Monitored Systems

MONITORED SYSTEMS
There are new electronic circuit monitors that check fuel, emission, engine and ignition performance. These monitors use information from various sensor circuits to indicate the overall operation of the fuel, engine, ignition and emission systems and thus the emissions performance of the vehicle.

The fuel, engine, ignition and emission systems monitors do not indicate a specific component problem. They do indicate that there is an implied problem within one of the systems and that a specific problem must be diagnosed.

If any of these monitors detect a problem affecting vehicle emissions, the Malfunction Indicator (Check Engine) Lamp will be illuminated. These monitors generate Diagnostic Trouble Codes that can be displayed with the check engine lamp or a scan tool.

The following is a list of the monitored systems:
- EGR Monitor
- Misfire Monitor
- Fuel System Monitor
- Evaporative Emissions Monitor

Following is a description of each system monitor, and its DTC.
Refer to the appropriate Powertrain Diagnostics Procedures for diagnostic procedures.

EGR MONITOR
The Powertrain Control Module (PCM) performs an on-board diagnostic check of the EGR system.

The EGR system consists of two main components: a vacuum solenoid back pressure transducer and a vacuum operated valve. The EGR monitor is used to test whether the EGR system is operating within specifications. The diagnostic check activates only during selected engine/driving conditions. When the conditions are met, the EGR is turned OFF (solenoid energized) and the O2S compensation control is monitored. Turning OFF the EGR shifts the air fuel (A/F) ratio in the lean direction. Oxygen sensor voltage then indicates increased oxygen in the exhaust. Consequently, Short Term Compensation shifts to rich (increased injector pulse width). By monitoring the shift, the PCM can indirectly monitor the EGR system. While this test does not directly measure the operation of the EGR system, it can be inferred from the shift in the O2S data whether the EGR system is operating correctly. Because the O2S is being used, the O2S test must pass its test before the EGR test.

Enabling Conditions
- Engine Temperature
- Engine Run Time
- Engine RPM
- MAP Sensor
- TPS
- Vehicle Speed
- Short Term Compensation

Pending Conditions
The EGR Monitor does not run when any of the following example faults have illuminated the MIL:
- Misfire
- Oxygen Sensor Monitor
- Oxygen Sensor Heater Monitor
- Fuel System Rich/Lean
- Limp in for MAP, TPS or ECT
- Vehicle Speed Sensor
- Cam or Crank Sensor
- EGR Electrical
- EVAP Electrical
- Fuel Injector
- Ignition Coil
- Idle Speed
- Engine Coolant Temperature (ECT)
- MAP Sensor
- Intake Air Temperature (IAT)

Conflict Conditions
The EGR Monitor typically does not run if any of the following conditions are present:
- Fuel System Monitor
- Purge Monitor
- Catalyst Monitor
- Low Fuel Level
- High Altitude
- Low Ambient Air Temperature

The EGR Monitor does not run if any of the following example DTCs are present:
- Misfire Monitor, Priority 2
- Upstream Oxygen Sensor Heater, Priority 1
- Fuel System Monitor, Priority 2
- Oxygen Sensor Monitor, Priority 1

MISFIRE MONITOR
Excessive engine misfire results in increased catalyst temperature and causes an increase in HC emissions. Severe misfires could cause catalyst damage. To prevent catalytic convertor damage, the PCM monitors engine misfire.

The Powertrain Control Module (PCM) monitors for misfire during most engine operating conditions (positive torque) by looking at changes in the crankshaft speed. If a misfire occurs the speed of the crankshaft will vary more than normal.

OBD II regulations for misfire monitoring require two different tests for misfire. The first is a Catalyst Damage level of misfire test. The second is for emissions greater than 1.5 times the Federal Tailpipe (FTP) standards. The tests are monitored by two different counters. These counters are:
- 200 revolution increments for immediate catalyst damage
- 1000 revolution increments for emissions violation and Inspection/Maintenance (I/M) test failure

NOTE: The percent of misfire for malfunction criteria varies due to RPM and load. As the engine speed increases or load decreases, the effects of a misfire diminishes due to crankshaft momentum. Failure percentages also vary from engine to engine.

