Preliminary Checks
Before using this section you should have already performed "On-Board Diagnostic System Check".
Perform a thorough visual inspection. This inspection can often lead to correcting a problem without further checks and can save valuable time. Inspect for the following conditions
- Powertrain control module (PCM)/engine control module (ECM) grounds for being clean, tight, and in proper location.
- Vacuum hoses for splits, kinks, collapsing and proper connections as shown on Vehicle Emission Control Information label. Inspect thoroughly for any type of leak or restriction.
- Air leaks at throttle body mounting area and intake manifold sealing surfaces.
- Ignition wires for cracks, hardness, proper routing, and carbon tracking.
- Wiring for proper connections.
- Wiring for pinches or cuts.
Fuel System
Some intermittent driveability problems can be attributed to poor fuel quality. If a vehicle is occasionally running rough, stalling, or otherwise performing badly, ask customer about following fuel buying habits.
- Do they always buy from same source? If so, fuel quality problems can usually be discounted.
- Do they buy their fuel from whichever fuel station that is advertising lowest price? If so, check fuel tank for signs of debris, water, or other contamination.
IDLE LEARN PROCEDURE
Whenever battery cables, PCM/ECM, or PCM/ECM fuse is disconnected or replaced, the following idle learn procedure must be performed
- Turn ignition ON for 5 seconds. Turn ignition OFF for 5 seconds. Turn ignition ON for 5 seconds. Start engine in park/neutral.
- Allow engine to run until engine coolant is above 185° F (85° C). Turn A/C ON for 10 seconds, if equipped. Turn A/C OFF for 10 seconds, if equipped. If vehicle is equipped with an automatic transaxle, apply parking brake.
- While pressing brake pedal, place transaxle in D (drive). Turn A/C ON for 10 seconds, if equipped. Turn A/C OFF for 10 seconds, if equipped. Turn ignition OFF. The idle learn procedure is complete.
Note. Several symptom procedures call for a careful visual/physical inspection. Always perform visual/physical test first. Visual inspections may lead to correcting a problem without further checks and can save valuable time.
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Intermittents
The problem may or may not illuminate Malfunction Indicator Lamp (MIL) or store a diagnostic trouble code (DTC).
Note. Do not use DTC tables for intermittent problems. A fault must be present in order to locate problem. If a fault is intermittent, use of DTC tables may result in replacement of good parts.
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Hard Start
The engine cranks okay, but does not start for a long time. The engine eventually runs or may start and immediately die.
Note. Ensure that driver is using correct starting procedure. Before diagnosing, check service bulletins for updates.
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Surges Or Chuggles
Engine power varies under steady throttle or cruise, making it feel as if vehicle speeds up and slows down with no change in accelerator pedal position.
Note. Make sure driver understands Torque Converter Clutch (TCC) and A/C compressor operation as described in owner's manual. The speedometer reading and speed reading on scan tool should be equal. Before diagnosing symptom, check service bulletins for updates.
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Lack Of Power, Sluggishness, Or Sponginess
The engine delivers less than expected power. There is little or no increase in speed when accelerator pedal is partially applied.
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Hesitation, Sag, Or Stumble
Involves a momentary lack of response as accelerator is pushed down. This can occur at any vehicle speed. It is usually most severe when first trying to make vehicle move, as from a stop. Hesitation, sag, or stumble may cause engine to stall if severe enough.
Note. Before diagnosing this condition, check service bulletins for Programmable Read-Only Memory (PROM) updates.
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Cuts Out Or Misses
This involves a steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. The exhaust has a steady spitting sound at idle or low speed.
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Poor Fuel Economy
Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, fuel economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.
Note. Driving habits affect fuel economy. Check owner's driving habits by asking the following questions
- Is A/C system (i.e. defroster mode) turned on all the time?
- Are tires at correct air pressure?
- Have excessively heavy loads been carried?
- Does driver accelerate too much and too often? Suggest driver read section in owner's manual about fuel economy.
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Rough, Unstable, Or Incorrect Idle, Stalling
The engine runs unevenly at idle. If condition is bad enough, vehicle may shake. Also, idle varies in rpm (called "hunting"). Either condition may be severe enough to cause stalling. The engine idles at incorrect idle speed.
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Excessive Exhaust Emissions Or Odors
A vehicle fails an emission test. The vehicle has an excessive rotten egg smell.
Note. Excessive odors do not necessarily indicate excessive emissions.
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Dieseling Or Run-On
An engine continues to run after ignition switch is turned OFF.
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Backfire
Fuel ignites in intake manifold, or in exhaust system, making a loud popping noise.
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A/C Clutch
The A/C Relay represents a commanded state of A/C clutch control relay. The A/C clutch should be engaged when scan tool displays ON.
A/C Pressure
The A/C High Side displays pressure value of A/C refrigerant pressure sensor. The A/C High Side helps to diagnose Diagnostic Trouble Code (DTC) P0533.
