Part 2

On-Board Refueling Vapor Recovery (ORVR) Evaporative Emission (EVAP) System

The basic elements forming the ORVR system are as follows:
- The fuel filler pipe forms a seal to prevent vapors from escaping the fuel tank while liquid is entering the fuel tank. Liquid in the one-inch diameter tube blocks vapors from rushing back up the fuel filler pipe.
- The fill limiting vent valve (FLVV) controls the flow of vapors out of the fuel tank. The valve closes when the liquid level reaches a height associated with fuel tank usable capacity. The valve accomplishes the following:
- Limits the total amount of fuel that can be dispensed into the fuel tank.
- Prevents liquid gasoline from exiting the fuel tank when submerged, as well as when tipped well beyond a horizontal plane as part of the vehicle rollover protection in road accidents.
- Minimizes vapor flow resistance during anticipated refueling conditions.
- Fuel vapor tubing connects the FLW to the EVAP canister. This routes the fuel tank vapors, displaced by the incoming liquid, to the EVAP canister.
- A check valve in the filling system prevents liquid from rushing back up to the fuel filler pipe during the liquid flow variations associated with the filler nozzle shut-off.

Between refueling events, the EVAP canister is purged with fresh air so that it may be used to again store vapors accumulated during engine soaks or subsequent refueling events. The vapors drawn off of the carbon in the EVAP canister are consumed by the engine.

Exhaust Gas Recirculation (EGR) System Monitor
The electric or stepper" motor EGR system monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Input from the ECT, IAT, TP, CKP, MAF and MAP sensors is required to activate the EGR System Monitor. Once activated, the EGR system monitor will perform each of the tests described below during the engine modes and conditions indicated. Some of the EGR system monitor tests are also performed during on demand self test.

The electric EGR (EEGR) monitor consists of an electrical and functional test that checks the stepper motor and EEGR system for proper flow. The PCM controls the EEGR valve by commanding from 0 to 52 discrete increments or "steps" to get the value from fully closed to fully open. The stepper motor electrical test is a continuous check of the four electric stepper motor coils and circuits to the PCM. A malfunction is indicated if an open circuit, short to power or short to ground has occurred in one or more of the stepper motor coils or circuits for a calibrated period of time. If a malfunction has been detected, the EEGR system will be disabled, setting the key on, engine running (KOER) and continuous DTC P0403. Additional monitoring will be suspended for the remainder of the drive cycle, or until the next engine startup.

After the vehicle has warmed up and normal EEGR flow rates are being commanded by the PCM, the EEGR flow check is performed. The flow test is performed once per drive cycle when a minimum amount of exhaust gas is requested and the remaining entry conditions required to initiate the test are satisfied. If a malfunction is detected, the EEGR system as well as the EEGR monitor is disabled until the next engine startup.

The EEGR flow test is done by observing the behavior of two different values: MAP - the analog MAP sensor reading, and inferred MAP - calculated from the mass air flow sensor, throttle position, and rpm. During normal, steady-state operating conditions, EEGR is intrusively commanded ON to a specified percentage. Then, the EEGR is commanded OFF. If the EEGR system is working properly, there is a significant difference in both the observed and the calculated values of MAP, between the EGR-ON and the EGR-OFF states. When flow test entry conditions have been satisfied, EEGR is commanded to flow at a calibrated test rate (about 10%). At this time, the value of MAP is recorded (EGR-ON MAP). The value of inferred MAP EGR-ON IMAP is also recorded. Next the EEGR is commanded off (0%). Again, the value of MAP is recorded (EGR-OFF MAP) The value of EGR-OFF IMAP is also recorded. Typically, seven such ON/OFF samples are taken. After all the samples have been taken, the average EGR-ON MAP, EGR-ON IMAP, EGR-OFF MAP and EGR-OFF IMAP values are stored. Next, the difference between the EGR-ON and EGR-OFF value is calculated:
- MAP-delta = EGR-ON MAP-EGR-OFF MAP (analog MAP)
- IMAP-delta = EGR-ON IMAP-EGR-OFF IMAP (inferred MAP)

If the sum of MAP-delta and IMAP-delta exceeds a maximum threshold or falls below a minimum threshold, DTC P0400 (high or low flow malfunction) is registered. As an additional check, if the EGR-ON MAP exceeds a maximum threshold (BARO, a calibrated value), DTC P0400 (low flow) is set. This check is performed to detect reduced EGR flow on systems where the MAP pickup point is not located in the intake manifold, but is located just upstream of the EEGR valve in the EEGR delivery tube.

NOTE: BARO is inferred at engine startup using the KOEO MAP sensor reading. It is updated during high, part-throttle or high rpm engine operation.

