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George H.
George H., ASE Certified Technician
Category: Saturn
Satisfied Customers: 816
Experience:  ASE Master Tech 15+ Years
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I have a 1995 Saturn SC-1 with a 5-speed manual trans.It

Customer Question

I have a 1995 Saturn SC-1 with a 5-speed manual trans.It came from the factory with a SOHC 1.9liter engine but the engine was swapped out for a Saturn DOHC 1.9liter engine.I don't know what year model the engine is,it was in the car when i got it.My problem is the o2 sensor circuit is reading to high of voltage at the harness side of the o2 (oxygen sensor) circuit,it has a voltage reading of 0.97 volts but the Chilton repair manual says it should be 0.5 volts or less with the key on and engine not running.The service engine light is on and it has a code 13 stored,the car runs real sluggish and want pass an inspection.I've replaced the o2 sensor (3-times),knock sensor ,spark plugs,wires,coils,ignition module,catalytic converter,ECM/PCM (4-different ones,2-for 95 5-speed SOHC and 2-for 5-speed DOHC engines),fuel filter,gas cap just to name some of the things that's been done to the car.One thing that may have something to do with the o2 circuit being out of whack is i started the car with the jumper in the OBD I port ( i was checking to see if any codes were stored)and it blew out the service engine light,when i replaced the bulb it had a trouble code 13 stored in it.Please help me find my problem!
Submitted: 4 months ago.
Category: Saturn
Expert:  Barry Sergeant replied 4 months ago.

Hi, my name is Barry. Welcome to Just Answer. I would be happy to help you with your Saturn SC-1. I believe that has a one wire o2 sensor. Are you comfortable testing a few wires with a DVM?

Customer: replied 4 months ago.
it is a one wire o2 sensor car,and i'm comfortable doing some testing with my DVM.Just tell me what you need me to do,i have some mechanical skills so i can do what you need me to.
Expert:  Barry Sergeant replied 4 months ago.

Ok. Unplug the o2 sensor and the connectors on the pcm.

We need to test the wire connector for the o2 sensor vehicle side for continuity to ground and for dc voltage.

Customer: replied 4 months ago.
Sorry it's taken me so long to get back to you,but i'm ready to run those checks and tests with the multimeter.Just let me know what you need me to do.
Expert:  Barry Sergeant replied 4 months ago.

No problem.

Unplug the o2 sensor and the connectors on the pcm.

We need to test the wire connector for the o2 sensor vehicle side for continuity to ground and for dc voltage.

Expert:  Barry Sergeant replied 4 months ago.

Set the dvm to ohms.

Test the vehicle side of the o2 sensor wire to the ground terminal on the battery.

What does it read?

Then set the dvm to dc volts. Turn the key to the on position. Do the same test as above between the o2 connector and negative battery terminal.

What does it read?

Customer: replied 4 months ago.
I did the ohms test first and there was no reading at all,then i did the DC voltage test from the o2 connector to the ground and there was a reading of 0.981 volts.The chilton manual says it should have a reference reading of 0.5 volts.
Expert:  Barry Sergeant replied 4 months ago.

Did you perform the test with the pcm disconnected?

Customer: replied 4 months ago.
I performed it with it connected.
Expert:  Barry Sergeant replied 4 months ago.

Try it with the pcm disconnected. I want to see if the pcm is making the voltage or if the wire is shorted to power somewhere.

Customer: replied 4 months ago.
With the pcm disconnected and with the key on i'm getting a reading of 01.2 volts and with the key off it's reading 00.1volts.
Expert:  Barry Sergeant replied 4 months ago.

Ok. There is a short to voltage somewhere in that wire. You can try to locate the short or you can run a new wire from the O2 sensor to the pcm.

Customer: replied 4 months ago.
That's what i was thinking when i saw what it was reading.When i first discovered the o2 sensor connector was reading to high,one of the things i checked was the reading at the pcm harness.I'm going to run a new separate wire out to the o2 sensor and see what it reads.But i think what's going to need to be done is figure out which one of the wires the o2 sensor wire get it's voltage from.I'm talking about the wire or wires that sends the voltage to the pcm itself.I can maybe figure out a way to reduce it's voltage.But anyway i have a pressing matter i have to take care of,I'll let you know how things turn out tomorrow.
Expert:  Barry Sergeant replied 4 months ago.

I think your on the right track. Just let me know how it goes tomorrow.

Customer: replied 4 months ago.
Sorry i didn't get a chance to get back with you earlier today,but i cut the wire that runs from the o2 sensor harness to the pcm about 1" from the connector that goes in the pcm and i took a voltage reading there and i'm still getting the same reading(0.981volts).I then pulled every single fuse on the car(under hood and passenger compartment) one at a time while checking the voltage from the o2 sensor wire and the voltage stayed the same except when i removed the fuses for the pcm and ign.I think one of the wires on the harness is supplying to much voltage somehow for some reason.How do you think we can go about figuring out what's the problem?
Expert:  Barry Sergeant replied 4 months ago.

It sounds like the short to voltage is internal to the pcm.

Customer: replied 4 months ago.
I have (4) four different pcm's and i've tried them all and get the same voltage reading at that wire,and i'm talking about at the pcm connector with the wire cut so it's not picking up any voltage in the harness.
Customer: replied 4 months ago.
What do you suggest now?
Expert:  Barry Sergeant replied 4 months ago.

There is most likely a short to power going to the pcm on another pin. There shouldn't be any voltage on the o2 sensor pin on the pcm with the o2 sensor unplugged. I would start testing the wiring to the pcm for power. Let me know what wires have power on them and maybe we can find your issue.