PCM Data Description
The following information will assist in diagnosing emission or driveability
problems. The technician can view the displays while driving the vehicle.
Refer to Powertrain OBD System Check for additional information.
The displayed data messages on the scan tool are divided into the Engine,
the Specific Engine and the DTC lists as follows:
Engine Data
• | Engine 1 -- Contains general information regarding the fuel
delivery, the Ignition Control (IC), the Knock Sensor (KS), the Evaporative
Emission (EVAP) and the basic engine operating conditions. |
• | Engine 2 -- Contains general information regarding the fuel
delivery Output Controls, the Ignition Control (IC), the Air Conditioning
(A/C), the cruise control, and the basic engine operating conditions. |
Specific Engine Data
• | Misfire -- Contains the information that is specific to the
diagnosis of the misfire and the data that is required in order to verify
the proper operation with regard to the misfire. |
• | O2S -- Contains the information that is specific to the
Oxygen Sensor (O2S 1) and the Rear Heated Oxygen Sensor (HO2S 2)
diagnosis and the data that is required in order to verify the proper
operation of the sensors. |
DTC Data
• | Freeze Frame -- Contains the information that was collected
during the time that a MIL requesting DTC was set. This allows the technician
to re-create the conditions when a fault occurred and to verify the
proper operation within these conditions. |
• | Failure Records -- Contains the information at the time
a diagnostic test failed and set a DTC. The failure records data is not necessarily
associated with the MIL. |
Engine Scan Tool Data Definitions
A/C High Side Pressure--Range 0-5.0 Volts: The A/C High Side displays the pressure value of the A/C refrigerant
pressure sensor. The A/C High Side helps diagnose DTC P0530.
A/C High Side Pressure--Range 0-459 PSI: The A/C High Side displays the pressure value of the A/C refrigerant
pressure sensor. The A/C High Side helps diagnose DTC P0530.
Another TWC Test Desired--Range Yes/No: The display shows Yes or No. The display indicates if another catalyst
test is needed for a catalyst test decision. The PCM may need another test
to determine if the catalyst is operating properly.
A/C Relay --Range OFF/ON: The A/C Relay represents the commanded state of the A/C clutch
control relay. The A/C clutch should be engaged when the scan tool displays
on.
A/C Request-- Range Yes/No: A/C Request--This displays if PCM has received an A/C request
from body control module (BCM).
Adaptive Knock Retard--Range 0-90 degrees: The Adaptive Knock Retard indicates the long term amount of the
spark advance the PCM removes from the ignition control (IC). The PCM responds
to the knock sensor (KS) signal.
Air Fuel Ratio--Range 0:1-25.5:1: The Air Fuel Ratio indicates the air to fuel ratio based on the
oxygen sensor (O2S 1) inputs. The PCM uses the fuel trims to adjust
fueling in order to maintain an air fuel ratio of 14.7:1.
BARO--Range 11-105 kPa, 0-5.0 Volts: The barometric pressure (BARO) sensor measures the change in the
intake manifold pressure which results from altitude changes. This value is
updated at ignition on and also at wide open throttle (WOT).
Base PWM Cyl. 1-4 - Range 0-999.9 mS: Indicates the base pulse width modulation (PWM) or on-time of the
indicated fuel injector in milliseconds. When the engine load is increased,
the injector pulse width will increase.
Calc. Air Flow--Range 0-512 grams/second: The calculated air flow is a calculation based on manifold absolute
pressure. The calculation is used in several diagnostics to determine when
to run.
Calc. Vacuum--Range 0-80 kPa: The display shows the calculated vacuum which is an indication
of engine load. The calculated vacuum is the difference between the BARO reading
and the MAP sensor reading. The lower the Calc. Vacuum value, the higher
the engine load.
Calc. Convertor Temp.--Range 300-1000°C (572-1832°F): Display shows temperature in degrees C and degrees F from 0°C
(32°F) to 765°C (1409°F). This parameter is the PCM calculated
temperature of the 3-way catalyst.
CKP Active Counter (7X Reference)-- Range 0-255 Counts: The crankshaft position (CKP) activity counter displays whether
the PCM is receiving the 7X sync pulses from the ignition module. Helpful
in diagnosing DTC P0335 and Cranks But Will Not Run conditions.
