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1997 Seville STS
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14 Posts
Discussion Starter · #1 ·
I have recently replaced the head gaskets and installed the Timesert inserts and I am coming up with all O2 sensors as well as the G0109. I located and attatched the ground and the car would not start. I took off the ground and it starts and runs fine yet I still get the SES and O2 codes. Can someone help? I just need to clear this issue up to smog and tab it. I have also checked for air leaks and there are none. Thank you very much for any help.
 

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1997 Seville STS
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14 Posts
Discussion Starter · #4 ·
P0135 HO2S heater circuit bank 1 sensor 1(replaced), p0141 HO2S heater circuit bank 1 sensor 2, P0147 HO2S heater circuit bank 1 sensor 3, P0155 HO2S heater circuit bank 2 sensor 1 (replaced), these are current. I have 2 codes in history, they are P0325 Knock sensor circuit and P0603 PCM memory rest.
 

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'98 STS (RIP @ 206,xxx miles)
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4,854 Posts
Since all of your O2 sensor codes relate to the "heater" performance, have you checked the fuses labeled as OXY SEN 1 and OXY SEN 2 in the engine compartment fuse/relay box? Both 10 A (blue).
 

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1997 Seville STS
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14 Posts
Discussion Starter · #6 ·
Yes I have and they are good. Is there any other options. I have read many of your postings and you seem like a very knowledgeable person, especially on the cadillacs. Any help will be greatly appreciated. Whats your take on the G0109? It came up once before but not since. Plus I connected it and it wouldn't start. It cranked and tried but no start and it drained the battery real fast. Disconnected it works fine and now it doesn't come up with the code G0109.
 

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'98 STS (RIP @ 206,xxx miles)
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4,854 Posts
Yes I have and they are good. Is there any other options.
Ninety percent of the time a visual inspection of a fuse is conclusive. The remaining 10% will require an ohmmeter test for confirmation. And that is an unforgettable lesson to learn the "hard way".

....Whats your take on the G0109?
I have no idea what G0109 means. That is not an OBDII diagnostic trouble code in my experience; where did you see this?
 

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1997 Seville STS
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14 Posts
Discussion Starter · #9 ·
I am wrong, it was something I saw a while back. I know it has to do with the ground off the rear of the bank 2 head near the transmission slector control. Have you heard of an issue with this?
 

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1997 Seville STS, 2000 Seville STS
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1,694 Posts
G109 is the common ground point for all 4 of your O2 sensor heaters. It is the only common point that if disconnected from the engine (think it goes on a double nutted stud on the end of the rear head under the master cylinder) that will take out all 4 of your O2 sensors. If that ground connection is not grounded then none of the heaters will work and you will set those 4 codes.
 

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1997 Seville STS
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14 Posts
Discussion Starter · #11 ·
Thank you Mark, thats what I thought. But why when its connected does it not start? It tries but wont start and it drains the battery very fast. Any ideas?
 

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1997 Seville STS, 2000 Seville STS
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1,694 Posts
You are probably missing some other ground, or grounds on the engine block. There should be one down on the front of the engine under the water pump, near the transmission flange, and another on the rear passenger side corner of the block just above the transmission support bracket. The most important ground is the big black wire from the ICM under the ignition coils to one of the rear valve cover bolts right on top of the engine.
 
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