Honda CR-V 1997 Service Manual page 268

Troubleshooting
Troubleshooting Procedures (cont'd)
Data Description Operating Value Freeze Data
H02S loop
slatus
is indicated as "open" or "closed" .
At idle speed: closed
Feedba ck Closed: Based on the H02S output, the ECM/PCM deter-
Loop Status mines the air/fuel ratio and controls the amount of
injected fuel.
YES
Open: ignoring H02S output, the ECM/PCM refers to sig-
nals from the TP, MAP. and EeT sensors to control the
amount of injected fuel.
Short Term The air/fuel ratio correction coefficient for correcting the
± 20%
Fuel Trim amount of injected fuel when H02S feedback is in the
closed loop status. When the signal from the H02S is
weak, short term fuel trim gets higher, and the ECMtpCM
increases the amount of injected fuel. The air/fuel ratio
YES
gradually gets richer, causing a higher H02S output.
Consequently, the short term fuel trim is lowered, and
the ECM/PCM reduces the amount of injected fuel.
This cycle keeps the air/fuel ratio close to the
stoichio ~
metric ratio when in closed loop status.
r---
Long Term
Long term fuel trim is computed from short term fuel ± 20%
Fuel Trim trim and indicates changes occuring in the fuel supply
system over a long period .
YES
If long term fuel trim is higher than' .00, the amount of
injected fuel must be increased. If it is lower than 1.00,
the amount of injected fuel must be reduced .
Intake Air The IAT sensor converts intake air temperature into
volt~ With cold engine:
Temperature
age and signals the ECM/PCM. When intake air tempera-
Same as ambient
temper~
YES
(lAT)
ture is low, the internal resistance of the sensor
ature and ECT
increases, and the voltage signal is higher.
Throttle
Based on the accelerator pedal position, the opening
At idle speed:
YES
Position angle of the throttle valve is indicated. approx. 10%
Ignition Ignition timing is the ignition advance angle set by the
At idle speed: 16' ± 4'
Timing ECM/PCM. The ECM/PCM matches ignition timing to the
BTDC with the SCS ser-
NO
driving conditions. vice connector connected.
Calculated ClV is the engine load calculated from the MAP data.
At idle speed:
load Value 28 - 41%
YES
(ClVI At 2,500 rpm with no load:
13 - 26%
11-66