CMP Active Counter--Range 0-255 Counts: The camshaft position (CMP) activity counter displays the activity
sent to the PCM from the CMP sensor. The counter will continually increment
while the engine is running. The CMP Act. Counter is helpful in
diagnosing the DTC P0342.
CMP Resync Counter--Range 0-255 Counts: The camshaft position (CMP) resync counter displays the number
of times the PCM had to resync with the CMP sensor. The CMP Resync Counter
is helpful in diagnosing the DTC P0341.
Cruise--Range Disable/Enabled: The stepper cruise display indicates if the PCM is allowing the
cruise operation. The PCM has the ability to disable the cruise control under
certain conditions.
Cruise--Range Engaged/Disengaged: Cruise engaged is an input from the cruise control module to the
PCM and indicates if the cruise control system is in control of vehicle speed.
The PCM uses this information to change transmission shift calibrations
and to turn on an indicator lamp on the instrument panel cluster
(IPC), if equipped.
Current TWC Test Complete--Range Yes/No: The display shows Yes or No. This display indicates that at least
one pass or fail test decision has been made during the idle catalyst test
(P0420). It takes only one test to obtain a pass decision, but six
tests may be required to obtain a fail decision.
Desired Idle Speed-- 0-3187 RPM: The PCM commands the idle speed. The PCM compensates for various
engine loads in order to maintain the desired idle speed. The actual engine
RPM speed should remain close to the desired idle under the various
engine loads with the engine idling.
ECT--Range -40°C-151°C (-40°F-304°F): The engine coolant temperature (ECT) sensor sends engine temperature
information to the PCM. The PCM supplies 5 volts to the engine coolant
temperature sensor circuit. The sensor is a thermistor which changes
internal resistance as temperature changes. When the sensor is
cold (internal resistance high), the PCM monitors a high voltage
which it interprets as a cold engine. As the sensor warms (internal
resistance decreases), the voltage signal will decrease and the
PCM will interpret the lower voltage as a warm engine.
ECL--Range Low/OK: The engine coolant level is displayed as Low or OK. This indicates
whether the coolant in the radiator surge tank is Low or OK.
Engine LOAD--Range 0-100%: Indicates the engine load based on manifold absolute pressure.
The higher the percentage, the more load the engine is under.
Engine Oil Pressure--Range Low/OK: The engine oil pressure switch sends an input to the PCM to indicate
whether the engine oil pressure is Low or OK.
Engine Run Time--Range 0:00:00-18:12:15 hours:minutes:seconds: The engine run time is a measure of how long the engine has been
running. When the engine stops running, the timer resets to zero.
Engine Speed--Range 0-6384 RPM: Engine Speed is computed by the PCM from the fuel control reference
input. It should remain close to desired idle under the various engine loads
with the engine idling.
EVAP Canister Purge--Range 0-100%: The evaporative emission (EVAP) purge valve solenoid is a proportional
signal used in order to control the evaporative emission canister purge function.
At 0 percent the valve is commanded fully closed. 100 percent implies
that the valve is fully open.
EVAP Vent Solenoid -- Range OFF/ON: The EVAP vent solenoid allows fresh outside air to the EVAP canister
during the purge mode. The EVAP vent Solenoid allows the diagnostic to pull
a vacuum on the fuel tank by closing the vent solenoid.
Fan Control Relay 1--Range OFF/ON: The fan control (FC) relay is commanded by the PCM. FC relay 1
displays the command as on or off.
Fan Control Relay 2--Range OFF/ON: The fan control (FC) relay is commanded by the PCM. FC relay 2
displays the command as on or off.
Fuel Pump Relay Command--Range Off/On: The Fuel Pump Relay is commanded by the PCM. When the ignition
is on the PCM supplies voltage to the Fuel pump relay which supplies voltage
to the Fuel pump and Fuel Injectors.
Fuel Tank Pressure -- Range -25.89 - 32.45 mm hg: The fuel tank pressure sensor measures the difference between the
pressure or the vacuum in the fuel tank and the outside air pressure. When
the air pressure in the fuel tank equals the outside air pressure,
the output voltage of the sensor is 1.3 to 1.7 volts.
