Scan Tool Data Definitions
A list of explanations for each data message displayed on the scan tool
begins below. This information will assist you in tracking down emission or
driveability problems since the displays can be viewed while the vehicle
is being driven. Refer to the for additional information.
Engine Speed: The scan tool range is 0-3175 RPM. Engine speed is
computed by the ECM from the ignition reference pulses. It should remain
close to desired idle under various engine loads with engine idling.
Desired Idle Speed: The scan tool range is 0-3175 RPM. The desired idle
is the idle speed that is commanded by the ECM. The ECM will compensate for
various engine loads based to keep the engine at the desired idle speed.
ECT: The scan tool range is 40°C-199°C (-40°F-389°F).
The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold
and sends engine temperature information to the ECM.The ECM supplies 5 volts
to the ECT sensor circuit. The sensor is a thermistor which changes internal
resistance as temperature changes. When the sensor is cold (internal resistance
high), the ECM monitors a high signal voltage and interprets it as a cold
engine. As the sensor warms (internal resistance decreases), the voltage
signal will decrease and the ECM will interpret the lower voltage as a
warm engine.
MAP Sensor: The scan tool range is 10-205 kPa, 0.00-5.10 volts.
The manifold absolute pressure (MAP) sensor measures the change in the intake
manifold pressure from engine load and speed changes. As intake manifold
pressure increases, intake vacuum decreases resulting in a higher MAP sensor
voltage and kPa reading. The MAP sensor signal is used for the following:
(1) To update the BARO reading; (2) Enabling factor for several of the
diagnostics.
Throttle Position: The Throttle Position (TP) sensor produces a voltage proportional
to the position of the throttle valve. It is used to indicate to the ECM how
much throttle is being commanded by the driver. A reading close to 5.10 volts
means full throttle, while a reading of 0.00 volts corresponds to
idle throttle.
Throttle Angle: Computed by the ECM from the TP sensor voltage, throttle position
should read 0% at idle and 100% at wide open throttle.
O2S: The scan tool range is 0-1800 mV. The scan tool display
represents the exhaust Oxygen sensor (02S) output voltage. The voltage should
fluctuate constantly within a range between 100 mV (lean exhaust),
and 1000 mV (rich exhaust), while operating in closed loop.
Loop Status: This position will indicate whether the control module is operating
in Open or Closed Loop. Most systems go Closed Loop after a certain amount
of run time, when engine coolant temperature is high enough, and the oxygen
sensors becomes active.
Rich/Lean Status: Scan tool displays Rich or Lean. Indicates whether the exhaust
oxygen sensor voltage is above (rich) or below (lean) the 450 mV oxygen
threshold voltage. The display should change constantly indicating that
the ECM is controlling the air/fuel mixture properly.
O2S Cross Counts: The scan tool range is 0-255. This is the number of times
the O2S voltage crosses over the rich/lean threshold during a one second interval.
KS Activity: The scan tool displays Yes or No. The display indicates whether
or not a KS activity is being detected by the ECM. With the engine idling,
the scan tool should indicate No at idle..
Long Term FT Bank : The scan tool range is 0-255. Block learn is derived from
the fuel intergrator value and is used for long-term correction of
fuel delivery. A value of 128 counts indicates that the fuel delivery requires
no compensation to maintain a 14.7:1 air/fuel ratio. A value below 128 counts
means that the fuel system is too rich and fuel delivery is being reduced
(decreased injector pulse width). A value above 128 counts indicates that
a lean condition exists and the ECM is compensating by adding fuel (increased
injector pulse width).
Long Term FT Bank : The scan tool displays percentage. Long term fuel trim is derived
from the short term fuel trim value and represents a long term correction
of fuel delivery. A value of 0%/128 indicates that fuel delivery requires
no compensation to maintain the ECM commanded air/fuel ratio. A negative value
significantly below 0%/128 indicates that the fuel system is rich and fuel
delivery is being reduced (decreased injector pulse width). A positive value
significantly greater than 0%/128 indicates that a lean condition exists and
the ECM is compensating by adding fuel (increased injector pulse width).
Short Term FT Bank : The scan tool range is 0-255.Fuel intergrator represents
a short term correction to fuel delivery by the ECM in response to the amount
of time the fuel control oxygen sensor voltage spends above or below the
450 mV threshold. If the oxygen sensor voltage has mainly remained
less then 450 mV, indicating a lean air/fuel mixture. Fuel intergrator
will increase and the ECM will add fuel. If the oxygen sensor voltage stays
mainly above the threshold, the ECM reduces fuel delivery to compensate
for the indicated rich condition.
Short Term FT Bank: The scan tool displays percentage. Short term fuel trim represents
a short term correction to fuel delivery by the ECM in response to the amount
of time the fuel control oxygen sensor voltage spends above or below the 450mV
threshold. If the oxygen sensor voltage has mainly remained less than 450mV,
indicating a lean air/fuel mixture,short term fuel trim will increase into
the positive range above 0%/128 and the ECM will add fuel. If the oxygen sensor
voltage stays mainly above the threshold, short term fuel trim will decrease
below 0%/128 into the negative range while the ECM reduces fuel delivery to
compensate for the indicated rich condition.Under certain conditions such
as extended idle and high ambient temperatures, canister purge may cause short
term fuel trim to read in the negative range during normal operation. Fuel
trim values at maximum authority may indicate an excessively rich or lean
system.
Idle Air Control: The scan tool range is 0-255. The scan tool displays the
commanded position of the idle air control pintle in counts. The higher the
number of counts, the greater the commanded idle speed. Idle air control
should respond fairly quickly to changes in engine load to maintain desired
idle RPM.
PNP: The scan tool displays R-D321, or neutral. Medium duty trucks
do not have a park gear. When the transmission is in neutral, the scan tool
will read
NEUTRAL
. When it is in gear it will
read
R-D321.
System Voltage Ignition 1: The scan tool range is 0-25.5 volts. This represents
the system voltage measured by the ECM at its ignition feed.
Fuel Pump Volts: The scan tool range is 0-25.5 volts. This represents
the voltage found at the fuel pump. It is used by the ECM as the system voltage.
The ECM uses fuel pump volts as a reference to determine electrical loading.
A/C Clutch: The air conditioner clutch is a feedback signal to the ECM that
lets the ECM know if the A/C clutch is ON or OFF.
Gov. Overspeed Lamp.: The scan tool reads OFF or ON. For medium duty trucks there is
an engine overspeed governor that keeps the engine from over revving. When
the ECM recognizes that the engine is spinning too fast, it turns ON a dash
light and this parameter will read ON.
Vehicle Speed: The scan tool displays 0-255 km/h (0-158 mph).
The vehicle speed sensor signal is converted into km/h and mph for display.
PROM ID: This parameter describes the particular PROM used in the ECM being
tested. The PROM contains the ECM program. Calibration ID is used when its
necessary to replace the PROM. Calibration ID must be specified when ordering
new PROM(s). Calibration ID should not be confused with the part number.