A/C Request
The A/C Request represents whether air conditioning is being requested from HVAC selector. The input is received by instrument panel cluster and then sent over Universal Asynchronous Receiver Transmitter (WART) serial data to Powertrain Control Module (PCM)/Engine Control Module (ECM) and finally to scan tool over class 2 serial data.
Air Fuel Ratio
The Air Fuel Ratio indicates air to fuel ratio based on Oxygen Sensor (02S) inputs. The PCM/ECM uses fuel trims to adjust fueling in order to attempt to maintain an air fuel ratio of 14.7:1.
BARO
The Barometric Pressure (BARD) sensor measures change in intake manifold pressure which results from altitude changes. This value is updated at ignition ON and also at Wide Open Throttle (WOT).
BPW Bank 1
Indicates base Pulse Width Modulation (PWM) or ON time of indicated cylinder injector in milliseconds. When engine load is increased, injector pulse width will increase.
Calculated Air Flow
The calculated air flow is a calculation based on manifold absolute pressure. The calculation is used in several diagnostics to determine when to run diagnostics.
Calculated Load
Indicates engine load based on Manifold Absolute Pressure (MAP). The higher percentage, more load engine is under.
Camshaft Activity Counter
The Camshaft Position (CMP) activity counter displays activity sent to PCM/ECM from CMP sensor. The counter will continually increment while engine is running. The CMP activity counter is helpful in diagnosing DTC P0342.
Desired Idle
The PCM/ECM commands idle speed. The PCM/ECM compensates for various engine loads in order to maintain desired idle speed. The actual engine speed should remain close to desired idle under various engine loads with engine idling.
Engine Coolant Temperature
The Engine Coolant Temperature (ECT) sensor sends engine temperature information to PCM/ECM. The PCM/ECM supplies 5 volts to engine coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When sensor is cold (internal resistance high), PCM/ECM monitors a high voltage which it interprets as a cold engine. As sensor warms (internal resistance decreases), voltage signal will decrease and PCM/ECM will interpret lower voltage as a warm engine.
EGR Desired Position
The desired Exhaust Gas Recirculation (EGR) position is commanded EGR position. The PCM/ECM calculates desired EGR position. The higher percentage, longer PCM/ECM is commanding EGR valve ON.
Engine Run Time
The engine run time is a measure of how long engine has been running. When engine stops running, timer resets to zero.
Engine Speed
Engine Speed is computed by PCM/ECM from fuel control reference input It should remain close to desired idle under various engine loads with engine idling.
EVAP Purge
The Evaporative (EVAP) Emission purge valve solenoid is a proportional signal used in order to control EVAP canister purge function. At 0% valve is commanded fully closed. 100% implies that valve is fully open.
EVAP Purge Solenoid
When energized, EVAP Emission Canister Purge Solenoid allows fuel vapor to flow from EVAP Canister to engine. The EVAP Emission Canister Purge Solenoid is normally closed. The EVAP Emission Canister Purge Solenoid is pulse width modulated by PCM/ECM. The EVAP Emission Canister Purge Solenoid reads 0% when closed and 100% when fully opened.
EVAP Vent Solenoid
The EVAP Emission Vent Solenoid allows fresh outside air to EVAP Emission Canister during purge mode. The EVAP Emission Vent Solenoid allows diagnostic to pull a vacuum on fuel tank by closing vent solenoid.
Fan
The Fan Control (FC) Relay is commanded by PCM/ECM. The FC Relay displays command as ON or OFF.
Fuel Level Sensor
The Fuel Level Sensor monitors fuel level in tank. The Fuel Level Sensor monitors rate of change of air pressure in EVAP Emission Canister Purge System. Several of Enhanced EVAP Emission Canister Purge System diagnostics are dependent upon correct fuel level.
Fuel Tank Pressure Sensor
The fuel tank pressure sensor measures difference between pressure or vacuum in fuel tank and outside air pressure. When air pressure in fuel tank equals outside air pressure, output voltage of sensor is 1.3 to 1.7 volts.
IAC Position
The scan tool displays PCM/ECM command for Idle Air Control (IAC) pintle position in counts. The higher number of counts, greater commanded idle speed reads. The Idle Air Control responds to changes in engine load in order to maintain desired idle rpm.
Intake Air Temperature
The PCM/ECM converts resistance of Intake Air Temperature (IAT) sensor to degrees in same manner as ECT sensor. Intake air temperature is used by PCM/ECM to adjust fuel delivery and spark timing according to incoming air density.
Ignition 1 (Voltage)
The ignition volts represent system voltage measured by PCM/ECM at ignition feed circuit.
Knock Retard
The Knock Sensor (KS) Retard indicates amount of spark advance PCM/ECM is decreasing in response to KS signal.
Knock Present
The KS Noise Channel indicates when PCM/ECM detects KS signal. The PCM/ECM should display NO at idle.
