1988 Other Toyota Models Check engine light on

Engine Mechanical problem
1988 Other Toyota Models 4 cyl Two Wheel Drive Automatic 133,000km miles

Hi everyone? Hope all are fine wel I have a Toyota Raffine Chaser model 1988 bought recently and serviced now the problem is when I start the car the check engine light does not show up but like driving for 10sec the light turns on and continues to stay on I checked wit a guy who repairs cars he checked the engine but its perfect. But one of my friend told me that the problem might be the timing belt of the engine as he said after 100000km it should be changed so can you guys plz help me out that what exactly is wrong and how to repair it. Thank you