Task Manager

Task Manager
The PCM is responsible for efficiently coordinating the operation of all the emissions-related components. The PCM is also responsible for determining if the diagnostic systems are operating properly. The software designed to carry out these responsibilities is called the Task Manager.

The Task Manager determines which tests happen when and which functions occur when. Many of the diagnostic steps required by OBD II must be performed under specific operating conditions. The Task Manager software organizes and prioritizes the diagnostic procedures. The job of the Task Manager is to determine if conditions are appropriate for tests to be run, monitor the parameters for a trip for each test, and record the results of the test. Following are the responsibilities of the Task Manager software:
- Test Sequence
- MIL Illumination
- Diagnostic Trouble Codes (DTCs)
- Trip Indicator
- Freeze Frame Data Storage
- Similar Conditions Window

Test Sequence
In many instances, emissions systems must fail diagnostic tests more than once before the PCM illuminates the MIL. These tests are know as "two trip monitors." Other tests that turn the MIL lamp on after a single failure are known as "one trip monitors." A trip is defined as "start the vehicle and operate it to meet the criteria necessary to run the given monitor." Many of the diagnostic tests must be performed under certain operating conditions. However, there are times when tests cannot be run because another test is in progress (Conflict), another test has failed (Pending) or the Task Manager has set a fault that may cause a failure of the test (Suspend).

- Pending
Under some situations, the Task Manager will not run a monitor if the MIL is illuminated and a fault is stored from another monitor. In these situations, the Task Manager postpones monitors Pending resolution of the original fault. The Task Manager does not run the test until the problem is remedied. For example, when the MIL is illuminated for an Oxygen Sensor fault, the Task Manager does not run the Catalyst Monitor until the Oxygen Sensor fault is remedied. Since the Catalyst Monitor is based on signals from the Oxygen Sensor, running the test would produce inaccurate results.

- Conflict
There are situations when the Task Manager does not run a test if another monitor is in progress. In these situations, the effects of another monitor running could result in an erroneous failure. If this Conflict is present, the monitor is not run until the conflicting condition passes. Most likely the monitor will run later after the conflicting monitor has passed. For example, if the Fuel System Monitor is in progress, the Task Manager does not run the EGR Monitor. Since both tests monitor changes in air/fuel ratio and adaptive fuel compensation, the monitors will conflict with each other.

- Suspend
Occasionally the Task Manager may not allow a two trip fault to mature. The Task Manager will Suspend the maturing of a fault if a condition exists that may induce an erroneous failure. This prevents illuminating the MIL for the wrong fault and allows more precise diagnosis.For example, if the PCM is storing a one trip fault for the Oxygen Sensor and the EGR monitor, the Task Manager may still run the EGR Monitor but will suspend the results until the Oxygen Sensor Monitor either passes or fails. At that point the Task Manager can determine if the EGR system is actually failing or if an Oxygen Sensor is failing.

MIL illumination
The PCM Task Manager carries out the illumination of the MIL. The Task Manager triggers MIL illumination upon test failure, depending on monitor failure criteria.

The Task Manager Screen shows both a Requested MIL state and an Actual MIL state. When the MIL is illuminated upon completion of a test for a third trip, the Requested MIL state changes to OFF. However, the MIL remains illuminated until the next key cycle. During the key cycle for the third good trip, the Requested MIL state is OFF, while the Actual MIL state is ON. After the next key cycle, the MIL is not illuminated and both MIL states read OFF.

Diagnostic Trouble Codes (DTCs)
With OBD II, different DTC faults have different priorities according to regulations. As a result, the priorities determine MIL illumination and DTC erasure. DTCs are entered according to individual priority. DTCs with a higher priority overwrite lower priority DTCs.

Priorities
- Priority 0 - Non-emissions related trouble codes
- Priority 1 - One trip failure of a two trip fault for non-fuel system and non-misfire.
- Priority 2 - One trip failure of a two trip fault for fuel system (rich/lean) or misfire.
- Priority 3 - Two trip failure for a non-fuel system and non-misfire or matured one trip comprehensive component fault.
- Priority 4 - Two trip failure or matured fault for fuel system (rich/lean) and misfire or one trip catalyst damaging misfire.

Non-emissions related failures have no priority. One trip failures of two trip faults have low priority. Two trip failures or matured faults have higher priority. One and two trip failures of fuel system and misfire monitor take precedence over non-fuel system and non-misfire failures.

DTC Self Erasure
With one trip components or systems, the MIL is illuminated upon test failure and DTCs are stored.

Two trip monitors are components requiring failure in two consecutive trips for MIL illumination. Upon failure of the first test, the Task Manager enters a maturing code. If the component fails the test for a second time the code matures and a DTC is set.

