The PCM and CCM cannot monitor all of the Base Engine systems and components for faults or conditions that might cause a driveability problem. This handicap can cause confusing diagnostic situations when a Base Engine problem occurs. If the fuel pressure is too low or high, a fuel pressure code will not be set, but a misfire or oxygen Sensor code might be set due to a lean or rich A/F condition.
The PCM cannot detect uneven, low, or high engine cylinder compression. However, a fault in one of these areas could cause the Oxygen Sensor or Misfire Monitor to fail during testing.
The PCM cannot detect a restriction or leak in the Exhaust system. However, a fault in one of these areas could cause the EGR System, Fuel System, O2 or Misfire Monitor to fail during testing.
Fuel Injector Mechanical Fault
The PCM cannot detect if a fuel injector is restricted, stuck open or closed. However, a fault in one of these areas could result in a rich or lean condition and cause the Fuel System or O2 Monitor to fail.
On engines with fuel injection, the fuel pressure regulator controls fuel system pressure. The PCM cannot detect a restricted fuel pump inlet filter, a dirty in-line fuel filter, or a pinched fuel supply or return line. An O2 Sensor or Fuel system code might set due to a lean A/F condition.
Ignition System Secondary
The PCM cannot detect a faulty ignition coil, fouled or worn out spark plugs, ignition wires that are cross firing, or an open spark plug wire. However, the Misfire Monitor would detect these faults during testing.