If the inferred ambient temperature is less than -7°C (20°F), greater than 54°C (130°F), or the altitude is greater than 8,000 feet (BARO less than 22.5 in-Hg), the EEGR flow test cannot be reliably done. In these conditions, the EEGR flow test is suspended and a timer starts to accumulate the time in these conditions. When the vehicle leaves these extreme conditions, the timer starts decrementing, and if conditions permit, will attempt to complete the EGR flow monitor. If the timer reaches 500 seconds, the EEGR flow test is disabled for the remainder of the current driving cycle and the EGR Monitor will be set to a "ready" condition. A DTC of P1408, like the P0400, will indicate a EGR flow failure (outside the minimum or maximum limits) but is only set during the KOER self test. The P0400 and P0403 are MIL codes. P1408 is a non-MIL code.

Fuel System Monitor
The fuel system monitor is an on-board strategy designed to monitor the fuel trim system. The fuel control system uses fuel trim tables stored in the PCMs keep alive random access memory (RAM) to compensate for variability in fuel system components due to normal wear and again. Fuel trim tables are based on engine rpm and engine load. During closed-loop fuel control, the fuel trim strategy learns the corrections needed to correct a biased rich or lean fuel system. The correction is stored in the fuel trim tables. The fuel trim has two means of adapting; a long term fuel trim and a short term fuel trim. Long term relies on the fuel trim tables and short term refers to the desired air/fuel ratio parameter "LAMBSE." LAMBSE is calculated by the PCM from H02S inputs and helps maintain a 14.7:1 air/fuel ratio during closed-loop operation. Short term fuel trim and long term fuel trim work together. If the H02S indicates the engine is running rich, the PCM will correct the rich condition by moving short term fuel trim in the negative range (less fuel to correct for a rich combustion). If after a certain amount of time the short term fuel trim is still compensating for a rich condition, the PCM learns this and moves the long term fuel trim into the negative range to compensate and allows short term fuel trim to return to a value near 0%. Input from the ECT, IAT, and MAF sensors is required to activate the fuel trim system, which in turn activates the fuel system monitor. Once activated, the fuel system monitor looks for the fuel trim tables to reach the adaptive clip and LAMBSE to exceed a calibrated limit. The fuel system monitor will store the appropriate DTC when a fault is detected as described below.
1. The heated oxygen sensor (H02S) detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating air / fuel ratio.
2. A correction factor is added to the fuel injector pulse width calculation according to the long and short term fuel trims as needed to compensate for variations in the fuel system.
3. When deviation in the parameter LAMBSE increases, air / fuel control suffers and emissions increase. When LAMBSE exceeds a calibrated limit and the fuel trim table has clipped, the fuel system monitor sets a DTC as follows:
- The DTCs associated with the monitor detecting a lean shift in fuel system operation are DTCs P0171 and P0174.
- The DTCs associated with the monitor detecting a rich shift in fuel system operation are DTCs P0172 and P0175.

4. The MIL is activated after a fault is detected on two consecutive drive cycles.

Typical Fuel System Monitor Entry Conditions:
- RPM range between idle and 4,000 rpm.
- Air mass range greater than 0.75 lb/min.
- Purge duty cycle of 0%.

Typical Fuel Monitor Malfunction Thresholds:
- Lean Malfunction: LTFT > 25%, STFT > 5%.
- Rich Malfunction: LTFT < 25%, STFT < 10%.

Heated Oxygen Sensor (H02S) Monitor
The H02S monitor is an on-board strategy designed to monitor the H02S sensors for a malfunction or deterioration which can affect emissions. The fuel control or stream 1 H02S sensors are checked for proper output voltage and response rate (the time it takes to switch from lean to rich and vice versa). Stream 2 H02S sensors used for catalyst monitor, and Stream 1 H02S sensors used for fore-aft oxygen sensor (FAOS) control are also monitored for proper output voltage. The fuel system monitor and misfire detection monitor must also have completed successfully before the H02S monitor is enabled.
1. The H02S sensor senses the oxygen content in the exhaust flow and outputs a voltage between zero and 1.0 volt. Lean of stoichiometric (air / fuel ratio of approximately 14.7:1), the H02S will generate a voltage between zero and 0.45 volts. Rich of stoichiometric, the H02S will generate a voltage between 0.45 and 1.0 volt. The H02S monitor evaluates the stream 1 (fuel control), stream 2 (catalyst monitor) and the Stream 3 H02S (FAOS control) for proper function.
2. Once the H02S monitor is enabled, the stream 1 H02S signal voltage amplitude and response frequency are checked. Excessive voltage is determined by comparing the H02S signal voltage to a maximum calibratable threshold voltage. A fixed frequency closed loop fuel control routine is executed and the stream 1 H02S voltage amplitude and output response frequency are observed. A sample of the stream 1 H02S signal is evaluated to determine if the sensor is capable of switching or has a slow response rate. An H02S heater circuit fault is determined by turning the heater on and off and looking for a corresponding change in the output state monitor (OSM) and by measuring the current going through the heater circuit. Since the 2002 model year, vehicles will monitor the H02S signal for a high voltage in excess of 1.5 volts.
3. The MIL is activated after a fault is detected on two consecutive drive cycles.