Fuel Tank Pressure -- Range - 0.0-5.0 Volts: The fuel tank pressure sensor measures the difference between the
pressure or the vacuum in the fuel tank and the outside air pressure. When
the air pressure in the fuel tank equals the outside air pressure,
the output voltage of the sensor is 1.3 to 1.7 volts.
Fuel Level Sensor Range -- 0 Percent- -100 Percent: The fuel level sensor monitors the fuel level in the tank. Several
of the Enhanced EVAP system diagnostics are dependent upon the correct
fuel level reading.
Fuel Trim Cell--Range 0-22: A Fuel Trim Cell depends upon the engine speed and the MAP sensor
readings. RPM vs. MAP is broken down into 22 fuel trim cells. The Fuel Trim
Cell indicates which cell is currently active.
FT Index--Range 0-255 (-100% to 100%): Fuel Trim (FT) Index represents the average Long Term Fuel Trim
for certain cells which are used in determining DTC P0171 and P0172.
GEN L Terminal--Range Inactive/Active: The generator L terminal indicates whether the PCM is allowing
the generator to operate. The PCM can disable the generator under certain
conditions to ease starting. Inactive indicates that the PCM is
allowing generator operation, while active indicates that the PCM
is not allowing generator operation.
GEN PWM Range 0-100%: The generator F terminal is the duty cycle or load input to the
PCM from the generator. As the generator load increases, the PCM will adjust
idle speed accordingly.
HO2S 2 - Range 0-1132 mV: The rear heated oxygen sensor (HO2S 2) represents the exhaust
oxygen output voltage past the catalytic converter. This voltage remains inactive,
or the voltage will appear lazy within a range of 100 mV
(lean exhaust) and 900 mV (rich exhaust) when the system
is operating in a Closed Loop.
IAC Position--Range 0-255 Counts: The idle air control (IAC) pintle position command from the PCM
is displayed in counts. The higher the counts read, the greater the commanded
idle speed is. The idle air control responds fairly quickly to
changes in the engine load in order to maintain the desired idle
RPM.
IAT--Range -40°C-151°C (-40°F-304°F): The PCM converts the resistance of the intake air temperature (IAT)
sensor to degrees in the same manner as the ECT sensor. Intake air temp is
used by the PCM to adjust fuel delivery and spark timing according
to incoming air density.
Ignition 1--Range 0-25.5 volts: The ignition volts represents the system voltage measured by the
PCM at the ignition feed circuit.
KS Noise Channel--Range 0-5 volts: The KS Noise Channel indicates when the PCM detects the knock sensor
(KS) signal. The PCM should display close to 1.0 volt at idle.
KS Retard--0-90 degrees: The KS retard indicates the amount of spark advance the PCM is
removing in response to the KS signal.
Lean/Rich Transition -- Range 0-255 counts: The PCM counts the number of times the oxygen sensor (O2S 1)
goes from a low voltage (lean exhaust) to a high voltage (rich exhaust) within
a 100 second period. Lean/Rich Transition should increment
when the vehicle is operating within the Conditions for Setting
in DTC P0133 or DTC P1133.
Lean/Rich Avg. -- Range 0-249 mS counts: The PCM takes the Lean/Rich transition times following the completion
of the data collection period as specified in the Conditions for Setting in
DTC P0133 and DTC P1133. Then the PCM averages the transition time
from the total transition times.
Long Term FT--Range 0-255 (-100% to 100%): The Long Term Fuel Trim (FT) is derived from the short term fuel
trim value. The Long Term Fuel Trim (FT) is used for the long term correction
of the fuel delivery. A value of the 128 counts (0 percent)
indicates that the fuel delivery requires no compensation in order
to maintain a 14.7:1 air-to-fuel ratio. A value below 128 counts
means that the fuel system is too rich and the fuel delivery is
being reduced. The PCM is decreasing the injector pulse width.
A value above 128 counts indicates that a lean condition
exists for which the PCM is compensating.
Loop Status--Range Open/Closed: A Closed Loop displayed indicates that the PCM is controlling the
fuel delivery according to the oxygen sensor (O2S 1) voltage. The PCM
controls the fuel delivery air-to-fuel ratio as close to 14.7:1
as possible.
