Daewoo MATIZ Service Manual page 204

1F – 106 ENGINE CONTROLS
DIAGNOSTIC TROUBLE CODE (DTC) – P0171 FUEL TRIM SYSTEM TOO LEAN
System Description
To provide the best possible combination of driveability,
fuel economy, and emission control, a Closed Loop air/
fuel metering system is used. While in Closed Loop, the
Engine Control Module (ECM) monitors the oxygen sen-
sor (O2S) signal voltage and adjusts fuel delivery based
on signal voltage. A change made to fuel delivery will be
indicated by the long and short term fuel trim values
which can be monitored with the scan tool. Ideal fuel trim
values are around 128 (0%). If the O2S signal is indicat-
ing a lean condition, the ECM will add fuel resulting in
fuel trim values above 128 (0% to 100%). If a rich condi-
tion is detected, the fuel trim values will be below 128
(0% to –100%), indicating that the ECM is reducing the
amount of fuel delivered. If exhaust emissions reach an
excessive level due to a lean or rich condition, a fuel trim
Diagnostic Trouble Code (DTC) is set.
Conditions for Setting the DTC
D No intrusive tests active.
D DTCs P0106, P0107, P0108, P0112, P0113, P0117,
P0118, P0122, P0123, P0125, P0131, P0132,
P0133, P0134, P0137, P0138, P0140, P0141,
P1167, P1171, P0201, P0202, P0203, P0204,
P0300, P0336, P0337, P0341, P0342, P0402,
P0404, P1404, P0405, P0406, P0443, P0506, and
P0507are not set.
D The average of short term fuel trim value is greater
than or equal to 120.
D Throttle Position (TP) is less than 95%.
D Engine speed is between 700 and 6000 rpm.
D Barometric Pressure (BARO) is greater than 92.0
kPa (10.4 psi).
D Coolant temperature is between 80°C (176°F) and
115°C (239°F).
D Manifold Absolute Pressure (MAP) is more than 90
kPa (10.2 psi).
D System is in closed loop.
D Adaptive index is ready.
Action Taken when the DTC Sets
D Emission related.
D "Armed" after two trip with a fail.
D "Disarmed" after one trip with a pass.
D MIL on if failure is detected in three consecutive trips.
D Stores a History DTC on the third consecutive with a
fail (The DTC will be armed after the second fail).
D Stores a Freeze Frame on the third consecutive trip
with a fail (if empty).
Conditions for Clearing the MIL/DTC
D The MIL will turn off after four consecutive ignition
cycles in which the diagnostic runs without a fault.
D A history DTC will clear after 40 consecutive warm up
cycles without a fault.
D DTC(s) can be cleared by using the scan tool.
Diagnostic Aids
Important: After repairs, use the scan tool Fuel Trim
Reset function to reset the long-term fuel trim to 128
(0%).
D Fuel pressure – The system will be lean if the pres-
sure is too low. It may be necessary to monitor fuel
pressure while driving the vehicle at various road
speeds and/or loads to confirm.
D Map sensor – An output that causes the ECM to
sense a lower than normal manifold pressure (high
vacuum) can cause the system to go lean. Discon-
necting the MAP sensor will allow the ECM to substi-
tute a fixed (default) value for the MAP sensor. If the
lean condition is gone when the sensor is discon-
nected, substitute a known good sensor and recheck.
D Fuel contamination – Water, in even small amounts,
near the in-tank fuel pump inlet can be delivered to
the injector. The water causes a lean exhaust and
can set DTC P0171.
Check for poor O2S or MAP sensor connection at the
ECM. Inspect the harness connectors for the following
conditions:
D Backed-out terminals
D Improper mating
D Broken locks
D Improperly formed
D Damaged terminals
D Poor terminal-to-wire connection
Inspect the wiring harness for damage. If the harness
appears to be OK, observe the O2S display on the scan
tool while moving the connectors and the wiring harness
related to the engine harness. A change in the display
will indicate the location of the fault.
Check the brake power booster check valve for possible
leaks.
DAEWOO M-150 BL2