4 error codes all at once?

GoneYukon · March 17, 2006

I was towing a heavy load (7000#) in tow/haul mode on a 400 mile trip. The truck was cruising in 3rd, and on the hills would shift into 2nd. It did great until it got into really hilly terrain (FL hills). On one of the asents the SES came on. The tranny started to feel like it was slipping in 2nd a bit and I figured they were related. I babied the truck the remainder of the way. Once I took the load off the truck and let her cool down the tranny went back to normal shifting, however the SES light is still on. I took it to AutoZone and got:

P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)

P0137 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)

P0151 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)

P0157 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

Is is possible for all 4 O2S to go bad all at once? Can I clear the MIL and see if it comes back on? The truck is driving fine and shifts fine. The tranny fluid is not burned. I'm dropping the pan this weekend to examine the sediment, but any ideas what's up w/ the MIL?

ZZebes · March 17, 2006

Fuses???

sjspor · March 17, 2006

That almost sounds like a slug of kitty crap ola gasoline, the low voltage would be the output of the sensor, below is generic how they work....

An Oxygen sensor is a chemical generator. It is constantly making a comparison between the Oxygen inside the exhaust manifold and air outside the engine. If this comparison shows little or no Oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between 0 and 1.1 volts. All spark combustion engines need the proper air fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to one part of fuel. When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gasses leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts. The sensor does not begin to generate it's full output until it reaches about 600 degrees F. Prior to this time the sensor is not conductive. It is as if the circuit between the sensor and computer is not complete. The mid point is about 0.45 volts. This is neither rich nor lean. A fully warm O2 sensor *will not spend any time at 0.45 volts*. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an "illegal" value, it judges the sensor to not be ready. It remains in open loop operation, and uses all sensors except the O2 to determine fuel delivery. Any time an engine is operated in open loop, it runs somewhat rich and makes more exhaust emissions. This translates into lost power, poor fuel economy and air pollution. The O2 sensor is constantly in a state of transition between high and low voltage. Manfucturers call this crossing of the 0.45 volt mark O2 cross counts. The higher the number of O2 cross counts, the better the sensor and other parts of the computer control system are working. It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil, sound insulation, undercoating or antifreeze, (among other things), this comparison is not possible.

GoneYukon · March 17, 2006

That almost sounds like a slug of kitty crap ola gasoline, the low voltage would be the output of the sensor, below is generic how they work....

Thanks for the explaination of the O2S. I suppose it could be bad gas. As I recall it did happen after I filled up. I put 93 octane (Chevron) in it when I filled up to reduce any chance of pinging. Normally, I put 87 in it.

The problem with that theory is that I then drove the truck the same 400 mile trip back home the next morning. Although I didn't run the tank dry with what could've been the bad gas, I just filled it when i had the chance. After the potential bad gas fill-up it never got below 1/2 tank until I topped it off. So the bad gas would've been diluted with the succeeding fill-ups. Hmm...

How can I clear the MIL? I pulled the neg off the battery for a few mins but its still there.

Fuses???

I don't think so. Everything works.

sjspor · March 19, 2006

If indeed what ever caused all 4 codes was a one time passing fluke, the mil will turn off on its own and a set number of clean driving cycles, or use a scan tool and clear the codes, turn the lamp off.

GoneYukon · March 20, 2006

If indeed what ever caused all 4 codes was a one time passing fluke, the mil will turn off on its own and a set number of clean driving cycles, or use a scan tool and clear the codes, turn the lamp off.

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Thanks, I'll give it a shot. I have to believe that 4 O2S reporting low voltage all at the same time was due in part to the load I was towing and the inclines I was towing it on.