Monitor Operation
The PCM utilizes the Crankshaft Speed Fluctuation method to monitor for misfire. The misfire monitor utilizes a crankshaft position sensor to determine engine RPM. The sensor can detect slight variations in engine speed due to misfire. Misfire is continuously monitored once the enabling conditions are met.

Once enabling conditions are met, the PCM counts the number of misfires in every 200 revolutions of the crankshaft. If, during five 200 counters, the misfire percentage exceeds a predetermined value, a maturing code is set and a Freeze Frame is entered. Freeze Frame data is recorded during the last 200 revolutions of the 1000 revolution period. A failure on the second consecutive trip matures the code and a DTC is set.

If misfire continues during the initial trip, the MIL is not illuminated. However, the MIL flashes when the misfire percentage exceeds the malfunction percentage, in any 200 revolution period, that would cause permanent catalyst damage. This is a one trip monitor. If misfire reaches a point in which catalyst damage is likely to occur, the MIL flashes and a DTC is stored in a Freeze Frame. The engine defaults to open loop operation to prevent increased fuel flow to the cylinders. Once misfire is below the predetermined percentage, the MIL stops flashing but remains illuminated.

The 1000 revolution counters are two trip monitors. As with the fuel system monitor, Freeze Frame data is from the original fault, and MIL extinguishing requires the monitor to pass under similar conditions.

The Adaptive Numerator
The Misfire Monitor takes into account component wear, sensor fatigue and machining tolerances. The PCM compares the crankshaft in the vehicle to data on an ideal crank and uses this as a basis to determine variance. To do this, the crankshaft sensor monitors the reference notches in the crank. The PCM uses the first signal set as a point of reference. It then measures where the second set of signals is, compared to where engineering data has determined it should be. This variance is the Adaptive Numerator. The monitor will not run if the numerator is not set.

If the Adaptive Numerator is equal to the default value, the adaptive Numerator has not been learned and the Misfire Monitor does not run. If the Adaptive Numerator exceeds its limits, the PCM sets a DTC for Adaptive Numerator and illuminates the MIL.

RPM Error
The PCM also checks the machining tolerances for each group of slots. By monitoring the speed of the crank from the first slot to the last slot in a group, the PCM can calculate engine RPM. The variance between groups of slots is know as the RPM error. In order for the PCM to run the Misfire Monitor, RPM error must be less than approximately 5%.

Enabling Conditions
The following conditions must be met before the PCM runs the Misfire Monitor:
- RPM
- Engine Coolant Temperature (ECT)
- Barometric Pressure (MAP) Fuel level
- Ambient air Temperature

Pending Conditions
The Misfire Monitor does not run when the MIL is illuminated for any of the following:
- Limp in mode for
- MAP
- TPS
- Crankshaft Sensor
- Engine Coolant Temperature Sensor
- Speed Sensor DTC
- EGR Electrical
- EVAP Electrical
- Idle Speed Faults
- Intake Air Temperature
- Oxygen Sensor Monitor
- Oxygen Sensor Electrical

Conflict Conditions
If any of the following conditions conflict with the Misfire Monitor, the monitor will not run:
- Low fuel level
- MAP voltage rapidly changing
- Severe engine decel
- TPS toggling OPEN/CLOSED
- Engine rpm too low (rpm levels vary by vehicle)
- Engine rpm too high (rpm levels vary by vehicle)
- Full Lean or Decel Fuel Shut-off
- Cold start

FUEL SYSTEM MONITOR
To comply with clean air regulations, vehicles are equipped with catalytic converters. These converters reduce the emission of hydrocarbons, oxides of nitrogen and carbon monoxide. The catalyst works best when the air fuel (A/F) ratio is at or near the optimum of 14.7 to 1.

The PCM is programmed to maintain the optimum air/fuel ratio of 14..7 to 1. This is done by making short term corrections in the fuel injector pulse width based on the O2S output. The programmed memory acts as a self calibration tool that the engine controller uses to compensate for variations in engine specifications, sensor tolerances and engine fatigue over the life span of the engine. By monitoring the actual air-fuel ratio with the O2S (short term) and multiplying that with the program long-term (adaptive) memory and comparing that to the limit, it can be determined whether it will pass an emissions test. If a malfunction occurs such that the PCM cannot maintain the optimum A/F ratio, then the MIL will be illuminated.

