If your "Service Engine Soon" light has come on in your Pontiac Montana, it means that one of the sensors that monitors myriad functions of your engine, transmission, or exhaust system has recorded a parameter outside of the values that GM considers normal operation. When this occurs, your Powertrain Control Module (PCM) will throw a code-- technically a diagnostic trouble code (DTC)--and activate your Service Engine Soon light to notify you to have your vehicle diagnosed.
Step 1 The Pontiac Montana is equipped with an OBD-II bus which is read by plugging in an OBD-II scanner. The tool is available at auto parts stores or from auto parts departments. Inexpensive units cost less than $50 and can display the code or codes that are causing your Service Engine Soon light to come on. More expensive units are programmed with explanations of the codes, but if the unit you use doesn't have this feature, you can look up the codes online.
Step 2 The OBD-II port is located directly underneath the dash of your Montana on the driver's side. It is a female connection, consisting of 16 pin holes enclosed in hard plastic. Plug the OBD-II scanner cable with the 16-pin male attachment into the OBD-II port. (Some OBD-II scanners are not GM-specific and will require the use of an adapter, usually included with your scanner.) The scanner's connector and the port are both "keyed" so that you cannot connect them backwards.
Step 3 Turn on your OBD-II scanner, then turn your Montana's ignition to "on," but do not start the car.
Step 4 The OBD-II scanner will have a button or a display prompt that asks you if you want to read diagnostic trouble codes. This exact procedure varies from OBD-II scanner to OBD-II scanner.
Step 5 After a brief period of time (usually no more than 10 seconds), the OBD-II scanner will display the result or results. It will include numbers or a combination of letters and numbers, for example, "P0440." If there is more than one DTC, your scanner will prompt you with "See next code?" or a similar message. Write down the DTC or DTCs that the scanner displays.
Look up the DTC explanation using an online list of all GM diagnostic codes. (See resources.) Then, call your mechanic and tell them the DTC explanation. They should be able to tell you if the DTC is major (you should immediately bring your vehicle in for service) or if it is minor (you can wait until a more convenient time to bring your vehicle in for service).
Tips: Some auto parts stores will loan you an OBD-II scanner to check your Service Engine Soon DTCs at no cost.
Warnings: Many OBD-II scanners have the ability to clear DTCs, which will turn off your Service Engine Soon light. This will not make the underlying cause of the DTC go away. It's best to leave the DTCs in the Montana's PCM until you have had your vehicle further diagnosed by a mechanic.
Things You'll Need: OBD-II scanner, Diagnostic Trouble Code (DTC) online resource
