Chrysler PT Cruiser 2001 Service Manual Supplement page 2462

GENERAL INFORMATION
3.2.2 ON-BOARD DIAGNOSTICS
The PCM has been programmed to monitor many
different circuits of the fuel injection system. This
monitoring is called on-board diagnosis.
Certain criteria, or arming conditions, must be
met for a trouble code to be entered into the PCM
memory. The criteria may be a range of: engine rpm,
engine temperature, and/or input voltage to the
PCM. If a problem is sensed with a monitored
circuit, and all of the criteria or arming conditions
are met, then a trouble code will be stored in the
PCM.
It is possible that a trouble code for a monitored
circuit may not be entered into the PCM memory
even though a malfunction has occurred. This may
happen because one of the trouble code criteria
(arming conditions) have not been met.
The PCM compares input signal voltages from
each input device with specifications (the estab-
lished high and low limits of the range) that are
programmed into it for that device. If the input
voltage is not within specifications and other trou-
ble code criteria (arming conditions) are met, a
trouble code will be stored in the PCM memory.
The On Board Diagnostics have evolved to the
second Generation of Diagnostics referred to as
Euro Stage III On-Board Diagnostics.
The following table summarizes the various
Euro Stage III OBD monitors operation.
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