Monitor Operation
Fuel systems monitors do not have a pre-test because they are continuously running monitors. Therefore, the PCM constantly monitors Short Term Compensation and Long Term Adaptive memory.

Lean: If at anytime during a lean engine operation, short term compensation multiplied by long term adaptive exceeds a certain percentage for an extended period, the PCM sets a Fuel System Lean Fault for that trip and a Freeze Frame is entered.

Rich: If at anytime during a rich operation, Short Term Compensation multiplied by Long Term Adaptive is less than a predetermined value, the PCM checks the Purge Free Cells.

Purge Free Cells are values placed in Adaptive Memory cells when the EVAP Purge Solenoid is OFF. Two, three or four Purge Free cells are used. One corresponds to an Adaptive Memory cell at idle, the other to a cell that is off-idle. For example, if a Purge Free cell is labeled PFC1, it would hold the value for Adaptive Memory cell C1 under non-purge conditions.

If all Purge Free Cells are less than a certain percentage, and the Adaptive Memory factor is less than a certain percentage, the PCM sets a Fuel System Rich fault for that trip and a Freeze Frame is entered.

The Fuel Monitor is a two trip monitor. The PCM records engine data in Freeze Frame upon setting of the first fault, or maturing code. When the fuel monitor fails on a second consecutive trip, the code is matured and the MIL is illuminated. The stored Freeze Frame data is still from the first fault.

In order for the PCM to extinguish the MIL, the Fuel Monitor must pass in a Similar Condition Window. The similar conditions relate to rpm and load. The engine must be within a predetermined percentage of both rpm and load when the monitor runs to count a good trip. As with all DTCs, three good trips are required to extinguish the MIL and 40 warm up cycles are required to erase the DTC. If the engine does not run in a Similar Conditions Window, the Task Manager extinguishes the MIL after 80 good trips.

Enabling Conditions
The following conditions must be met to operate the fuel control monitor:
- PCM not in fuel crank mode (engine running)
- PCM in Closed Loop fuel control
- Fuel system updating Long Term Adaptive
- Fuel level above 15% of capacity
- Fuel level below 85% of capacity

Pending Conditions
The Fuel Control Monitor does not operate if the MIL is illuminated for any of the following:
- Misfire Monitor
- Upstream O2S
- EVAP Purge Solenoid Electrical PCM Self Test Fault
- Camshaft or Crankshaft Position Sensor
- Fuel Injectors
- Ignition Coil Primary
- Throttle Position (TPS) Sensor
- Engine Coolant Temperature (ECT) Sensor
- Manifold Absolute Pressure (MAP) Sensor
- Idle Air Control (IAC)
- 5 volt Output Too Low
- EGR Monitor
- EGR Solenoid Circuit
- Vehicle Speed Sensor
- Oxygen Sensor Monitor
- Oxygen Sensor Heater Monitor
- Oxygen Sensor Electrical
- Idle Speed Rationality
- Intake Air Temperature

Suspend
The Task Manager will suspend maturing a Fuel System fault if any of the following are present:
- Oxygen Sensor Response, Priority 1
- O2 Heater Priority 1
- Misfire Monitor, Priority 2

EVAPORATIVE EMISSIONS MONITOR - LEAK DETECTION PUMP
The leak detection assembly incorporates two primary functions: it must detect a leak in the evaporative system and seal the evaporative system so the leak detection test can be run.

The primary components within the assembly are:
A three port solenoid that activates both of the functions listed above; a pump which contains a switch, two check valves and a spring/diaphragm, a canister vent valve (CVV) seal which contains a spring loaded vent seal valve.

Immediately after a cold start, between predetermined temperature thresholds limits, the three port solenoid is briefly energized. This initializes the pump by drawing air into the pump cavity and also closes the vent seal. During non test conditions the vent seal is held open by the pump diaphragm assembly which pushes it open at the full travel position. The vent seal will remain closed while the pump is cycling due to the reed switch triggering of the three port solenoid that prevents the diaphragm assembly from reaching full travel. After the brief initialization period, the solenoid is de-energized allowing atmospheric pressure to enter the pump cavity, thus permitting the spring to drive the diaphragm which forces air out of the pump cavity and into the vent system. When the solenoid is energized and de energized, the cycle is repeated creating flow in typical diaphragm pump fashion. The pump is controlled in 2 modes:

Pump Mode: The pump is cycled at a fixed rate to achieve a rapid pressure build in order to shorten the overall test length.

