On-Board Diagnostics
The PCM monitors several different engine control system circuits. If malfunction occurs, PCM will store a DTC when malfunction is detected, and PCM will enter limp-in mode. In limp-in mode, PCM substitutes values for failed component to continue engine operation, but loss of good driveability may result.
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 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 DTC will be stored in PCM. The following monitors are used:
- EGR Monitor (Diesel)
- 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 run/stop engine cycles with engine coolant temperature at least 160°F (71°C) on normal operation, or 80 run/stop engine cycles with engine coolant temperature at least 160°F (71°C) on engine misfire or fuel system monitor.
PCM also records and stores engine operating conditions when malfunction occurred. This information is referred to as freeze frame data. If malfunction is an engine misfire or fuel system rich or fuel system lean, freeze frame data will be updated with the most current information regarding these failures. Freeze frame data recorded is:
- Fuel System Status
- Load Value (Displayed As Percent)
- Long Term Adaptive (Displayed As Percent)
- Short Term Adaptive (Displayed As Percent)
- Absolute MAP (Displayed As Percent)
- Engine RPM
- Vehicle Speed Sensor
- DTC During Data Recording
DTCs may be retrieved for system diagnosis by using scan tool only. See RETRIEVING DTCS under SELF-DIAGNOSTIC SYSTEM. By using scan tool, self-diagnostic capabilities of this system can simplify testing and reduce diagnostic time. System malfunctions are identified as either hard failures or intermittent failures.