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 over-boost or turbo charger 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).