Acura NSX 1997 Service Manual page 208

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Troubleshooting
Troubleshooting Procedures (cont'd)
ECM Data
By connecting the OBD II scan tool or the Honda PGM Tester to the 16P data link connector (DLC), various data can be
retrieved from the ECM. The items listed in the table below conform to the SAE recommended practice.
The Honda PGM Tester also reads data beyond that recommended by SAE.
Understanding this data will help to find the causes of intermittent failures or engine problems.
NOTE:
The "operating values" given below are approximate values and may be different depending on the environment and
the individual vehicle.
Unless noted otherwise, "at idle speed" means idling with the engine completely warmed up, A/T in
M/T in neutral, and the A/C and all accessories turned off.
Data
Diagnostic If the ECM detects a problem, it will store it as a code
Trouble Code consisting of one letter and four numbers.
Depending on the problem, an SAE-defined code
(DTC)
(POxxx) or a Honda-defined code (P1xxx) will be output
to the tester.
Engine Speed The ECM computes engine speed from the signals sent
from the Crankshaft Position sensor.
This data is used for determining the time and amount
of fuel injection.
Vehicle Speed The ECM converts pulse signals from the Vehicle
Speed Sensor (VSS) into speed data.
Manifold The absolute pressure created in the intake manifold by
Absolute engine load and speed.
Pressure (MAP)
Engine Coolant The ECT sensor converts coolant temperature into volt-
Temperature age and signals the ECM. The sensor is a thermistor
(ECT) whose internal resistance changes with coolant tem-
perature. The ECM uses the voltage signals from the
ECT sensor to determine the amount of injected fuel.
Heated Oxygen The Heated Oxygen Sensor detects the oxygen content
Sensor (HO2S) in the exhaust gas and sends voltage signals to the
(Bank 1, Sensor 1) ECM. Based on these signals, the ECM controls the
(Bank 1, Sensor 2) air/fuel ratio. When the oxygen content is high (that is,
(Bank 2, Sensor 1) when the ratio is leaner than the stoichiometric ratio),
(Bank 2, Sensor 2) the voltage signal is lower. When the oxygen content is
low (that is, when the ratio is richer than the stoichio-
metric ratio), the voltage signal is higher.
Table of Contents
Description Operating Value
If no problem is detected,
there is no output.
Nearly the same as
tachometer indication at
idle speed:
A/T: 780 ± 50 rpm
M/T: 800 ± 50 rpm
Nearly the same as
speedometer indication
With engine stopped:
Nearly the same as atmo-
spheric pressure at idle
speed:
24-37kPa(180-280
mmHg, 7.1-11.0 inHg)
With cold engine:
Same as ambient temper-
ature and IAT
With engine warmed up:
approx. 176-194°F
(80 - 90°C)
0.0-1.25V
At idle speed:
about 0.1-0.9V
or position,
Freeze Data
YES
YES
YES
YES
YES
NO