Mechanics

TROUBLE CODES PO133 & PO141

1997 Saturn SC2

Computer problem
1997 Saturn SC2 4 cyl Front Wheel Drive Manual 119000 miles

Hi all, new member here. Recently bought a '97 SC2 1.9L 5spd 119K miles. And have to pass emissions to register it. Car runs good, but MIL light is on and throws codes PO133 & PO141:

O2 Sensor circuit slow response b1s1
O2 Sensor Heater circuit b1s2

I have AutoTap's diagnostic tool and have checked the IAT sens and ECT sensor. Both are operating properly. O2 sens b1s1 in the exhaust manifold oscillates, but does not hit the recommended low/high voltage output of.2 & .8 volts (should be replaced, but it's working) - O2 sens b1s2 behind the cat. Starts out with a voltage output of ~.7 volts (cold start), oscillating +/- 100 mV or more. As the engine & cat begin to warm (at idle), voltage output slowly drops. Getting as low as.35 volts (oscillating between.3 & .4 volts). Revving the engine to 2000 rpm and holding - the voltage slowly drops to a mere 150 mV and stays there. Even when rpm's are returned to idle.

From what I have found online, it appears that O2S B1S2 behind the cat should start out at a higher voltage of.8 to 1 volt, (cold start/rich condition), then as the engine/cat/sensor warms to operating temperature, the voltage should drop to approx.45 volts and stay in that range rather steadily (no wild fluctuation/oscillating as is the case with O2S B1S1 in the manifold).

Since my downstream Heated O2 sensor is oscillating (which it should not be doing AFAIK.) And, it's voltage output steadily drops, eventually leveling off at a mere 150 mV (instead of maintaining a fairly steady.45'ish volts). Do I replace this sensor first? Or could something else be giving me these readings? Bad cat perhaps? Or, could B1S1 be skewing S2's readings? Or, is there something else I am not thinking of, or aware of that I should be testing/looking at?

As I said - Engine temp sens & Intake air temp sens are working properly. MAP appears to be good. Fuel trim appears to be within proper limits.

If the cat were bad, wouldn't I get codes specific to the cat? (An oscillating O2 B1S2 can be an indication of a bad cat.)

My gut says replace S2 first. Then reset the MIL. See what happens. What do you all think?

I'm kinda missing those old CTO switches and vacuum operated emissions controls of yester-years lol.
Avatar
Jd512k
March 24, 2010.



Try this under the intake manifold there's a couple of tan wires that have round eye let's that's suposed to be bolted to the block that's the grounds for ur o2 sensors see if there good and tight. Let me know what u find.

Saturntech9
Mar 25, 2010.
Thanks. I'll take a look at those grounds tomorrow. I've ordered a new front O2 sensor. I hooked up my laptop to the vehicle using AutoTap scanner. Logged about 20 minutes of OBDII data - from cold start to fully warmed up - at idle and at ~2000 rpm. Have spent the past two days looking at every piece of data on every sensor. It all looks good except for the O2 sensors. Are these O2 grounds on the back side (firewall side) of the engine block?

Tiny
Jd512k
Mar 25, 2010.
Those grounds are under the intake manifold bolted right to the engine block on the firewall side of block. If u take off the air intake tube on the throttle body remove it and look under the intake manifold it's closest to the drivers side. Let me know what u come up with.

Saturntech9
Mar 25, 2010.
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Removed the air intake tube. There is an eyelet w/ four wires bolted to the block beneath #4 intake, and a few inches above the starter. It is nice and tight. Do not see any other grounded wires/eyelets in the vacinity.

Tiny
Jd512k
Mar 27, 2010.
Sounds like u found the grounds and they sound like there attached.heres some info on ur codes and a trouble tree for ur p0141.let me know what u find there u could just have a couple of bad o2 sensors.the fronts going bad are pretty common.


http://www.2carpros.com/forum/automotive_pictures/416332_img005_1.jpg



http://www.2carpros.com/forum/automotive_pictures/416332_img006_2.jpg


Saturntech9
Mar 28, 2010.
Thanks! Appreciate the info! The documents are too small/blurry for me to read though? Can you email them, or post them bigger?

I posted a video on youtube - it's an graph using AutoTap and my laptop of both the O2 sensors, engine temp, engine rpm. Shows the voltage output of both sensors from cold start - idle - 2000 rpm - fully warmed up - back to idle.

If you search my name " jd512k" or " 1997 Saturn O2 Sensor" you should be able to find the video and see first hand what the sensors are doing.

Tiny
Jd512k
Mar 28, 2010.
Private message me ur email I'll email u those pages. Ur front o2 sensor is probably bad real common for those to go bad. Not as common for ur rear one to go bad but there's a trouble tree for ur rear o2 sensor follow it. Let me know what u find.

Saturntech9
Mar 28, 2010.
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2CarPros is not letting me PM you - I don't have 10 posts yet. My email is the same user name as on here - but at yahoo

Really appreciate the help with this!

Tiny
Jd512k
Mar 28, 2010.