My car set a code yesterday. Its a 2004 GTO, meaning that its an LS1. I need a little guidance. I know the 171 means lean left bank, and that the 131 code means there is low voltage from the upstream O2. The motor is missing badly and started out of nowhere. It was intermittent at first and would run smooth momentarily and then erratic until it finally remained erratic on the drive home.

I know, check the wires and if OK change the O2. But, this is the third left bank 02 problem I've had in the last 5 years. It seems every other year I have to change the left O2. One time it was the wire, and twice it was the O2. Any suggestions are appreciated.

 

Check ALL grounds and connections. In your case mainly the grounds where they screw down to the chassis, block, or body. Corrosion can rear its ugly head where the connection might appear good.

 

Yea OK. Which ground in particular does the 02 circuit use? I had a problem with the strap going to the rear of the left cylinder head earlier this year, but I fixed it. It didn't affect motor performance, but I noticed it was broken.

 

UPDATE:

I went to work today and started the car when I got home. I cleared out the codes and then did a rescan. The rescan showed no codes, so I started the motor. It ran well for about 10 minutes until it warmed up. Then it started to miss so I shut it off. Did a rescan again and had no codes. Restarted it a third time after a few minutes and it ran clean and did not break up. Certainly sounds like a wire or something wrong with the 02 after it warms up.

The GTO has two 02 pigtails. One going from the harness to where it attaches to the side of the transmission, and the other is the pigtail lead from the 02 which attaches to it. Both pigtails use standard 02 type plug ins. The 02 pigtail lead has been changed twice in 5 years, each time the 02 was changed. I have some time tomorrow, so I will check the grounds and the connection at the harness. Who knows without going under the car mavbe a wire is burned or frayed or corroded.

Does anyone know offhand, what the 02 voltage is from the signal wire when cold and also hot? Also, what should the voltage be to the heater circuit?

 

 

Good point. Keep in mind I am getting a left bank signal. I thought I would switch the 02s, but I will try your idea first. I am using ACs.

 

Another question. Are the downstream 02 sensors the same as the upstream. Are they interchangable?

 

 

I did a little research and the sensors are listed under two different part numbers. But, the difference is in the pigtail connector length. Many here said the rears would work. I have some time tomorrow and I'll post what I find out. BTW VandykeT/A maybe onto something. The motor is flooding and you can smell it. The false lean signal is making the ECM flood the motor. I'll switch sensors tomorrow. I'll take one from the rear first.

 

Burning oil? Putting additives in your gas? Coolant leaking into the combustion chamber? Is your o2 sensor placement stock?

o2 sensors normally last a long time.

 

Another thing to consider is fretting on the connector terminals. That might be giving you an intermittent issue where you will get a normal signal for a while, then it will drop to a low voltage.

 

I took VandykeTA's advice and disconnected the 02s today. The car ran rough for a few seconds and then went into open loop and ran clean. I thought it diagnosed the problem and thought the 02s were the source of the miss. But, after 10 minutes the car started to miss again. It missed so bad that it wouldn't idle, so i opened the hood and blocked open the TB little with a screw driver to get an idle.

After that, I remembered I had a Maf problem with the car a few years ago. That turned out to be the Maf plug in. So, I jiggled the left bank coil pack connector and voila the motor ran clean. So, I disconnected the plug in and cleaned the connection with brake cleaner and applied dielectric grease to the prongs and gasket. The connector snapped backed together and felt good. I took the car for a 20 minute drive and there was no missing and no codes.

When I returned, I did the right back too. When I restarted the motor, I heard the satisfying whistling sound of a smooth motor. The cleaning helped I'm sure, but the grease prevents any arcing or cross firing in the connection. Before I started, I remembered when cars used to have distributor caps. Crazy misfires would occur and examining the cap would show arcing between terminals. Sometimes the arc lines were easy to track, looking like little ant trails going from one terminal to the next. Sometimes arcing would occur but you could not see the trails with the eye.

The solution would be to replace the cap of course, but if the trails were not visible I would but a thin film of grease on the inside of the cap to see if it would help. Now as then, the grease is probably stopping connector arcing. I always used grease on the plugs and wires when I changed the plugs. In the future, I will also grease the coil connectors whenever I change the plugs. Tomorrow the car gets the acid test. I will take out for 30 miles or so and post the results.

 

We are on the same page with this one if you meant the coil connectors. Before I read your post I did the above connection cleaning and greasing. But, thanks for the suggestion. It turned the trick.

 

PS: the rear 02s on this car (04 GTO) are not interchangeable with the fronts. Although the sensor itself maybe the same, and although the pigtails are the same length, the connectors are different.

 

it's always weird when a MAF problem causes an issue with a single bank. it always throws me off, because you expect it to effect both banks. that's not always the case, though.

FWIW, dielectric grease also supposedly helps combat fretting to some degree, although in my experience just replacing the connector is the best solution.

 

UPDATE: After cleaning the left bank coil pack connector. The problem went away. I guess when the power is lost to the left bank, the cylinders misfire or do not fire at all and set a lean condition code. The ECM believes it is lean because no burnt gases pass by it.. Instead, unburned gases with oxygen pass by, and because of the amount of oxygen in the exhaust, the ECM interpretes the mixture is lean and starts to flood the motor.

I do not know if the plug for the coil pack harness is bad or if it is the body loom plug in. I changed the right bank harness a few years ago after a similar problem. All the wires look OK with no fraying. The pins are probably corroded or there was arcing or a slight crack not visible to the eye in the plastic of the connector. Does anyone know where I can get a new connector?? I know I can go to the junkyard and clip one out, but I would like to find a new one.

 

I would think any GM dealer would have that, though you might have to order it.

 

don't see the female harness connector, but whatever. i'm sure it exists somewhere. might want to contact caspers electronics.

https://www.rockauto.com/en/moreinfo...423044&jsn=426

https://www.rockauto.com/en/moreinfo...423044&jsn=422

 

The AC part number is: 12582190 and that is for the female plug in and leads from the connector to the coil pack. The male plug is attached directly to the body harness. So, the male connector would have to be spliced onto the loom. That part is hard to find. I will contact Caspers. I'm sure they know something about it. Thanks for the suggestions, especially the tip from VandykeTA. When I ran the motor for 10 minutes with the 02s unplugged before it started to miss, I knew it was not an 02 problem. That's when I decided to check the plug ins.

Let this stand as a lesson to all before you start throwing parts onto the car. False 02 readings are caused by many different things. I follow the old adages: (1) if its not broken, do not fix it; and (2) do not throw parts at the car, because you still have to find the real problem anyway.

BTW, the car ran good today. The weather is getting colder and with that and a good coil pack connection she ran strong.