Hey guys, some of you may remember that I posted on my CEL that will not go away. I have a 4-1 HVE ceramic coated header, carsound cat (made for a Stang, small for a cat) and KRD exhaust. I had the O2 sensor relocated right after teh area where the collectors merge. I disconnected the negative on the battery and left like that for an hour. I then reconnected it, drove it home, left for a while and restarted it. After driving for a couple of miles, the CEL comes on again!!! I then stopped and disconnected the ECU fuse for a few minutes, and it came on again after a while!! I went to Autozone and the same codes are coming on again..P0131 and P0134..ANY theories or suggestions would be greatly appreciated..I'm sooo frustrated with this. BTW, I replaced both O2 sensors recently so that's not the problem.

I have to ask.. you have both sensors hooked up? One before and one after the cat? If that is the case, the only things I can think of are these.

1: bad cat.

2: Damaged wiring to the o2 sensors

3: Damaged o2 sensors

4: first o2 sensor is too far away from the exhast ports

The cat and sensors were bought around the same time new, which was two to three months ago. The first 02 sensor was orginally placed around 8 to 12 inches away (guessing) from the head and has been placed further down but was able to use O2 sensor without elongating the wires. The codes indicate that it's a problem with the first O2 sensor..something to do with the heater element.

DTC - P0131 (OXYGEN SENSOR CIRCUIT LOW VOLTAGE)

PRIMARY SENSOR: Front Oxygen Sensor


SECONDARY SENSOR(S): None


SYSTEM(S): Bosch


NORMAL PARAMETERS: Sensor output using scan tool with engine at normal operating temperature:

200 millivolts or less when decelerating suddenly from 4000 RPM

600-1000 millivolts when engine is suddenly raced.


Sensor heater resistance: 3-5 ohms at 194°F (90°C) ECT

CIRCUIT DESCRIPTION

The Engine Control Module (ECM) uses oxygen sensor signals to maintain the air fuel mixture at the ratio resulting in optimum fuel economy and reduced emissions. The oxygen sensor measures the amount of oxygen in the exhaust gases. The oxygen sensor is coated with a catalyst metal that causes the sensor to produce a voltage in the millivolt (mV) range whenever the sensor reaches a temperature of at least 600°F (315°C) and it is exposed to oxygen. The amount of oxygen in the exhaust gases indicates, to the front oxygen sensor, whether the air fuel mixture being supplied to the engine cylinders is rich or lean. The readings of the rear oxygen sensor are used to indicate the efficiency of the catalytic converter. The ECM calculates catalytic converter efficiency by comparing the rear oxygen sensor signal to the front oxygen sensor signal.


A normal oxygen sensor signal will constantly fluctuate above and below 500 mV, with the front oxygen sensor signal frequency of at least 5Hz (one crossing from above 500Mv to below 500Mv or below 500Mv to above 500Mv every 100ms) at 2500 RPM. Due to the effect of the catalytic converter, the rear oxygen sensor signal frequency will be lower than the front oxygen sensor signal frequency. When the front oxygen sensor output signal is above 500 mV, the air fuel mixture is considered to be rich; if the signal falls below 500 mV, the mixture is considered to be lean. If the rear oxygen sensor signal coincides with the front oxygen sensor signal a large percentage of the time, this indicates a loss in efficiency of the catalytic converter or a malfunction within the fuel system.


An oxygen sensor is inaccurate when the temperature falls below 600°F (315°C). The oxygen sensor uses a heating element to shorten sensor warm up time (open loop operation) and help keep sensor temperature above 600°F (315°C).

FAILURE CONDITIONS
After the Front Oxygen Sensor Heater is on for 3 minutes and 20 seconds, the ECM continuously measures the front oxygen sensor's output in 0.5 second intervals. If during two back-to-back trips the front oxygen sensor's output falls below -128 millivolts for 0.5 seconds, the ECM will set a code and the Malfunction Indicator Lamp (MIL) will turn on. This code indicates an unusually lean fuel air mixture being read by the front oxygen sensor or ECM.

Translation... You've got an air leak, or you're running damn lean.


P0134 Oxygen Sensor Circuit Inactive (Bank1, Sensor2)
DESCRIPTION
Obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three way catalytic converter is used, but for the most efficient use of the three-way catalytic inverter, the air ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio. The oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air-fuel ratio. This characteristic is used to detect the oxygen concentration in the exhaust gas and provide feedback to the computer for control of the air-fuel ratio. When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen sensor informs the ECM of the LEAN condition (small electromotive force: 0V)


When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio the oxygen concentration in the exhaust has is reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive force: 1V). The ECM judges by the electromotive force from the oxygen sensor whether the air-fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor causes output of abnormal electromotive force, the ECM is unable to perform accurate air-fuel ratio control. The heated oxygen sensors include a heater which heats the Zirconia element. The heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is low) current flows to the heater to heat the sensor for accurate oxygen concentration detection.

DTC detection condition
Background

When the heated oxygen sensor begins to deteriorate, the oxygen sensor signal response becomes poor.

The engine control module forcibly varies the air/fuel mixture to make it leaner and richer, and check the response speed of the heated oxygen sensor. In addition, the engine control module also checks for an open circuit in the heated oxygen sensor output line.

Check area
Coolant temperature sensor: Normal.
Heated oxygen sensor signal voltage has continued to be 0.1V or lower for 3 min. or more after the starting sequence was completed.

Engine coolant temperature is higher than 80°C (176°F).
Engine speed is higher than 1,200 r/min.
Engine load is 25% or more.


Judgment Criteria
Input voltage supplied to the engine control module interface circuit is 4.5V or more when 5V is applied to the heated oxygen sensor output line via a resistor.

Check area
Coolant temperature sensor: Normal.
Engine coolant temperature sensor is 50°C (122°F) or more.
Engine speed is between 1,500 and 3,000 r/min < M/T > or 1,100 and 3,000 r/min < A/T >.
Engine load is 25 - 60%.
Intake air temperature is -10°C (14°F) or more.
Under the closed loop air-fuel control.
Monitoring Time: 8 sec

Judgment Criteria
When the air-fuel ratio is forcibly changed (lean to rich and rich to lean), the heated oxygen sensor signal doesn't provide response within 1.28 sec.
Monitored only once per trip.

Probable cause
Heated oxygen sensor deteriorated
Open circuit in heated oxygen sensor output line
Engine control module failed




Both have something to do with running lean, or the o2 sensor running so cold, that it reads lean (even if you're not).
I would check the O2 sensor wiring for the proper 5V feed for the heating element. If you're not getting 5V then you'll have to go back and check the wiring to figure out where the fault is.

If you DO have 5V, then the problem is it's reading lean. You need to figure out WHY it's reading lean.

^^ If that doesn't help you, I don't know what will.

Thanks Random, that is about the best description I have ever seen.

Thanks for the help guys and especially to you Random for taking the time to write up that nice piece of information. Just out of curiosity, would installing my SAFCII help at all with this problem?

No, the problem is either with you running lean, or your front 02 sensor that's not heating.

lmfao...webtech is a very useful tool guys.

code 0134 indicates an inactive o2 sensor, so im going to guess you have a short in the wiring.

the safc might help, but it would be for the wrong reasons. i doubt there is actually anything wrong with the A/F mixture, just something wrong with the o2 sensor reading. if the o2 sensor is showing signs of being lean(when it is actually just fine) and you try to correct it with the safc, you will just be running super rich.

Thanks again for all your help but I made a mistake with one of the codes, it's P0131 and P0135 (not P0134) which indicates that there is a heater circuit amlfunction on the precat O2 sensor