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Copy of OBD II Systems

OBD II System Monitors and Monitor Readiness
by

Devon Barkley

on 29 January 2013

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Transcript of Copy of OBD II Systems

By the magnificent Devon Barkley OBD II Systems and their monitoring System Monitors OBD II Purpose THE END Air Conditioning*
Catalyst Efficiency
Comprehensive Component Monitor (CCM) EGR System
Evaporative System (EVAP)
Fuel System (adaptive fuel system trim)
Heated Catalyst
Heated Oxygen Sensor
Misfire Detection
Positive Crankcase Ventilation*
Secondary Air Injection
Thermostat* Two types of monitors: Continuous The OBD II's main purpose is to protect the catalytic converters. The main ways that these can be damaged is through too much fuel delivery and ignition misfire.

Therefore, the continuous monitors are the fuel system, misfire, and comprehensive component monitors.

The other monitors are less critical and they run only when the conditions are exactly right Noncontinuous these monitors are monitors that are always running when their enabling criteria are met and the vehicle is being driven these monitors are only run when their individual enabling criteria are met, and the PCM does not
detect any conditions or malfunctions that would cause the test results to be inaccurate These monitors have a much more specific enabling criteria These monitors enabling criteria is much less detailed than noncontinuous monitors Trips and warm-up cycles Some major catalyst damaging faults can turn on the MIL in one trip.

However, most faults are two-trip logic type faults and while they may be seen with a scan tool after occuring on just one trip they will not turn on the MIL until the same fault is set on two individual trips

Some faults may also be cleared by the pcm after as few as three trips.Although others may require many more fault-free trips. The Monitors Fuel System Monitor
continuous monitor
requires more enabling criteria than misfire monitor
Enabling Criteria
Warm engine (above 160°F)
Engine Management System operating in Closed-Loop mode
Valid signals present from MAP, MAF, BARO, ECT, IAT, TPS, VSS, and RPM
Long-Term Fuel Trim data present
Short-Term Fuel Trim data present The Monitors Misfire Monitor:
Continuous monitor
This is because a severe misfire can damage the catalyst very quickly
Enabling criteria
Valid signals from MAP, MAF, ECT, VSS, and RPM
RPM within a specified range
ECT within a specified range
VSS within a specified range The Monitors The Monitors Comprehensive Component Monitor:
used to check for shorts, opens, and rationality between many inputs and outputs of the pcm
These include:
Inputs EVAP Switches
Knock Sensor
MAF
MAP
BARO
Clutch Switch
Transmission Range Selector
VSS
IAT
ECT
Cruise Control Command/Requests
RPM
CKP
CMP
Brake on/off switch Outputs EVAP Purge and Vent solenoids
IAC or ISC Position
Ignition spark advance
Torque Converter Clutch Solenoid
Automatic Transmission Shift Solenoids Oxygen sensor and Oxygen Sensor Heater Monitors
Most important monitor information that the pcm relies on
Continuous monitor once it meet the enabling criteria
Enabling Criteria
Engine temperature warm (usually above 120°F.)
Engine run time exceeds preprogrammed limit
Transmission is in specified gear or specified range is selected
TPS within specified range
EVAP is not purging
VSS has been within specified range for specified amount of time without interruption
The monitors Heated Catalyst and Catalyst Efficiency Monitor
this monitor usually runs once per trip
designed to see how well the converter is doing its job
Enabling Criteria
ECT at specified temperature (usually around 160°F, near complete warm-up)
TPS indicates off-idle (part throttle)
Engine operating in Closed Loop
RPM and MAP or MAF within their specified range The Monitors EGR (Exhaust Gas Recirculation) Monitor\
checked continuously for shorted and open circuits
Very exact measurement, prone to failure due to high temperature exposure
Enabling Criteria
Engine is warm (usually 180°F or more)
Engine has been running for a specied amount of time
RPM, MAP or MAF, and TPS are within a specified range
VSS is within a specified range.
part-throttle cruising conditions for the EGR monitor to run.
Short-term Fuel Trim (STFT) is within a specified range. The Monitors EVAP Monitor
tested to make sure that the fuel system is preventing gasoline vapors from evaporating into the air
Enabling Criteria
Engine running in Closed Loop
Oxygen Sensor Monitor has been run with passed results
ECT is 170°F or above
Transmission is in specified gear or selected range
TPS and RPM are within a specified range
The Monitors Secondary Air Injection or Air Injection
Reactor (AIR) Monitor
some vehicles equipped with OBD II still use this system to add oxygen to help the catalyst perform
passive test measures oxygen sensor readings during warm-up, when the PCM has the secondary air directed upstream, into the exhaust manifold
If passive test fails it may perform the active test
switches on the upstream air injection temporarily while in closed loop. Should send lean signal to the pcm with injection on
Enabling Criteria
Engine started and running in Open Loop
Successful switching of engine management system to Closed Loop
Valid upstream oxygen sensor(s) signal
Full transcript