Test Mode: The solenoid is energized with a fixed duration pulse. Subsequent fixed pulses occur when the diaphragm reaches the Switch closure point.

The spring in the pump is set so that the system will achieve an equalized pressure of about 7.5 "H2O. The cycle rate of pump strokes is quite rapid as the system begins to pump up to this pressure. As the pressure increases, the cycle rate starts to drop off. If there is no leak in the system, the pump would eventually stop pumping at the equalized pressure. If there is a leak, it will continue to pump at a rate representative of the flow characteristic of the size of the leak. From this information we can determine if the leak is larger than the required detection limit (currently set at 0.040" orifice by CARB). If a leak is revealed during the leak test portion of the test, the test is terminated at the end of the test mode and no further system checks will be performed.

After passing the leak detection phase of the test, system pressure is maintained by turning on the LDP's solenoid until the purge system is activated. Purge activation in effect creates a leak. The cycle rate is again interrogated and when it increases due to the flow through the purge system, the leak check portion of the diagnostic is complete.

The canister vent valve will unseal the system after completion of the test sequence as the pump diaphragm assembly moves to the full travel position.

Evaporative system functionality will be verified by using the stricter evap purge flow monitor. At an appropriate warm idle the LDP will be energized to seal the canister vent. The purge flow will be clocked up from some small value in an attempt to see a shift in the O2 control system. If fuel vapor, indicated by a shift in the O2 control, is present the test is passed. If not, it is assumed that the purge system is not functioning in some respect. The LDP is again turned OFF and the test is ended.

Enabling Conditions for Systems with LDP
- Ambient Air Temperature
- Barometric Pressure
- Fuel level
- Engine Temperature
- No stalling
- Battery voltage

EVAPORATIVE EMISSIONS MONITOR - NON-LDP VEHICLES
On a vehicle without an EVAP leak detection pump system, changes in short term memory and movement in target IAC at idle or idle speed change, are used to monitor the system. There are two stages for this test.

Stage One: Stage one is a non-intrusive test. The PCM compares adaptive memory values between purge and purge-free cells. The PCM uses these values to determine the amount of fuel vapors entering the system. If the difference between the cells exceeds a predetermined value, the test passes. If not, then the monitor advances to state two.

Stage Two: Once the enabling conditions are met, the PCM de-energizes the Duty Cycle Purge (DCP) solenoid. The PCM then waits until engine RPM, Short Term Compensation and Idle Air Control have all stabilized. Once stable, the PCM increments the DCP solenoid cycle rate approximately 6% every 8 engine revolutions. If during the test any one of three conditions occur before the DCP cycle reaches 100%, the EVAP system is considered to be operational and the test passes. These conditions are as follows:
- RPM rises by a predetermined amount
- Short Term drops by a predetermined amount
- Idle Air Control closes by a predetermined amount

When none of the previous conditions occur, the test fails and the PCM increments a counter by one. when the PCM runs the test three times during a trip, and the counter has been incremented to three, the monitor fails and a Freeze Frame is stored.

Enabling Conditions (Stage Two)
The following conditions must be met to enable the EVAP Monitor (without LDP)
- Ambient Air Temperature
- Barometric Pressure
- Fuel level
- Engine Temperature
- Engine run time
- RPM stable
- MAP
- Generator, radiator fans, A/C clutch

Pending Conditions (With or Without LDP)
The EVAP Monitor is suspended and does not run, when the MIL is illuminated due to any of the following faults:
- Misfire
- Oxygen Sensor Monitor
- Fuel System Rich
- Fuel System Lean
- EGR Monitor
- MAP
- TPS
- ECT
- DCP Solenoid

Conflict Conditions (With or Without LDP)
The EVAP Monitor does not run if any of the following tests are in progress:any of the following tests are in progress:
- Catalyst
- EGR
- Fuel System
- Misfire