Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
On-Board Diagnostics: Notes
The Malfunction Indicator Light (MIL) is located on the right side of instrument cluster. The MIL is also referred to as SERVICE ENGINE SOON indicator. The MIL is controlled by the Powertrain Control Module (PCM) and is used to indicate that the PCM has detected a problem that affects vehicle emissions and a Diagnostic Trouble Code (DTC) is present. When ignition is first turned on, MIL should come on and remain on until engine is started to verify bulb and circuit operation. If MIL does not illuminate at all, diagnose MIL circuits. See MALFUNCTION INDICATOR LIGHT INOPERATIVE under SYSTEM TESTS. The PCM is programmed with test routines that check the operation of the various systems that the PCM controls. Some tests check the internal functions of the PCM. Some tests are run continuously while other tests run only under specific conditions (referred to as code enable criteria). When vehicle is operating within conditions for running a particular test, the PCM checks certain parameters and determines whether or not the values are within an expected range. When conditions for setting the DTC are met, the PCM will store a DTC and, if code is emission related, illuminate the MIL. Some DTCs alert the driver via a message. See CODE TYPES . The PCM also saves data and input parameters when most DTCs are set. This data is stored in FREEZE FRAME and/or FAILURE RECORDS. See FREEZE FRAME and FAILURE RECORDS .
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.