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1996 STS Oxygen Sensor Codes; Is is the Sensors?


acel

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I have a 1996 STS with 118,000 miles on it. It was driving perfect and then about 2 weeks ago, the check engine light came on and a "Service Emissions System" message scrolled across the panel. I checked the codes and I got P0135 (Bank #1, Sensor #1), P0141 (Bank #1, Sensor #2), and P0155 (Bank #2, Sensor #1). Why would they all come on at once?

I had noticed that the car is starting harder than normal over the past few months. The last time that happened, it turned out to be a fuel pressure regulator (I remember smelling gas when I disconnected the vacuum line from it). Could that same problem be happening again and causing the O2 sensors to trigger?

BTW, I checked both O2 sensor 10A fuses and they're fine.

Any suggestions? I hate to have to buy three sensors.

acel

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I would clear the codes and test drive the car. If the same message appears, check the codes again.

The OBD system was pretty good in '96, but far from 100% accurate and subject to interpretation.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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This is unusual. I have a 96, I will do some research on this. Its not likely a common ground due to the front bank rear bank O2 sensors. Was any additive used or non standard fuel? Could silicone have gotten into the intake manifold?

See this:

What will damage my O2 sensor?

Home or professional auto repairs that have used silicone gasket sealer that is not specifically labeled "Oxygen sensor safe", "Sensor safe", or something similar, if used in an area that is connected to the crankcase. This includes valve covers, oil pan, or nearly any other gasket or seal that controls engine oil. Leaded fuel will ruin the O2 sensor in a short time. If a car is running rich over a long period, the sensor may become plugged up or even destroyed. Just shorting out the sensor output wire will not usually hurt the sensor. This simply grounds the output voltage to zero. Once the wiring is repaired, the circuit operates normally. Undercoating, antifreeze or oil on the *outside* surface of the sensor can kill it.

See this article

http://www.mr2.com/TEXT/O2_Sensor.html

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I would clear the codes and test drive the car. If the same message appears, check the codes again.

The OBD system was pretty good in '96, but far from 100% accurate and subject to interpretation.

Jim,

I cleared the codes a few days after they appeared but it only took about 2 hours before the same three showed up again.

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Highly unlikely to have 3 O2 sensors fail at the same time. Also it has nothing to do with the O2 sensers, rather the O2 sensor heater circuits seem to be the issue.

DTC P0135 HO2S Heater Performance Bank 1 Sensor 1

DTC P0141 HO2S Heater Performance Bank 1 Sensor 2

DTC P0155 HO2S Heater Performance Bank 2 Sensor 1

2 different fuses are used for the heaters, but all share the same ground. Ground G109.

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This is unusual. I have a 96, I will do some research on this. Its not likely a common ground due to the front bank rear bank O2 sensors. Was any additive used or non standard fuel? Could silicone have gotten into the intake manifold?

See this:

What will damage my O2 sensor?

Home or professional auto repairs that have used silicone gasket sealer that is not specifically labeled "Oxygen sensor safe", "Sensor safe", or something similar, if used in an area that is connected to the crankcase. This includes valve covers, oil pan, or nearly any other gasket or seal that controls engine oil. Leaded fuel will ruin the O2 sensor in a short time. If a car is running rich over a long period, the sensor may become plugged up or even destroyed. Just shorting out the sensor output wire will not usually hurt the sensor. This simply grounds the output voltage to zero. Once the wiring is repaired, the circuit operates normally. Undercoating, antifreeze or oil on the *outside* surface of the sensor can kill it.

See this article

http://www.mr2.com/TEXT/O2_Sensor.html

I've used the same fuel since purchasing the car in 1999 (never an additive). As far as the intake manifold, that's easy to answer. I bought the car with 41,000 miles on it and noticed accessive oil consumption right away (about 1 quart per 300-400 miles). Cadillac determined it needed a new engine (most cylinders were 0.002" oversized) and since I had an extended bumper-to-bumper warranty ($0 deductable), one was installed at around 50,000 miles. It's been darn near perfect since then.

The only other work that was done recently that might have contributed to this condition was the installation of a new turbine speed sensor in the transmission (shop did that) and a new gas tank filler neck (did that one myself).

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It is not the O2s...its the O2 heater circuits. See post above..Inspect Ground G109.

