Non-Monitored Circuits

Non-Monitored Circuits
The PCM does not monitor the following circuits, systems, and conditions even though they could have malfunctions that result in driveability problems. A diagnostic code may not be displayed for the following conditions. However, problems with these systems may cause a diagnostic code to be displayed for other systems. For example, a leaking fuel injector will not register a diagnostic code directly, but could cause a rich or lean condition. This could cause an oxygen sensor trouble code to be stored in the PCM.

Secondary Ignition*
The PCM cannot detect an inoperative ignition coil, fouled or worn spark plug, ignition cross fire, or open spark plug cable.

Engine Timing*
The PCM cannot detect an incorrectly indexed timing chain, camshaft sprocket, or crankshaft sprocket. The PCM also cannot detect an incorrectly indexed distributor.

Fuel Injectors*
The PCM cannot detect if the fuel injector is clogged, the pintle is sticking, or the wrong injectors are installed.

Fuel Requirements
Poor quality natural gas can cause problems such as hard starting, stalling, and stumble.

PCM Grounds
The PCM cannot detect a poor system ground. However, a diagnostic trouble code may be stored in the PCM as a result of this condition.


Throttle Body Air Flow*
The PCM cannot detect a clogged or restricted air cleaner inlet or filter element.


Exhaust System*
The PCM cannot detect a plugged, restricted, or leaking exhaust system.

Cylinder Compression*
The PCM cannot detect uneven, low, or high engine cylinder compression.

Excessive Oil Consumption
Although the PCM monitors the exhaust stream oxygen content through the oxygen sensor when the system is in a closed loop, it cannot determine excessive oil consumption.

Vacuum Assist*
Leaks or restrictions in the vacuum circuits of vacuum-assisted engine control system devices are not monitored by the PCM. These could result in a MAP sensor message being stored in the PCM.


* NOTE: Any of these conditions could result in a rich or lean condition causing an oxygen sensor trouble code to be stored in the PCM, or the vehicle may exhibit one or more of the driveability symptoms listed in TEST NTC-1A - No Trouble Code Test Menu.