2004 Chrysler Grand Voyager engine light

The Engine Computer detected a problem, set a diagnostic fault code, and turned the Check Engine light on to tell you. There's over a thousand potential fault codes. Some have very minor causes. Some can be serious. The first thing you have to do is find out what that code is. If it set as soon as you had the repair done, the mechanic should have seen the light and investigated. The code is most likely related to something he just had apart and forgot to reconnect.

Even if this fault code has a minor cause, it could turn serious if neglected. Also, if a totally different problem occurs while you're driving that IS serious, how would you know since the light is already on?

The time to stop the engine immediately is when the Check Engine light is flashing. That means too much raw fuel is going into the exhaust system and is going to damage the expensive catalytic converter. When the light is on but not flashing, it's okay to drive it back to the shop, but I'd be nervous driving it for long distances until I knew which code was set.

Codes can also be set if the ignition switch was turned on during the recent service while something was disconnected. Chrysler has always made reading engine codes yourself much easier than any other manufacturer. I never did this though on an '06 model, but it should be the same. On '95 and older models you have to count the flashes of the Check Engine light. For '96 and newer, cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine, leave it in "run", then watch the three-digit codes appear in the odometer display.

You didn't say which engine you have so you'll just have to look on the intake plenum or fresh air tube. That sensor practically never fails unless it's handled very roughly. By far the most common cause of that fault code is the sensor was unplugged. It will have a two-wire plug

Fuel doesn't vaporize easily in colder weather, and the air is more dense. Both of those conditions require more fuel to enter the engine. That's why the Engine Computer needs to know air temperature. When it doesn't know the temperature, it's going to command plenty of fuel to insure the engine runs right, whatever the temperature is. That means you'll be using more fuel than necessary. The computer will get an idea of air temperature from the coolant temperature sensor when the engine is first started, but the fault code will prevent some other self-tests from running because the computer needs the IAT to make comparisons. That is more likely to become a problem when people ignore the Check Engine light for weeks or months. That gives a totally new problem time to occur, but it may not be detected because of those tests that fail to run. Then, when the first problem is finally repaired, the customer picks up the vehicle, then the Check Engine light turns right back on again. Of course they assume the car wasn't repaired properly, but in reality the mechanic had no way of knowing there was another problem.

The Check Engine light should turn off once the sensor is reconnected, and the ignition switch is turned off and back on. Normally the fault codes will erase automatically after a certain number of engine starts, but if it doesn't, you may need a scanner or code reader to erase it.