Long Term FT
The Long Term Fuel Trim (FT) is derived from short term fuel trim value. The Long Term FT is used for long term correction of fuel delivery. A value of 128 counts (0%), indicates that fuel delivery requires no compensation in order to maintain a 14.7:1 air to fuel ratio. A value below 128 counts means that fuel system is too rich and fuel delivery is being reduced. The PCM/ECM is decreasing injector pulse width. A value above 123 counts indicates that a lean condition exists for which PCM/ECM is compensating.
Long Term FT Average
Long Term FT Average is derived from long term fuel trim from all of cells. The PCM/ECM then takes all of values and then creates one average value.
Loop Status
The Closed Loop is displayed indicating that PCM/ECM is controlling fuel delivery according to Oxygen Sensor (02S) voltage as close to an air/fuel ratio of 14.7 to 1 as possible.
MAP
The MAP sensor measures change in intake manifold pressure which results from engine load and speed changes. As intake manifold pressure increases, air density in intake also increases and additional fuel is required.
Misfire Current #1-4
Indicates number of current misfires that are present in indicated cylinder. Increments only when misfire is current.
Misfire History #1-4
Indicates number of misfires that have occurred after 195 current misfires have been counted. The current misfire counter will add its misfires to history misfire counter after 195 total misfires have taken place. If 1 cylinder is misfiring, misfiring current counter will have 195 misfires counted before adding to its history counter. If 2 cylinders are misfiring, misfiring current counter will add to history counters after 97 misfires. The counter increments only after a misfire Diagnostic Trouble Code (DTC) has been set.
Oxygen Sensor Bank 1 Sensor 1
The pre Oxygen Sensor (02S) reading represents exhaust oxygen sensor output voltage. This voltage will fluctuate constantly between 100 mv (lean exhaust) and 900 mv (rich exhaust) when system is operating in a Closed Loop.
Oxygen Sensor Bank 1 Sensor 2
The post Heated Oxygen Sensor (HO2S) represents exhaust oxygen output voltage past catalytic converter. This voltage remains inactive, or voltage will appear lazy within a range of 100 mv (lean exhaust) and 900 mv (rich exhaust) when operating in a Closed Loop.
Short Term FT
The Short Term FT represents a short term correction to fuel delivery by PCM/ECM in response to amount of time oxygen sensor voltage spends above or below 450 mv threshold. If oxygen sensor has mainly been below 450 mv, indicating a lean air/fuel mixture, short term fuel trim will increase to tell PCM/ECM to add fuel. If oxygen sensor voltage stays mainly above threshold, PCM/ECM will reduce fuel delivery to compensate for indicated rich condition.
Short Term FT Average
The Short Term FT Average is derived from short term fuel trim from all of cells. The PCM/ECM takes all of values and then creates one average value.
Spark
This is a display of spark advance Ignition Coil (IC) calculation which PCM/ECM is programming in ignition system. It computes desired spark advance using data such as engine temperature, rpm, engine load, vehicle speed and operating mode.
TCC Brake Switch
When brake pedal is applied, Torque Converter Clutch (TCC) brake switch sends a signal to PCM/ECM to disengage TCC and disable cruise control.
Total Misfire Current Counter
Indicates total number of misfires that have been detected in all cylinders after 100 engine cycles. One cycle equals one complete 4 stroke cycle. The total misfire only increments during steady state cruise conditions.
TP Angle
From Throttle Position (TP) Sensor voltage input, PCM/ECM computes TP. The TP Angle will auto zero to 0% at idle (TP voltage below .90 volts). The TP Angle will read 100% at WOT
TP Sensor
The PCM/ECM uses TP Sensor in order to determine amount of throttle demanded by vehicle is operator The TP Sensor reads between .36-.96 volts at idle to above 4 volts at WOT.
Vehicle Speed
The vehicle speed sensor signal is converted into mph or km/h for display The vehicle speed output from PCM/ECM is 4000 pulses per mile. The scan tool uses class 2 serial data from PCM/ECM to obtain vehicle speed, while Instrument Panel Cluster (IPC), cruise control module and chime alarm module use 4000 ppm output.
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Gasoline
All engines are designed to use unleaded fuel only. Unleaded fuel must be used for proper emission control system operation. Its use will also minimize spark plug fouling and extend engine oil life. Using leaded fuel can damage emission warranty coverage. The fuel should meet specification ASTM D4814 for U.S. or CGSB 3.5 M93 for Canada. All engines are designed to use unleaded fuel with a minimum U(R+M)/2e (pump) octane number of 87. where R=research octane number, and M=motor octane number.
Ethanol
You may use fuel containing ethanol (ethyl alcohol) or grain alcohol providing that there is not more than 10 percent ethyl alcohol by volume.
Methanol
Do not use fuels containing methanol. Methanol can corrode metal parts and also cause damage to plastic and rubber parts in fuel system.
Methyl Tertiary-Butyl Ether (MTBE)
You may use fuel containing Methyl Tertiary-Butyl Ether (MTBE) providing there is not more than 15 percent MTBE by volume.
