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
The Powertrain Control Module (PCM) monitors several different engine control system circuits. If malfunction occurs, PCM may store a Diagnostic Trouble Code (DTC) when malfunction is detected, and PCM will enter limp-in mode. In limp-in mode, PCM substitutes values for failed component and provides continuous engine operation.
The PCM contains electronic circuit monitors that monitor fuel, vehicle emissions, engine and ignition system performance. Monitors use information from various sensor circuits for system monitoring. Monitors do not indicate a specific component failure, but do indicate an implied failure within a specified system, and that the problem must be diagnosed. If any monitor detects a problem affecting vehicle emissions, a Diagnostic Trouble Code (DTC) will be stored in PCM. The following monitors are used.
- EGR Monitor
- Engine Misfire Monitor
- Fuel System Monitor
- Oxygen Sensor Monitor
- Oxygen Sensor Heater Monitor
- Catalyst Monitor
- EVAP System Leak Detection Monitor
The PCM will erase DTC once MIL is turned off. Once MIL is turned off, PCM must not detect the recent malfunction during 40 warm-up cycles on normal operation, or 80 warm-up cycles on engine misfire or fuel system monitor.
DTCs may be retrieved for system diagnosis. SeeRETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. System malfunctions are identified as either hard failures or intermittent failures.
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.