After three good trips the MIL is extinguished and the Task Manager automatically switches the trip counter to a warm-up cycle counter. DTCs are automatically erased following 40 warm-up cycles if the component does not fail again. For misfire and fuel system monitors, the component must pass the test under a Similar Conditions Window in order to record a good trip. A Similar Conditions Window is when engine RPM is within ±375 rpm and load is within ±10% of when the fault occurred.

NOTE: It is important to understand that a component does not have to fail under a similar window of operation to mature. It must pass the test under a Similar Conditions Window when it failed to record a Good Trip for DTC erasure for misfire and fuel system monitors.

DTCs can be erased anytime with a DRB III(R). Erasing the DTC with the DRB III(R) erases all OBD II information. The DRB III(R) automatically displays a warning that erasing the DTC will also erase all OBD II monitor data. This includes all counter information for warm-up cycles, trips and Freeze Frame.

Freeze Frame Data Storage
Once a failure occurs, the Task Manager records several engine operating conditions and stores it in a Freeze Frame. The Freeze Frame is considered one frame of information taken by an onboard data recorder. When a fault occurs, the PCM stores the input data from various sensors so that technicians can determine under what vehicle operating conditions the failure occurred.

The data stored in Freeze Frame is usually recorded when a system fails the first time for two trip faults. Freeze Frame data will only be overwritten by a different fault with a higher priority.

NOTE: Erasing DTCs, either with the DRB III(R) or by disconnecting the battery, also clears all Freeze Frame data.

Non-Monitored Circuits
The PCM does not monitor all circuits, systems and conditions that could have malfunctions causing driveability problems. However, malfunctions in these systems may cause the PCM to store diagnostic trouble codes for other systems or components. For example, a fuel pressure problem will not register a fault directly but could cause a rich/lean condition or misfire. This could cause the PCM to store an oxygen sensor or misfire diagnostic trouble code.

The major non-monitored circuits are listed below along with examples of failure modes that do not directly cause the PCM to set a DTC, but instead for a system that is monitored.

FUEL PRESSURE
The fuel pressure regulator controls fuel system pressure. The PCM cannot detect a clogged fuel pump inlet filter, clogged in-line fuel filter, or a pinched fuel supply or return line. However, these could result in a rich or lean condition causing the PCM to store an oxygen sensor, fuel system, or misfire diagnostic trouble code.

SECONDARY IGNITION CIRCUIT
The PCM cannot detect an inoperative ignition coil, fouled or worn spark plugs, ignition cross firing, or open spark plug cables. The misfire will, however, increase the oxygen content in the exhaust, deceiving the PCM into thinking the fuel system is too lean. Also see misfire detection.

CYLINDER COMPRESSION
The PCM cannot detect uneven, low, or high engine cylinder compression. Low compression lowers O2 content in the exhaust, leading to a fuel system, oxygen sensor or misfire detection fault.

EXHAUST SYSTEM
The PCM cannot detect a plugged, restricted or leaking exhaust system. It may set an EGR, Fuel system or O2S fault.

FUEL INJECTOR MECHANICAL MALFUNCTIONS
The PCM cannot determine if a fuel injector is clogged, the needle is sticking or if the wrong injector is installed. However, these could result in a rich or lean condition causing the PCM to store a diagnostic trouble code for either misfire, an oxygen sensor or the fuel system.

EXCESSIVE OIL CONSUMPTION
Although the PCM monitors engine exhaust oxygen content when the system is in closed loop, it cannot determine excessive oil consumption.


THROTTLE BODY AIR FLOW
The PCM cannot detect a clogged or restricted air cleaner inlet or filter element.

VACUUM ASSIST
The PCM cannot detect leaks or restrictions in the vacuum circuits of vacuum assisted engine control system devices or vacuum assisted accessories. However, these could cause the PCM to store a MAP sensor diagnostic trouble code and cause a high idle condition.

PCM SYSTEM GROUND
The PCM cannot determine a poor system ground. However, one or more diagnostic trouble codes may be generated as a result of this condition.

PCM CONNECTOR ENGAGEMENT
The PCM may not be able to determine spread or damaged connector pins. However, it might store diagnostic trouble codes as a result of pins not making good contact.

High and Low Limits
The PCM compares input signal voltages from each input device with established high and low limits for the device. If the input voltage is not within limits and other criteria are met, the PCM stores a diagnostic trouble code in memory. Other diagnostic trouble code criteria might include engine RPM limits or input voltages from other sensors or switches that must be present before verifying a diagnostic trouble code condition.