Question about 2003 Mercury Sable
DTC P1031 - HO2S Heater Current Monitor Control Circuit
Its refer to the Oxigen Sensor; the most common issues for lean codes are:
1. Vacuum leaks - check for failed or loose vacuum lines, leaking intake gaskets, intake air tubes loose or any other source of un-metered air leaks (leaks after the Mass Air Flow Sensor)
2. Restricted fuel filter or bent/pinched fuel system lines
3. Incorrect input from other sensors, such as the Mass Air Flow Sensor, which may not always drop a separate code
4. Engine misfire – Yes I know this one may seem weird. You might think that if there is a misfire then you will have all that unburned fuel and it should read rich; right? Well the O2 sensors read only oxygen content in the exhaust, so if you have all that unburned fuel from incomplete combustion then, you guessed it, you also have all that unburned oxygen. High O2 content in exhaust equals a lean reading! There are also some other possibilities such as an internally leaking EGR system, (but this will typically set a separate code). A leak in the exhaust system before the O2 sensor will also cause incorrect readings. And always check for after- market modifications. These can throw a wrench into the works! The only other possibilities (however unlikely), are wiring issues, computer concerns or a bad O2 sensor! There now that I’ve said it, on to rich codes.
The possible causes of rich codes are:
1. A leaking or faulty fuel injector
2. Fuel injector driver in computer shorted, or wiring short for injectors (likely a ground short)
3. Leaking or faulty fuel pressure regulator or restricted return line
4. Faulty evaporative emissions system - bleeding fuel vapors into engine (not commanded by computer)
5. On newer models a faulty fuel pump or fuel pump driver module
6. Faulty readings from other sensors such as a Mass Air Flow Sensor. You may actually be getting more air than the MAF tells the computer
7. Exhaust leaks before the sensor will cause erratic readings
8. After market components or performance chips
9. And yes, if I dare say it, possibly a computer, wiring issue or even a faulty O2 sensor!
The other codes we should address are those related to the sensors located after the catalytic converter. Though these may appear identical to the oxygen sensors pre-converter, they perform an entirely different task and are known as Monitors. The only job of these sensors is to “monitor” the efficiency of the catalytic converters. The readings from these sensors should be much more stable and not fluctuating like the front O2 sensors. The computer compares the readings from the oxygen sensors (pre cats) and the monitors (post cat) to determine if the catalytic converters are doing their job and “cleaning” the exhaust. You never want to replace a monitor for a rich/lean concern as they have no bearing on these codes. As the converters begin to fail, you will see the monitors voltage readings follow the oxygen sensor readings. Technically these are all “oxygen sensors” but it is important to distinguish the difference between pre-converter & post converter sensors, so I find it easiest to stick to calling the back ones monitors.
Hope helps (remember rated this).
Posted on Jul 14, 2010
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Posted on Jan 02, 2017
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