MAP - Range 11-105 kPa, 0-5.0 Volts: The manifold absolute pressure (MAP) sensor measures the change
in the intake manifold pressure which results from engine load and speed changes.
As the intake manifold pressure increases, the air density in the
intake also increases and additional fuel is required.
MIL -Scan Tool displays OK, Faulty, or Invalid state: These parameters describe the condition of the Control Circuit.
Misfire Current #1-4 -- Range 0-255 Counts: Indicates the number of current misfires that are present in the
indicated cylinder. Increments only when misfire is current.
Misfire History #1-4 -- Range 0-255 Counts: Indicates the number of misfires that have occurred after 195 current
misfires have been counted. The current misfire counter will add misfires
to the history misfire counter after 195 total misfires have taken
place. If 1 cylinder is misfiring, the misfiring current counter
will have 195 misfires counted before adding to the history counter.
If 2 cylinders are misfiring, the misfiring current counters will
add to the history counters after 97 misfires. Increments only
after a misfire DTC has been set.
Med. Resolution Resync Counter--Range 0-255 Counts: The medium resolution resync counter displays the number of times
the PCM had to resync the crankshaft position (CKP) sensor. The Med. Resolution
Resync Counter is helpful in diagnosing the DTC P0335.
Med. Resolution Engine Sync.--Range YES/NO: The medium resolution engine sync. displays if the PCM is receiving
the 7x sync pulse. The Med. Resolution Engine Sync. is helpful in diagnosing
the DTC P0300 and P0301-P0304.
Number of DTCs--Range 0-255: The number of Current DTCs indicates the total number of current
DTCs set. The current DTCs set does not necessarily mean that the
MIL is illuminated.
Number of Catalyst Mon Test Completed--Range 0 - 255: The Catalyst Mon. Test completed sample counter is the total number
of test samples this ignition cycles. The Samples counter should never indicate
more than 1 unless the technician has cleared a DTC or disconnected
the battery.
O2S 1 - Range 0-1132 mV: The oxygen sensor (O2S 1) reading represents the exhaust oxygen
sensor output voltage. This voltage will fluctuate constantly between 100 mV
(lean exhaust) to 900 mV (rich exhaust) when operating in
a Closed Loop.
Output Driver 1 - Range SHRT00000000 Open00000000 (binary display): Output driver modules are used to allow various systems to function
by providing a ground circuit. The scan tool will display 0s in each of the
8 positions when the circuitry is OK. If a 1 appears in any of
the positions, either a short or an open circuit is being detected.
Output Driver 2 - Range SHRT00000000 Open00000000 (binary display): Output driver modules are used to allow various systems to function
by providing a ground circuit. The scan tool will display 0s in each of the
8 positions when the circuitry is OK. If a 1 appears in
any of the positions, either a short or an open circuit is being detected.
Park/Neutral Position Switch--Range Park/Reverse/Neutral/Overdrive/Drive
3/Drive 2/Low/Invalid: The scan tool displays the decoded position of the park/neutral
position switch PRNDL inputs. This information is then sent by Class 2 serial
data to the IPC. If a valid combination of inputs is not seen by
the PCM, Invalid will be displayed.
Park/Neutral Position Switch P, A, B, C--Range High or Low: A transaxle mounted switch is used as an input to let the PCM know
what position the gear select lever is in. The scan tool status will switch
from High to Low as different combinations are met. In Park, PRNDL
P and A will be Low and B and C will be High.
Power Enrichment--Range Active/Inactive: The scan tool indicates when power enrichment mode is active. This
is helpful in diagnosing DTC P1171.
Purge Learn Memory--Range 0.00-1.00: The purge learn memory is a display of the PCM adding or subtracting
the fuel. The purge learn memory is based on the EVAP purge. This number is
added to the fuel trim calculations. The fuel is added or subtracted
there. A number near 1 indicates that the fuel is being
added to the fuel trim. A number near 0 indicates that fuel
is being taken away from the fuel trim.
