LX450 low catalyst pressure, hard code set again

[Kasprzak]

Two weeks of trouble free driving and the darn check engine lights ups the low catlyst pressure bank one code again. Is it time to replace the cat or oxygen sensors? I have heard about both. I am waiting for my faithful members and their personal reccommendations.

 

[cruiserdan]

DTC code?

 

[MLX450]

How many miles? It might just be an O2 sensor.

 

[Kasprzak]

P0172, 125K on the mileage, has reset itself twice over a two week span. I do not notice any exhaust leaks, however at idle there is a rough spot it appears in the idle.(this goes away at driving speeds) Idle fluctuates between 1000 and then will drop quickly and roughly to 750 and then back up to 1000. Does anyone know of any good cruiser mechanics in the SLC or Ogden Utah Area? Could the poor idle and trouble code be interrelated? THanks in advance

 

[RavenTai]

again I have never heard of low catalist pressure, there is a code for low catalist effeciency but 172 is not it.

DIAGNOSTICS – ENGINE
DI–51
1996 LEXUS LX450 (RM482U)
DTC P0171 System too Lean (Fuel Trim)
DTC P0172 System too Rich (Fuel Trim)
CIRCUIT DESCRIPTION
Fuel trim refers to the feedback compensation value compared against the basic injection time. Fuel trim
includes short–term fuel trim and long–term fuel trim.
Short–term fuel trim 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 is overall fuel compensation carried out long–term to compensate for continual deviation
of the short–term fuel trim form the central value due to individual engine differences, wear over time and
changes in the usage environment.
If both the short–term fuel trim and long–term fuel trim are LEAN or RICH beyond a certain value, it is detected
as a malfunction and the MIL lights up.
DTC No. DTC Detection Condition Trouble Area
P0171
When air fuel ratio feedback is stable after engine warming up,
fuel trim is considerably in error on RICH side.
(2 trip detection logic)

Air intake (hose loose)

Fuel line pressure

Injector blockage, leak
P0172
When air fuel ratio feedback is stable after engine warming up,
fuel trim is considerably in error on LEAN side.
(2 trip detection logic)

Heated oxygen sensor (bank 1 sensor 1) malfunction

Mass air flow meter

Engine coolant temp. sensor
HINT:

When the DTC P0171 is recorded, the actual air–fuel ratio is on the LEAN side. When DTC P0172 is
recorded, the actual air–fuel ratio is on the RICH side.

If the vehicle runs shortage of fuel, the air–fuel ratio is LEAN and DTC P0171 is recorded. The MIL
then comes on.

If the total of the short–term fuel trim value and long–term fuel trim value is within +30 – –35 %, the
system is functioning normally.

If the vehicle runs shortage of fuel, the air–fuel ratio is LEAN and DTC P0171 is recorded. The MIL
them come on.
INSPECTION PROCEDURE
1 Check air induction system (See page DI–21).
NG Repair or replace.
OK
DI5L5–02
DI–52
DIAGNOSTICS – ENGINE
1996 LEXUS LX450 (RM482U)
2 Check for heated oxygen sensor (bank 1 sensor 1) data.
PREPARATION:
(a) Remove the fuse cover on the instrument panel.
(b) Connect the OBD II scan tool or LEXUS hand–held tester to the DLC3.
(c) Warm up the engine to normal operating temperature.
CHECK:
Read the heated oxygen sensor (bank 1 sensor 1) output voltage and short–term fuel trim.
RESULT:
Pattern Heated Oxygen Sensor (Bank 1 Sensor 1) Output Voltage Short–Term Fuel Trim
1 Lean condition (Changes at 0.55 V or less) Changes at about +20 %
2 RIch condition (Changes at 0.4 V or more) Changes at about –20 %
3 Except 1 and 2
3 Check for heated oxygen sensor (bank 1 sensor
1) (See page DI–47).
1, 2
3 Check fuel pressure (See page SF–17).
NG Check and repair fuel pump, pressure regulator,
fuel pipe line and filter (See page SF–6).
OK
4 Check injector injection (See page SF–20).
NG Replace injector.
OK
5 Check mass air flow meter and engine coolant temp. sensor (See page SF–34,
SF–58).
NG Repair or replace.
DIAGNOSTICS – ENGINE
DI–53
1996 LEXUS LX450 (RM482U)
OK
6 Check for spark and ignition (See page IG–1).
NG Repair or replace.
OK
Check and replace ECM (See page IN–27).

 

[Kasprzak]

I will have to double check the engine code, I was goine off memory. I don't have a reader and have to run it to autozone. The code is off again as my wife left a light on inside and killed the battery. So if it sets a third time, I will reread it and get a print out of the code. Thanks for the read out, if that is the case and that was the code, I now have step by step instructions how to fix it. A factory manual hasn't come accross my path yet. Just a cheesy one done by some college kid, that doesn't have any specifics. Thanks RavenTai!

 

[fzj80kidpen]

Kasprzak,
RavenTai hooked you up.
Now gets some LED's from George to take care of the wife killing the battery.