Problem started when I was driving and my oil light came on car started barely driving then I hard to pull off the road. Car leaks \burns oil so I thought I was low. Poured a qrt, didn't work. Put a little bit of gas in and it started. I kept driving and the steering wheel was extremely hard to turn. Well I parked it for a day and went to drive, a mile later the traction lights came on all of them. Went to accelerate and had very little power . then all lights in the dash came on and stayed on I hit a stoplight and went to accelerate but almost no power. Had to pull over turn the car off. Car wouldn't start for a good hour. Went to start and it started I turned it off. Tried again and wouldn't start. Got it towed. I cleaned off my terminals they were corroded but didn't help. It got jumped fine and backed it into parking spot just fine. Now won't start again . I'm gonna jump here soon but its a BRAND NEW BATTERY. Also every once in a while I start the car in the AM the first try it does crank.works on second try. 166,000 miles no extra elect. Add ons. All stock. Its deff due for a oil change tho.
When car would start as I try to crank the headlights flicker.

 

get your battery terminals cleaned and re tightened. Check the signal wire on starter, it is the one that comes back up with the positive side to battery from starter.
It goes to starter and is connected by a small connector, this cruds up and then no signal is given.
I have just parked my cx7 up in a neighbors yard till I pay the last 2 months off. It failed MOT due to silly high emissions. I had replaced pcv valve, turbo, inlet manifold. car was running sweet and had lower fuel usage, but it failed the emissions on MOT. so when 2 months are up I am going to scrap the car....... I spent £1500 on it but to no avail. I lost all faith in it.
Have to say I had asked questions on here, but rarely got a reply.....anyway, good luck mate.