Rich/Lean Transition -- Range 0-255 counts: The PCM counts the number of times the O2S 1 switches from
a high voltage (rich exhaust) to a low voltage (lean exhaust) within
a 100 second period. Rich/Lean Transition should increment when
the vehicle is operating within the Conditions for Setting in
DTC P0133 or DTC P1133.
Rich/Lean Avg. -- Range 0-249 mS: The PCM takes the Rich/Lean transition value following the completion
of the data collection period as specified in the Conditions for Setting
in DTC P0133 and DTC P1133. Then the PCM divides
the value with the 100 second period.
Rich/Lean to Lean/Rich Ratio Sen. 1 -- Range 0:1-15.93:1: The Rich/Lean average is divided by the Lean/Rich average in order
to find the O2S 1 ratio.
Short Term FT--Range 0-255 (-100% to 100%): Short Term Fuel Trim (FT) represents a short term correction to
fuel delivery by the PCM in response to the amount of time the oxygen sensor
voltage spends above or below the 450 mV threshold. If the
oxygen sensor has mainly been below 450 mV, indicating a
lean air/fuel mixture, the short term fuel trim will increase to
tell the PCM to add fuel. If the oxygen sensor voltage stays mainly
above the threshold, the PCM will reduce fuel delivery to compensate
for the indicated rich condition.
Spark--Range 64 to -64 degrees: This is a display of the spark advance calculation which the PCM
is programming in the ignition system. It computes the desired spark advance
using data such as engine temperature, RPM, engine load, vehicle
speed, and operating mode.
TCC Brake Switch--Range Open/Closed: When the brake pedal is applied, the torque converter clutch (TCC)
brake switch sends a signal to the PCM to disengage the TCC and disable cruise
control.
Total Misfire Current Counter-- Range 0-255 Counts: The Total Misfire indicates the total number of misfires that have
been detected in all cylinders after 100 engine cycles. One cycle equals the
completion of a 4 stroke cycle. The total misfire only increments
during a steady state cruise conditions.
TP Angle--Range 0-100%: The PCM computes the throttle position (TP) from the TP sensor
voltage input. The TP angle will auto zero to 0% at idle when the TP voltage
is below 0.90 volt. The TP angle will read 100% at WOT.
(WOT).
TP Sensor--Range 0.0-5.0 Volts: The PCM uses the TP sensor to determine the amount of the throttle
demanded by the operator of the vehicle. The TP sensor reads between
0.36-0.96 volt at idle to above 4.0 volts at
WOT.
Transmission Range Switch P/A/B/C--Scan Tool displays High or Low: The Trans Switch P/A/B/C display represents the state of the four
inputs from the trans axle range switch. High display indicates battery voltage
signal being monitored at the PCM. Low indicates a ground input signal
at the PCM. The combination of transaxle range inputs indicates the position
of the transaxle manual valve.
TWC Stage 1 Started--Range Yes/No: The display shows Yes or No. This display indicates that the first
air/fuel transition of the Idle Catalyst test (P0420) is in progess.
TWC Stage 2 Started--Range Yes/No: The display shows Yes or No. This display indicates that the first
air/fuel transition of the Idle Catalyst test is in progess.
TWC System Related DTC is Set--Range Yes/No: The display shows Yes or No. This display indicates if a DTC is
set that will prevent the Idle Catalyst test from running.
TWC Test Initialization Conditions Met--Range Yes/No: Display shows Yes or No. This display says that the idle conditions
required to test the catalyst are met.
TWC Test Enabled--Range Yes/No: The display shows Yes or No. This display indicates the Idle
Catalyst test has started to run. There is a 5 second delay between
the TWC Test Initialization Conditions Met and the Idle Catalyst test
being enabled.
TWC Warmup Conditions Met--Range Yes/No: Display shows Yes or No. This display says that the warm-up conditions
required to test the catalyst are met and the catalyst is sufficiently warmed
up.
Vehicle Speed--Range 0-255 MPH, 0-255 km/h: The vehicle speed sensor signal is converted into km/h (MPH) for
display. The vehicle speed output from the PCM is 4000 pulses per mile.
The scan tool uses the Class 2 serial data from the PCM to obtain
vehicle speed, while the instrument panel cluster, the cruise control
module, and the multi-function alarm module use the 4000 ppm
output.