O2 Sensor & SES Light

OK, so the 99 Intrigue with the 3800 and about 168K tripped the SES light recently. Had the codes read at Autozone, with the O2 sensor (pre-Cat) and the Gas Cap being the culprits.

Gas cap was actually off, so that solved that dilemma.

Ordered an O2 sensor and installed it yesterday. Went back to Autozone and had the codes cleared. Drove the car a few miles and the SES light came back on. Had the codes read again and the O2 code was back. Cleared it again and it came back once more.

Any clue what might be going on other than possibly a bad sensor? Kind of stumped here. :runaround: Thanks.

Smitty's Buick

What exactly did the code read? Many times when the ECU complains about sensor readings being out of range it's not the sensor itself that's gone bad.

I had the codes read again today. The only code pulles was P0134 - O2 Sensor Circuit No Activity Detected (Bank I Sensor 1).
Smitty's Buick

Here is an excerpt from an article I found online:

t's important to know how the O2 sensors are identified because a diagnostic trouble code that indicates a faulty O2 sensor requires a specific sensor to be replaced. Bank 1 Sensor 1 might be the back O2 sensor on a transverse V6, or it might be the one on the front exhaust manifold. What's more, the O2 sensors on a transverse engine might be labeled differently than those on a rear-wheel drive application. There is not a lot of consistency as from one vehicle manufacturer to another as to how O2 sensors are labeled, so always refer to the OEM service literature to find out which sensor is Bank 1 Sensor 1 and which one is Bank 2 Sensor 1. This information can be difficult to find. Some OEMs clearly identify which O2 sensor is which but others do not. If in doubt, call a dealer and ask somebody in the service department.

In case you didnt know, you have a V6 transverse engine. Its a possibility that you replaced the wrong sensor, I think you should call or stop by a GM dealership and see what they have to say, be prepared though about dealerships, some will be ready and willing to help you out, some will be complete a-holes and wont say boo without some money.

Also, heres a link with more info about your code, if youll notice, it says its the front sensor, which just goes to show how accurate the excerpt is about things being inconsistent:
http://www.obd-codes.com/p0134

I checked the voltage at the sensor and have a good 12V reading. When I started the car, the voltage at the other wires (non-12V, non-Ground) started at .1V and climbed to .9V where it sat for a minute or so before climbing to 5V - 5.5V. According to the Haynes manual, the voltage should be .1V to .2V in the first minute or two, and then fluctuate between .1V to .9V. So, it appears I have too much voltage coming out of the O2 sensor, throwing the code. Is the new O2 sensor bad, or is something else contributing? Any other ideas to try? Thanks in advance.
Smitty's Buick

I checked the voltage at the sensor and have a good 12V reading. When I started the car, the voltage at the other wires (non-12V, non-Ground) started at .1V and climbed to .9V where it sat for a minute or so before climbing to 5V - 5.5V. According to the Haynes manual, the voltage should be .1V to .2V in the first minute or two, and then fluctuate between .1V to .9V. So, it appears I have too much voltage coming out of the O2 sensor, throwing the code. Is the new O2 sensor bad, or is something else contributing? Any other ideas to try? Thanks in advance.
Smitty's Buick

I would take readings of the O2 sensor of the other bank and see how they differ. I'd also, if possible, swap the sensors between the cylinder banks and see if the code would follow the location change.

When you took the sensor voltage reading, did you take the reading across the two sensor wires (i.e. non-GND, non-12V), or did you take it between the chassis ground and the sensor wires? The 0.1V-0.9V range mentioned in the manual is supposed to be refering to the voltage differential between the two sensor wires.

Thanks for the clarification, canatto. I went back and measured the voltages as you suggested. I started with the post-cat sensor and went to the pre-cat sensor. (This car only has the two sensors. It sounds like there are others that have one for each side of the engine as well as maybe one downstream.)
Post-Cat: .4V at inital startup
Increased momentarily to .6V
Dropped to .14V
Increased to .88/.90V where it seemed to stay while the engine idled
Pre-Cat: .88/.93V at initial startup
Dropped quickly to .04/.05V where it seemed to stay while the engine idled

I measured the resistance across the two pins (heater) of the two sensors as well as the one I removed. According to Haynes, normal is between 5 and 7 ohms.
Post-Cat: 6.3 ohms
Pre-Cat: 7.6 ohms
Old Sensor: 4.6 ohms

It looks like the sensor I took out had low resistance which I guess is what caused it to be faulty. The new sensor has too high of resistance and low voltage.

Is it safe to assume that is the reason for the low voltage while running (.05V vs .10V minimum)?

Smitty's Buick

http://www.carcare-tips.com/oxygen-sensor-article.html
The Inside Story on Your Car's Oxygen Sensor


The most over sold, unnecessary item to fly off the shelves of auto parts stores, are oxygen sensors.

Most O2 codes I've seen have been due to bad/corroded/cut wiring or some other issue upstream.

The O2 sensors are measuring the end result.

pfofit -
What other things have you seen other than wiring to throw the O2 sensor code? The car runs fine, the mileage seems a little low, but nothing outrageous (24 - 26 MPG highway). It will never be as good as my Park Ave at 28 - 30 MPG. Any ideas to check??? Thanks.
Smitty's Buick

........Is it safe to assume that is the reason for the low voltage while running (.05V vs .10V minimum)?

Smitty's Buick

The heater element and the sensor circuit are supposed to be isolated from each other in an O2 sensor, and the heater element resistence has little, if not nothing, to do with the sensor output. You should be able to prove this by disconnecting the sensor connector and measuring the resistence between a heater wire and any of the sensor output leads. The measured resistence should be close to infinite on a multimeter, or at least in multi mega ohm range.

Now it seems that your precat sensor reads a extremely rich fuel/air mixture while the post-cat reads extremely lean. I would suspect something else than the sensor itself, given that the brand new sensor yielded the same DTC code. Perhaps you could possiblly open a major vacuum line, brake booster hose for example, and see if there is any changes in the sensor output (pre-cat and post-cat), in a fully warmed-up condition, so as to determind the sensors do indeed reponde to fuel-air mixture?

I'm taking the easy way out (for the moment). :uhoh: I am sending the new sensor back to RockAuto for a replacement. In the mean time, I put the original sensor back in. The voltage across sensor reads over 14V. Sounds like an internal short. When the replacement sensor comes back, I will replace it and see if that solves the problem. I will update the post then.
Smitty's Buick

Update - The SES light went out.... Can't explain that! Looking forward to getting the new sensor from RockAuto and see how that goes. :naughty:

Smitty's Buick