We have a 2006 Toyota Corolla . When we shift into reverse there's quite a clunk; It's not as smooth as it should be. Check engine and Maint Req. lights are on too.

Could be as easy as your car is due for an oil change (if that hasn't been done within the required interval (check your owners manual). If that is not the problem, I suggest taking it to a mechanic that you trust, that has a computer that he can hook to your car to find out exactly what the problem is........ As it could be quite a few different things

A delay of more than a second in shifting from the neutral to drive or reverse gear, could mean that there is a problem with the transmission. If on changing from a neutral or park position to the drive or reverse gear, the car does not immediately catch the gear and move forward or backward, then it could mean a problem in the transmission. If you change gears, and you hear a sudden clunk or sudden jolt or shudder, then the shifting is not smooth and there could be a problem with the gearbox. If the engine rpm keeps increasing but there is no increase in the speed, then it could be a sign of the transmission slipping.Most automatic transmission systems, nowadays, have a check engine light or an OD light, which flashes if there is a problem with the engine.

That warning light usually only service (oil change) reminder.

hi mate , sounds like the SPIGOT bearing its a little bearing that allows the gearbox to be at a different seed than the engine flywheel and if this is in bad condition it will take the gearbox front shaft to a higher speed than comfortable for gearshift , in the meantime when you go for 1st or reverse gear just engage a gear like 4th without taking your foot off the clutch and then go for 1st or reverse, this will stop the gearbox spining long enough for a smooth shif, oNLY USE THIS METHOD WHILE STaTIONARY and see a professional when you get time.

He can't hit a switch and turn on the Check Engine Light, however there are several dozen ways a shoddy mechanic can cause that Light to come on.
Two things you can do is:
1. Disconnect the negative side of the battery and wait about 30-minutes before reconnecting. Check to see if that Light comes back. If not great! If it does:
2. Find out why the Check Engine Light is on. There should be a code that the computer has set. Take it to Autozone or other auto parts stores, where they can hook your vehicle up (for free) to a DRB Scan Tool to eloborate or extrapolate what the Code(s) are.
The real question is if the work the mechanic did caused this. Have their work checked.

it req a new engine ecu.

It should still be under warrenty Take it to the shop for repairs It is a transmisson problem but many things can cause the transmisson not to shift correctly. Call your service department and ask if you should drive it in or have it towed and do not drive till you have it figured out. If you have a warrenty and continue to drive it will void your warrenty.

I am trying to understand your problem. Check engine mounts. Have a driver in the car, hood open. Start car, foot on brakes, shift from park to reverse and back again. Shift through all gears, look for unusual engine movements around engine mounts area. Left foot on brakes, press gas in drive and reverse;watch for excessive engine movements. Be careful as you perform these steps. You may also want to check drive axles. Keep me updated.

To reset the system. Turn the ignition key to the "OFF" position with the odometer reading shown. Turn the ignition key to the "ON" position while holding down the trip meter reset knob. Hold down the knob for at least 5 seconds. The odometer indicates "000000" and the light goes off. If the system fails to reset, the light will continue flashing.

That is for oil changes. It come on when the oil change is due.
When you have your oil change done, the lube tech should reset the this light every time.
If you need help resetting the light, let me know.