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.
Engine Controls Self-Diagnostics - Introduction: Introduction: OBD-II
PCM detects malfunctions related to engine sensors or actuators. OBD-II continuously monitors emission related components and can set Diagnostic Trouble Codes (DTCs), 1st trip DTCs, Freeze Frame data, 1st trip Freeze Frame data and SRT codes. This data, or DTC information, can be retrieved to assist in diagnosing problems. Using the Malfunction Indicator Light (MIL) to diagnose system faults is limited to code retrieval and fuel monitoring and is not recommended. It is recommended to use a OBD-II Generic Scan Tool (GST), or Nissan's CONSULT scan tool when performing self-diagnostic procedures, clearing PCM or performing a System Readiness Test (SRT).
When a malfunction is detected for the first time, the 1st trip DTC and 1st trip freeze frame data are stored in Powertrain Control Module (PCM) memory. However, in most 1st trip instances MIL will not be illuminated. If the same malfunction is detected, on the next vehicle trip, MIL will be illuminated as soon as the DTC is detected, or 2nd trip detection logic. If a misfire or fuel system malfunction should occur during 1st trip, MIL will be illuminated or flash. DTC and freeze frame information will be stored to aid in diagnostics by specifying operating conditions when DTC was set.
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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.
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