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It is not the O2s...its the O2 heater circuits. See post above..Inspect Ground G109.

Could you please provide some assistance in this area. I don't have the shop manuals so I'm not sure where G109 is located. Thanks for your patience, though.

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It is not the O2s...its the O2 heater circuits. See post above..Inspect Ground G109.

Could you please provide some assistance in this area. I don't have the shop manuals so I'm not sure where G109 is located. Thanks for your patience, though.

All I have is the GM online service manual. Guess what...it goes back to 1998. Pre 1998 is weak..most of the powertrain info is there....but not like the 1998 and newer cars. I also have '93-'94 factory service manuals...but the '93-94 cars are wired different then the '96-97 ones due to OBDII.

I was able to attach the 1996 PO135 O2 heater circuit diagram. It shows G109. All 3 codes use the G109 ground.

Someone with a 1996 or 1997 STS manual should be able to look up where G109 is...

post-2-1189225813_thumb.jpg

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Highly unlikely to have 3 O2 sensors fail at the same time. Also it has nothing to do with the O2 sensers, rather the O2 sensor heater circuits seem to be the issue.

DTC P0135 HO2S Heater Performance Bank 1 Sensor 1

DTC P0141 HO2S Heater Performance Bank 1 Sensor 2

DTC P0155 HO2S Heater Performance Bank 2 Sensor 1

2 different fuses are used for the heaters, but all share the same ground. Ground G109.

Very Cool Logan, I should have confirmed the codes

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Fisher...

Did you see this?

"Someone with a 1996 or 1997 STS manual should be able to look up where G109 is..."

You have '96 Helm factory manual?

Here is the PO141 diagram..

post-2-1189226836_thumb.jpg

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Fisher...

Did you see this?

"Someone with a 1996 or 1997 STS manual should be able to look up where G109 is..."

You have '96 Helm factory manual?

Here is the PO141 diagram..

I didn't see this before Logan, I just got home at 2:45 AM here is the location of G109

Left hand rear corner of the engine, near the park/neutral position switch

Here is the location in the manual

8A-201-17, Fig 34

post-2998-1189234824_thumb.jpg

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks for all your help guys. I'm going to check the ground connection out this morning. Looks very promising.

I guess I should have invested in the manuals. I had both for my old '79 Eldorado (still have 'em I think) and should have learned from experience.

Dave (acel)

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Thanks for all your help guys. I'm going to check the ground connection out this morning. Looks very promising.

I guess I should have invested in the manuals. I had both for my old '79 Eldorado (still have 'em I think) and should have learned from experience.

Dave (acel)

Check ebay and www.helpinc.com for the manual.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks Fisher. I'll do that.

I just spent 20 minutes looking for the ground wire and had no luck. I found all 4 O2 sensors easily and I see where they all share the same wiring harness. I don't see a single wire coming out of the harness going to the engine or body in the lower left side (driver's side) of the engine. Should I be looking under shrouds? Will it simply be a wire stake bolted to the engine or frame? Sorry for being a pest.

acel

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Ill pull out my manual in a bit and see what I can find

Dont know where Fisher is with the picture...

I found a pic of 'a' G109 in the '94 book today. Dont know if it is the same G109 on the '96. This G109 appeared to be mounted on a stud, stud screwed into the end of the cylinder head, near the coolant sensor, on the drivers side, rear cylinder head.

The wiring changed a bunch between '94 and '96 for OBDII. May not be the same G109. I attached a picture from a 1998 Deville. My 1994 book shows G109 near item #7.

post-2-1189312430_thumb.jpg

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Wow Logan you are taking shots at me, rightfully so, but darn :lol:

Anyway, let me explain why this process is taking longer than usual. I dont have a digital copy of the manual, only the of the drivetrain. I sat down before and I found the ground G109 in my manual after some searching, looked at the fault tree, etc. Now I have to unpack the scanner because it is packed, and hook it up to my laptop, scan the photo on the couch, edit it, upload it to Photobucket, and do the post. Its an exhausting process, :lol: I know I know a man with excuses is an excuse of a man.

Here is the scan of G109's location, pay attention to S127 also, see the second scan. S stands for splices. I would have a look at S127 also.

G109.jpg

According to the manual, S127 is located in the engine harness, approximately 10 cm from G109 conn breakout, see pic

G109schematic.jpg

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