Non-Monitored Circuits

The PCM and/or the ECM will not monitor certain malfunctioning circuits or components that could cause driveability problems. Also, a Diagnostic Trouble Code (DTC) might not be stored for these malfunctions. However, problems with these circuits or components may cause the PCM/ECM to store DTC's for other circuits or components. EXAMPLES: A cylinder with low compression will not set a DTC directly, but may cause an engine misfire. This in turn may cause the ECM to set a DTC for an engine misfire. Or, a dirty or plugged air filter will not set a DTC directly, but may cause lack of turbocharger boost. This in turn may cause the ECM to set a DTC for a boost pressure malfunction.

Fuel Pressure
Primary fuel pressure from the fuel tank to the fuel injection pump is supplied by the low-pressure fuel transfer pump. High-pressure to the fuel injectors is supplied by the fuel injection pump. The ECM cannot detect actual fuel pressure, a clogged fuel filter, clogged fuel screen, or a pinched fuel supply or return line. However, a DTC may be set due to an engine misfire.

Cylinder Compression
The ECM cannot detect uneven, low, or high engine cylinder compression. However, these could result in a possible misfire which may set a DTC.

Exhaust System
The ECM cannot detect a plugged, restricted or leaking exhaust system. However, DTC's may be set for engine misfire, high intake manifold temperature, high engine coolant temperature, turbocharger overboost or turbocharger underboost.

Fuel Injector Mechanical Malfunctions
The ECM cannot determine if a fuel injector is clogged, the needle is sticking or if the wrong injector is installed. However, these could result in a possible misfire which may set a DTC.

Excessive Oil Consumption
The ECM cannot determine excessive oil consumption. However, if excess oil consumption is high enough, it could result in a possible engine misfire which may set a DTC.

Air Flow
The ECM cannot detect a clogged, restricted or dirty air filter element, or a restriction in the air inlet system. However, these could result in a possible misfire which may set a DTC.

Air Pressure Leaks
The ECM cannot detect leaks or restrictions in the air intake system. However, these could cause the ECM to store a Manifold Air Pressure (MAP) sensor DTC (boost pressure problem detected).

PCM/ECM System Grounds
The PCM/ECM cannot directly determine poor system grounds. However, one or more DTC's may be generated as a result of poor grounds.

PCM/ECM Connector Engagement
The PCM/ECM may not be able to determine spread, damaged or corroded connector pins. However, it might store DTC's as a result of spread connector pins (circuits that are open).