Maint required light is on On a 1988 dodge 318 other then the O2 sensor what else could be the problem?

There are two lights that come on to indicate problems. One says "Maint Required" and the other says "Check Engine." To my knowledge there is no code reader nor is there one required for the 88 (I have never used one on my own 88 318). There are no mechanical/electrical failures that cause the "Maint Required" light to illuminate. It is activated by a timer/mileage box behind the glove box. If you remove the glove box (it will just pull downward out of the way if you push downward on the rear edge before it contacts the stop) the timer box is on the right hand side (I think it's blue). There is a small push button recessed into the box that you need to push with a small pen/screwdriver while the key is in the ON position but the engine is not running. Next time you start the enegine the Maint Reqd light will go out.

Mechanical/electrical problems that throw a code in the computer cause the "Check Engine" light to illuminate. Inserting the key and turning it in the following sequence ON-OFF(but not lock, just back one click)-ON-OFF-ON will cause the Check Engine light to flash in a series of 2-digit codes. Count the flashes and they will give out codes like 12, 37, 55. The Haynes manual has a list of what the codes mean. The codes I listed are the ones my truck always spit out. IIRC 12 is battery recently disconnected, 37 is torque converter lockup circuit (if you have the A727 this is always on because it doesn't have a lockup circuit) and 55 is the End of Codes sequence. The 55 for example is indicated by five flashes of the light, a pause, and another five flashes of the light. This is an OBD1 system so no scanner that I know of will work, and you won't get transmission shifting or fuel cap errors because the trans is not computer controlled and evaporative emissions monitoring is OBDII only.

Answer

There are quite a few components that could cause the light to come on. The best way to deal with it is to plug in a code reader and see what the computer has to say. Code readers are relatively inexpensive and you can even borrow them from some of the DIY auto parts stores.

Answer

Included but not limited to, MAP sensor, throttle position sensor, intermittent ignition control module, transmission shifting problem, fuel cap failure... and the list goes on.