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Non-Monitored Circuits

The PCM does not monitor following circuits, systems, and conditions even though they could have malfunctions that result in driveability problems. A diagnostic code may not be displayed for following conditions. However, problems with these systems may cause a diagnostic code to be displayed for other systems. For example, a fuel pressure problem 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 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 Pressure (*)  - Fuel pressure is controlled by vacuum-assisted fuel pressure regulator. The PCM cannot detect a clogged fuel pump inlet filter, clogged in-line fuel filter, or a pinched fuel supply or return line.

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

Fuel Requirements  - Poor quality gasoline can cause problems such as hard starting, stalling, and stumble. Use of methanol-gasoline blends may result in starting and driveability problems.

PCM Grounds  - The PCM cannot detect a poor system ground. However, a diagnostic trouble code may be stored in 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 PCM monitors exhaust stream oxygen content through oxygen sensor when system is in a closed loop, it cannot determine excessive oil consumption.

Evaporative System (*)  - The PCM cannot detect a restricted, plugged, or loaded evaporative purge canister.

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

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