New owner; O2 sensor problem?
Thread Starter
Pit Crew
Joined: Dec 2016
Posts: 123
Likes: 37
From: Lourinhã
New owner; O2 sensor problem?
Hello all,
Just took delivery of my new 240k miles SC430.
It hasn't been used for a year so MOT expired.
Lexus service history up until 235k miles.
I am now getting it ready for MOT; there used to be a CEL caused by P0171 and P0174 which I seem to have cured by cleaning the MAF, after which I tested it as per workshop manual. Both temp. and airflow measurement ok. Also reset the ECU
There's still a rough idle and I got below measurements.
Do I have 2 defective O2 sensors?
O2 FT B1 S1 19,71%
O2 FT B1 S2 99,15%
O2 FT B2 S1 15,59%
O2 FT B2 S2 99,15%
O2 S B1 S1 0,05V
O2 S B1 S2 0,8V
O2 B2 S1 0,1V
O2 B2 S2 0,09V
Fuel Sys #1 en #2 CL
Short FT 1 19,5%
Long FT 1 28,8%
Short FT 2 19,5%
Long FT 2 29,6%
Thanks in advance,
Cheers,
Johan
Just took delivery of my new 240k miles SC430.
It hasn't been used for a year so MOT expired.
Lexus service history up until 235k miles.
I am now getting it ready for MOT; there used to be a CEL caused by P0171 and P0174 which I seem to have cured by cleaning the MAF, after which I tested it as per workshop manual. Both temp. and airflow measurement ok. Also reset the ECU
There's still a rough idle and I got below measurements.
Do I have 2 defective O2 sensors?
O2 FT B1 S1 19,71%
O2 FT B1 S2 99,15%
O2 FT B2 S1 15,59%
O2 FT B2 S2 99,15%
O2 S B1 S1 0,05V
O2 S B1 S2 0,8V
O2 B2 S1 0,1V
O2 B2 S2 0,09V
Fuel Sys #1 en #2 CL
Short FT 1 19,5%
Long FT 1 28,8%
Short FT 2 19,5%
Long FT 2 29,6%
Thanks in advance,
Cheers,
Johan
Pole Position
Joined: Dec 2009
Posts: 3,135
Likes: 276
From: CA - San Diego
Sometimes cleaning the MAF sensor does not resolve the problem. Check this thread: https://www.clublexus.com/forums/sc4...ot-steady.html
Pole Position
Joined: Dec 2009
Posts: 3,135
Likes: 276
From: CA - San Diego
The DTCs indicate Lean mixture
The voltage in B1 S1 is low assuming engine idle greater than, or equal to 1500RPM. B1 S2 has marginal voltage both should be at 1.0volts
other suspect areas:
The voltage in B1 S1 is low assuming engine idle greater than, or equal to 1500RPM. B1 S2 has marginal voltage both should be at 1.0volts
other suspect areas:
- PCV hose connection
- Mass air flow meter (previous post)
- exhaust leak
Racer
Joined: Oct 2015
Posts: 1,810
Likes: 170
From: Colorado
Now you need to check the fuel trims at 2500 rpm's. This will tell us if it's a vacuum leak, or we need to look at other things. This is not a O2 issue.
oh, and make sure your pulling those numbers with the engine at temperature. Give us the short and long fuel trim percentages at the higher rpm.
oh, and make sure your pulling those numbers with the engine at temperature. Give us the short and long fuel trim percentages at the higher rpm.
Last edited by Coleroad; Feb 23, 2018 at 03:50 PM.
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Lexus Test Driver
Joined: Dec 2014
Posts: 8,213
Likes: 949
From: Fl
You should also check all of the rubber vacuum lines. All are suspect on our cars due to age.
I found several that were cracked causing vacuum leaks.
dont ignore it...you may end up replacing good parts.
I found several that were cracked causing vacuum leaks.
dont ignore it...you may end up replacing good parts.
Racer
Joined: Oct 2015
Posts: 1,810
Likes: 170
From: Colorado
yeah bgw, I would bet he has one or more vacuum leaks. The op comes back with the fuel trim percentages at the higher rpm. we'll know for sure just from that. It's awesome the op came with all the information he did. It makes it really easy to narrow the problem down . If it is a vacuum leak, he'll be able to know if he fixed all of the vacuum leaks too. All he'll need to do is look at the fuel trim percentages again at both idle and the higher rpm. Fuel trim is a great diagnostic tool.
Pole Position
Joined: Dec 2009
Posts: 3,135
Likes: 276
From: CA - San Diego
For those who would like to learn more about ‘Fuel Trims’ here’s a link to some basic information:
Basic Understanding of Fuel Trim Percentages
Basic Understanding of Fuel Trim Percentages
Lexus Test Driver
Joined: Dec 2014
Posts: 8,213
Likes: 949
From: Fl
yeah bgw, I would bet he has one or more vacuum leaks. The op comes back with the fuel trim percentages at the higher rpm. we'll know for sure just from that. It's awesome the op came with all the information he did. It makes it really easy to narrow the problem down . If it is a vacuum leak, he'll be able to know if he fixed all of the vacuum leaks too. All he'll need to do is look at the fuel trim percentages again at both idle and the higher rpm. Fuel trim is a great diagnostic tool.
Racer
Joined: Oct 2015
Posts: 1,810
Likes: 170
From: Colorado
that's one of many possibilities for a vacuum leak. Other things even as simple as the oil fill cap not on good. The oil dipstick not seated. Intake tube between the maf and the throttle body. Throttle body gasket, intake gasket. Any vacuum line, any leak in the pcv system. If it had a plastic intake you would have to inspect it for crakcks. 240 thousand miles none of the above would surprise me. With a total fuel trim percentage of almost 50%, I'm surprised it even idles.
Last edited by Coleroad; Feb 24, 2018 at 09:06 AM.