The H02S Monitor DTCs can be categorized as follows:
- H02S signal circuit malfunction - P0131, P0136, P0151, P0156.
- H02S slow response rate - P0133, P0153.
- H02S circuit high voltage -P0132, P0138, P0144, P0152, P0158, P0164.
- H02S heater circuit malfunction - P0135, P0141, P0155, P0161, P0147, P0167.
- H02S heater current malfunction - P0053, P0054, P0055, P0059, P0060, P0061.
- Downstream H02S not running in on-demand self test-P1127.
- Swapped H02S connectors - P0040, P0041, P1128, P1129, P2278.
- H02S lack of switching - P1131, P1132, P1151, P1152, P2195, P2196, P2197, P2198.
- H02S lack of switching (sensor indicates lean) - P1137, P1157, P2270, P2272, P2274, P2276.
- H02S lack of switching (sensor indicates rich) - P1138, P1158, P2271, P2273, P2275, P2277.

Misfire Detection Monitor
The misfire detection monitor is an on-board strategy designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause. The misfire detection monitor will be enabled only when certain base engine conditions are first satisfied. Input from the ECT, MAF and CKP sensors is required to enable the monitor. The misfire detection monitor is also performed during on demand self-test.
1. The PCM synchronized ignition spark is based on information received from the CKP sensor. The CKP signal generated is also the main input used in determining cylinder misfire.
2. The input signal generated by the CKP sensor is derived by sensing the passage of teeth from the crankshaft position wheel mounted on the end of the crankshaft.
3. The input signal to the PCM is then used to calculate the time between CKP edges and also crankshaft rotational velocity and acceleration. By comparing the accelerations of each cylinder event, the power loss of each cylinder is determined. When the power loss of a particular cylinder is sufficiently less than a calibrated value and other criteria is met, then the suspect cylinder is determined to have misfired.
4. Misfire type A:
- Upon detection of a misfire type A (200 revolutions) which would cause catalyst damage, the MIL will blink once per second during the actual misfire, and a DTC will be stored.

5. Misfire type B:
- Upon detection of a misfire type B (1000 revolutions) which will exceed the emissions threshold or cause a vehicle to fail an inspection and maintenance tailpipe emissions test, the MIL will illuminate and a DTC will be stored.
- The DTC associated with multiple cylinder misfire for a Type A or Type B misfire is DTC P0300.
- The DTCs associated with an individual cylinder misfire for a Type A or Type B misfire are DTCs P0301, P0302, P0303, P0304, P0305, and P0306.

Malfunction Indicator Lamp (MIL)
The MIL alerts the driver that the PCM has detected an OBD II emission-related component or system fault. When this occurs, a DTC will be set.
- The MIL is located on the instrument cluster and is labeled CHECK ENGINE.
- Power is supplied to the MIL whenever the ignition switch is in the ON or START position.
- The MIL will remain on in the ON / START mode as a bulb check during the instrument cluster prove out for approximately 4 seconds.
- If the MIL remains on after the bulb check:
- The PCM illuminates the MIL for an emission-related concern and a DTC will be present.
- The instrument cluster will illuminate the MIL if the PCM does not send a control message to the instrument cluster.
- The PCM is operating in the hardware limited operation strategy (HLOS).
- The MIL circuit is shorted to ground.

- If the MIL remains off (during the bulb check):
- bulb is damaged
- MIL circuit is open

- To turn off the MIL after a repair, a reset command from the IDS or equivalent tester must be sent, or three consecutive drive cycles must be completed without a fault.
- For any MIL concern, See SYMPTOM TROUBLESHOOTING CHART - ENGINE DRIVEABILITY. Symptom Troubleshooting Chart - Engine Driveability
- If the MIL blinks at a steady rate, a severe misfire condition could possibly exist.
- If the MIL blinks erratically, an intermittent open B+ to the bulb or an intermittent short to ground in the MIL circuit exist. Also, the PCM can reset while cranking if battery voltage is low.