Vibe L4-1.8L VIN L (2003)
step in diagnosing any engine control system problem is to remove all aftermarket electrical equipment from the vehicle. Diagnosis may proceed in the
normal manner after eliminating aftermarket equipment as a cause of the engine control system malfunction.
Electrostatic Discharge (ESD) Damage
NOTE: In order to prevent possible Electrostatic Discharge damage to the PCM, Do Not touch the connector pins or the soldered components on the
circuit board.
Electronic components used in the engine control system are often designed to operate at very low voltages. Electronic components are susceptible to
damage caused by electrostatic discharge. Less than 100 volts of static electricity can cause damage to some of the electronic components. There are
several ways for a person to become statically charged. The most common methods of charging are by friction and by induction. An example of
charging by friction is a person sliding across a car seat. Charging by induction occurs when a person with well insulated shoes stands near a highly
charged object and momentarily touches ground. Charges of the same polarity are drained off leaving the person highly charged with the opposite
polarity. Therefore, use care when handling and testing electronic components in order to avoid electrostatic charges that can cause electronic
component damage.
Input Components
The PCM supplies a buffered (reference) voltage to the various information sensors and switches. The PCM monitors the input components for circuit
continuity and out-of-range values. The PCM also provides performance checking. Performance checking refers to the PCM indicating a fault when
the signal from an input does not seem reasonable, i.e., a throttle position (TP) sensor that indicates a high throttle position at low engine loads or low
manifold absolute pressure sensor voltage. The input components may include, but are not limited to the following sensors and switches:
-
The crankshaft position (CKP) sensor
-
The throttle position (TP) sensor
-
The engine coolant temperature (ECT) sensor
-
The camshaft position (CMP) sensor
-
The mass air flow (MAF) sensor
-
The heated oxygen sensor (HO2S)
-
The fuel tank pressure (FTP) sensor
-
The knock sensor (KS)
-
The vehicle speed sensor (VSS)
-
The power steering pressure (PSP) switch, if equipped
-
The transmission range switch (A/T only)
-
The A/C compressor control module (A/C relay)
Output Components
The PCM is responsible for the control and operation of many output components. The PCM controls many components with an electronic switch
called an output driver that completes a ground circuit when turned ON. The PCM monitors the output components for the proper response to the
PCM commands. Components where functional monitoring is not feasible will be monitored for circuit continuity and out-of-range values if
applicable.
Output components to be monitored include, but are not limited to the following circuits:
-
The idle air control (IAC) valve
-
The CMP actuator solenoid valve
-
The circuit opening relay
-
The malfunction indicator lamp (MIL) control
-
The A/C compressor control module (A/C relay)
-
The electronic transaxle controls
Catalyst Monitor Diagnostic Operation
The powertrain control module (PCM) uses certain diagnostic strategies known as primary system based diagnostics that evaluate the various primary
system operations. The primary system based diagnostics also evaluate the various primary system operations affect on vehicle emissions. Some of the
primary system based diagnostics are listed here with a brief functional description of the diagnostics involved.
The OBD 2 catalyst monitor diagnostic measures the oxygen storage capacity of the 3-way catalytic converter (TWC). Heated oxygen sensors (HO2S)
are installed before (pre-catalyst) and after (post-catalyst) the TWC. Voltage variations between the sensors allow the PCM to determine the
performance of the TWC catalyst. When the TWC catalyst becomes less effective in promoting chemical reactions, the catalyst's capacity to store and
release oxygen is generally degraded. The OBD 2 catalyst monitor diagnostic is based on a correlation between the conversion efficiency of the TWC
catalyst and the oxygen storage capacity of the catalyst. A good catalyst, e.g., 95 percent hydrocarbon conversion efficiency, will show a relatively
flat output voltage on the post-catalyst sensor, HO2S 2. A degraded catalyst, 65 percent hydrocarbon conversion, will show greatly increased activity
in the output voltage from the post catalyst HO2S.
The post-catalyst HO2S is used to measure the oxygen storage and release capacity of the catalyst in the TWC. A high oxygen storage capacity
indicates a good catalyst. A low oxygen storage capacity indicates a failing catalyst. The TWC and the HO2S 2 must be at operating temperature in
order to achieve the correct oxygen sensor voltages, like those shown in the post-catalyst HO2S Outputs graphic.
The catalyst monitor diagnostic is sensitive to the following conditions:
