Non-Monitored Circuits

The PCM does not monitor all circuits, systems and conditions that could cause a malfunction or driveability problem. However, problems with these systems may cause the PCM to store diagnostic trouble codes for other systems or components. For example, a fuel pressure problem will not register a fault directly, but could cause a rich/lean condition or misfire. This could cause the PCM to store an oxygen sensor or misfire diagnostic trouble code. The major non-monitored circuits are identified as follows.

1. Cylinder Compression
   
   The PCM cannot detect uneven, low or high cylinder compression. Low compression lowers oxygen content in the exhaust which leads to fuel system, oxygen sensor or misfire detection fault.
2. Excessive Oil Consumption
   
   Although the PCM monitors engine exhaust oxygen content when the system is in closed loop, it cannot determine excessive oil consumption.
3. Exhaust System
   
   The PCM cannot detect a plugged, restricted or leaking exhaust system, although it may set a diagnostic trouble code for EGR, oxygen sensor or fuel system fault.
4. Fuel Injector Mechanical Malfunctions
   
   The PCM cannot determine if a fuel injector is clogged, needle is sticking or if the wrong injector is installed. However, these could result in a rich or lean condition causing the PCM to store a diagnostic trouble code for a misfire, oxygen sensor or fuel system.
5. Fuel Pressure
   
   The fuel pressure regulator controls fuel system pressure. The PCM cannot detect a clogged fuel pump inlet filter, clogged in-line fuel filter, or a pinched fuel supply. However, these could result in a rich or lean condition causing the PCM to store an oxygen sensor, or fuel system diagnostic trouble code.
6. PCM Connector Engagement
   
   The PCM may not be able to determine spread or damaged connector pins. However, it might store diagnostic trouble codes as a result of spread connector pins.
7. PCM System Grounds
   
   The PCM cannot determine a poor system ground. However, one or more diagnostic trouble codes may be generated as a result of this condition. The module should be mounted to the body at all times, also during diagnostics.
8. Secondary Ignition Circuit
   
   The PCM cannot detect an inoperative ignition coil, fouled or worn spark plugs, ignition cross firing or open spark plug cables. The misfire will however, increase the oxygen content in the exhaust, deceiving the PCM into thinking the fuel system is too lean.
9. Throttle Body Airflow
   
   The PCM cannot detect a clogged or restricted air cleaner inlet or filter element.
10. Vacuum Assist
    
    The PCM cannot detect leaks or restrictions in the vacuum circuits of vacuum assisted engine control system devices. However, these could cause the PCM to store a MAP sensor diagnostic trouble code and cause a high idle condition.