Part 4
ENGINE OBD II MONITORSPositive Crankcase Ventilation (PCV) System Monitor
The PCV monitor consists of a modified PCV system design. The PCV valve is installed into the rocker cover using a quarter-turn cam-lock design to prevent accidental disconnection. High retention force molded plastic lines are used from the PCV valve to the intake manifold. The diameter of the lines and the intake manifold entry fitting are increased so that inadvertent disconnection of the lines after a vehicle is repaired causes either an immediate engine stall or does not allow the engine to be restarted. In the event that the vehicle does not stall if the line between the intake manifold and PCV valve is inadvertently disconnected, the vehicle has a large vacuum leak that causes the vehicle to run lean at idle. This illuminates the MIL after 2 consecutive driving cycles and stores one or more of the following DTCs: Lack of HO2S sensor switches, bank 1 (P2195), Lack of HO2S sensor switches bank 2 (P2197), fuel system lean, bank 1 (P0171) or fuel system lean, bank 2 (P0174).
For additional PCV information, see ELECTRONIC ENGINE CONTROL (EEC) SYSTEM.
Thermostat Monitor
The thermostat monitor is designed to verify correct thermostat operation. This monitor is executed once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction is present, DTC P0125 or P0128 is set and the malfunction indicator lamp (MIL) is illuminated.
The monitor checks the engine coolant temperature (ECT) or cylinder head temperature (CHT) sensor to warm up in a predictable manner when the engine is generating sufficient heat. A timer is initialized while the engine is at moderate load and the vehicle speed is above a calibrated limit. The target timer value is based on ambient air temperature at start-up. If the timer exceeds the target time and ECT or CHT has not warmed up to the target temperature, a malfunction is indicated. The test runs if the start-up intake air temperature from the intake air temperature (IAT) sensor is at, or below the target temperature. A 2-hour engine off soak time is also required to enable the monitor and to prevent erasing of any pending DTCs during a hot soak. This soak time feature also prevents false-passes of the monitor when the engine coolant temperature rises after the engine is turned off during a short engine off soak period.
The target temperature is calibrated to -11°C (20°F) the thermostat regulating temperature. For a typical 90°C (195°F) thermostat, the target temperature would be calibrated to 79°C (175°F). Some vehicle calibrations may lower the target temperature to less than 27°C (50°F) for vehicles that do not warm-up to thermostat regulating temperatures in the 11 °C (20°F) to 27°C (50°F) ambient temperature range.
1. Inputs: ECT or CHT, IAT, engine LOAD (from MAF sensor) and vehicle speed input.
1. Typical monitor entry conditions:
1. vehicle speed greater than 24 km/h (15 mph)
2. intake air temperature at start-up is between -7°C (20°F) and target thermostat temperature
3. engine load greater than 30%
4. engine off (soak) time greater than 2 hours
2. Output: MIL.
Malfunction Indicator Lamp (MIL)
Check Engine, Service Engine Soon, or ISO Standard Engine Symbol
The MIL notifies the driver that the PCM has detected an on board diagnostic (OBD) emission-related component or system malfunction. When this occurs, an OBD DTC sets.
- The MIL is located in the instrument cluster and is labeled CHECK ENGINE, SERVICE ENGINE SOON or the international standards organization (ISO) standard engine symbol.
- The MIL is illuminated during the instrument cluster prove out for approximately 4 seconds.
- The MIL remains illuminated after instrument cluster prove out if:
- If the MIL remains no after the bulb check:
- an emission-related malfunction and DTC exists.
- the PCM does not send a control message to the instrument cluster (applications with the MIL controlled through the communication link).
- the PCM is operating in the hardware limited operation strategy (HLOS).
- The MIL remains off during the instrument cluster prove out if an indicator or instrument cluster malfunction is present.
- To turn off the MIL after a repair, a reset command from the scan tool must be sent, or 3 consecutive drive cycles must be completed without a malfunction.
- For all MIL malfunctions, GO to Symptom Charts.
- If the MIL flashes at a steady rate, a severe misfire condition may exist.
- If the MIL flashes erratically, the PCM can reset while cranking if the battery voltage is low.
- If the MIL flashes erratically, the PCM can reset while cranking if the battery voltage is low.
- The MIL flashes after a period of time with the key in the RUN position (engine not running) if DTC P1000 is set.