DI−84
DIAGNOSTICS − ENGINE
DIAP1−01
DTC P0171 System Too Lean (Bank 1)
DTC P0172 System Too Rich (Bank 1)
DTC P0174 System Too Lean (Bank 2)
DTC P0175 System Too Rich (Bank 2)
CIRCUIT DESCRIPTION
These DTCs indicate that the fuel is not enough (P0171, P0174) or too much (P0172, P0175). A DTC is set
when the smoothed fuel trim (short FT + long FT) reaches the malfunction limit. This limit is basically +35%
(too lean, adding fuel) or −35% (too rich, subtracting fuel). The values may vary with the emission limit for
each vehicle.
Fuel trim is related to the feedback compensation value, not to the basic injection time. Fuel trim includes
short term fuel trim and long−term fuel trim.
Short term fuel trim (short FT) is the short term fuel compensation used to maintain the air−fuel ratio at its
ideal theoretical value. The signal from the heated oxygen sensor indicates whether the air−fuel ratio is RICH
or LEAN compared to the ideal theoretical value, triggering a reduction in fuel volume if the air−fuel ratio is
RICH and an increase in fuel volume if it is LEAN.
Long term fuel trim (long FT) is overall fuel compensation carried out in long term to compensate for continual
deviation of the short term fuel trim from the central value, which is due to individual engine differences, wear
overtime and changes in the using environment.
DTC No. DTC Detecting Condition Trouble Area
S PCV valve and hose
S Mass air flow meter
Sum of short FT and long FT is more than 40% when following S Injector blockage
P0171 conditions are met (2 trip detection logic): S Fuel pressure
P0174 S Engine is warmed up. S Air induction system
S Closed loop S Heated oxygen sensor (bank 1, 2 sensor 1)
S Gas leakage in exhaust system
S ECM
S Mass air flow meter
Sum of short FT and long FT is below −35% when following S Injector leak or blockage
P0172 conditions are met (2 trip detection logic): S Ignition system
P0175 S Engine is warmed up. S Heated oxygen sensor (bank 1, 2 sensor 1)
S Closed loop S Gas leakage in exhaust system
S ECM
2003 LEXUS LS430 (RM988U)
Author: Date: 259
DI−85
DIAGNOSTICS − ENGINE
INSPECTION PROCEDURE
1 Confirm DTC.
(a) Save the freeze frame data.
(b) Clear the DTCs.
(c) Warm up the engine.
(d) Drive the vehicle for about 10 minutes.
(e) Make sure that the DTC is present.
NO Go to step 10.
YES
2 Check for exhaust gas leakage.
Check the leakage from the heated oxygen sensors.
NG Repair.
OK
3 Perform “A/F control” active test to check oxygen sensor operation.
(a) Warm up the engine.
(b) On the hand−held tester, select “A/F CONTROL” from the active test menu.
(c) Switch the injection volume between +25% and −12.5%.
OK:
Injection Volume O2S B1S1, O2S B2S1
+25% > 0.5 V
−12.5% <0.4 V
NG Replace heated oxygen sensor.
OK
2003 LEXUS LS430 (RM988U)
Author: Date: 260
DI−86
DIAGNOSTICS − ENGINE
4 Check PCV valve and piping leakage (see page EC−5).
NG Repair.
OK
5 Check leakage between air cleaner and intake manifold.
NG Repair.
OK
6 Visually check mass air flow meter.
(a) Remove the mass air flow meter.
(b) Check if the foreign matter like lint sticks to the sensor ele-
ment.
NG Clean sensor element. If necessary, replace
mass air flow meter.
OK
7 Check for spark and ignition.
NG Repair.
OK
2003 LEXUS LS430 (RM988U)
Author: Date: 261
DI−87
DIAGNOSTICS − ENGINE
8 Check fuel pressure (see page SF−5).
NG Check fuel pump, fuel line fuel filter and pres-
sure regulator.
OK
9 Check injector for blockage or leakage (see page SF−23).
NG Replace injector.
OK
Replace ECM (see page SF−86).
10 Check if vehicle has run out of fuel recently.
NO Go to step 11
YES
DTC was set by running out of fuel.
2003 LEXUS LS430 (RM988U)
Author: Date: 262
DI−88
DIAGNOSTICS − ENGINE
11 Perform driving pattern.
(a) Turn the ignition switch OFF.
(b) Start the engine and warm up the engine until the coolant temp reaches 75°C (167°F).
(c) On the hand−held tester, select “CHECK MODE”.
(d) Drive the vehicle at 30 km/h (20 mph) or faster for at least 3 minutes.
(e) Stop the vehicle and allow the engine to idle for at least 2 minutes.
(f) Repeat (e) and (f) twice.
(g) Check DTCs.
Result:
Is DTC P0171, P0172, P0174 or P0175 present?
NO Perform test drive according to customer inter-
view and freeze frame data til the DTC is set.
YES
Go to step 2.
2003 LEXUS LS430 (RM988U)
Author: Date: 263
