I have a toyota sienna 2001 model,and the engine light comes on every two days after i disconnect the baterry terminals and or after i have driven it for certain miles.what could be the problem and try to fix it myself to avoid high cost of repairs. Thanks and i appreciate any suggestion..

You should have the error code read from the vehicle's computer (a code scanner is needed for this). If you constantly are disconnecting the battery, some manufacturers program an error code in the computer indicating that the battery has been disconnected within the last XX number of starts. If the code is P1600 or P1630, this is probably your problem. If you're disconnecting the battery for security reasons, either install an aftermarket security/anti-theft system or realize that the check engine light will keep coming on.

normally to reset a check engine light all you have to do is unhook the battery for a couple of minutes and then hook it back up. if you are having a sensor problem though this check engine light will come back on after you drive the vehicle for more than 3 minutes.

Mine is a 2001 Sienna LE. I got the P0420 code and the dealer want to replace an engine control computer for $1600. I've found posts that say you can replace your oxygen sensors, which still costs around $100 each. The P0420 seems to be emissions related. When my check engine light comes on, I run the highest grade, no ethanol gas, and usually within a couple of tanks, the light goes off again. The last time it happened about 2 wks ago, I put in the 93 octane no ethanol premium and a can of Seafoam and within a half a tank, the light went out. Your problem might be more serious, and I don't know what the 1150 code is, but so far that's worked for me.

the engine light on means your car has the obd2 code problem you need to check out the code and delete it, i know this tool is helpful for your car, or you can take your car to toyota dealer to read out the code.

Have the same problem on my 2001 Sienna with 184k miles. Knock sensor is the p0330 or p0325 code. Here is a walkthrough of the fix:
http://www.findonefindall.com/toyota-sienna/toyota_knock_sensor.htm

CALL YOUR LOCAL AUTO ZONE-THEY CAN LOOK UP THE CODE FOR YOU

P0420=Catalyst System Efficiency Below Threshold Bank 1,
The air filter is not the cause here,this is just a code saying your converter is not doing its best,

take it to the work shop

Toyota Specific Trouble Codes
P1135 Air/Fuel Sensor Heater Circuit Response. (Bank 1 Sensor 1)
If you have changed the proper sensor then you may need to have the cam shaft looked at.

U can either turn it off with a engine scan tool or disconnect the battery for 5 min's, if u disconnect the battery u may activate your anti-theft systems, so I recommend u have it turned off with a scan tool. A quick note: If the problem in the engine controls that turned the light on is not repaired the light will come back on in 20-30 miles.