's related to having the battery disconnected. You might have dislodged a vacuum line, probably that was all just a coincidence. The theft warning is common when disconnecting the battery. You must have had a door ajar the first time or security disarmed the first time.

Bad gas is more likely. Now-a-days, Heat or other additives are a waste because it's just adding more alcohol to E10 or worse. Pure gas is getting hard to find. Techron is one of the few useful fuel additives. Use only Top Tier fuel vendors.

If you've had a light, your best step is to read the codes or have it done. It could be lot's of stuff: a flakey coil, worn timing chain, cats, etc.

If you didn't use OEM plugs, you might consider swapping back to the old ones. I know the V8 usually prefers OEM plugs. Is the intake all stock? When was the air filter last changed?

01-01-13, 06:28 PM

Thanks for the reply! The intake is stock and I just replaced the air filter when I did the headlight. I put in Autolite platinum plugs which are the ones called for in the 06 STS. Not sure if they are as good as the OEM's. I will talk with my local repair shop and see when they can get me in to scan for the code is the Techron does not cure the problem.


01-01-13, 08:18 PM
A flashing SES light indicates a misfire was detected, an OBDII scanner will be able to narrow it down to which cylinder(s) misfired.

At that point you'll be able to better troubleshoot the issue.

01-01-13, 09:21 PM
The air filter replacement is a likely source of your issue. The interlocking tabs on the bottom of the airbox are a bit tricky and the intake 'plumbing' can easily pull loose.

I have no use for Autolite parts. I stick with AC/Delco parts but opinions vary.

If you see a flashing light, seek service ASAP.

01-02-13, 06:54 AM
Though it could be a lot of things (some already mentioned), your symptoms may be reflecting a bad crank position sensor or cam position sensor. If not the sensor itself, maybe the wiring to the sensor(s) when you were changing out your light. Since you have an SES light, your first step is to check for any codes.

01-10-13, 07:39 PM
I took it to a local shop and they diagnosed it to a coil pack for number 6 cylinder. They replaced the coil pack and it runs like a new car.

Thanks All for the advice.