Multiple codes P141, P1135, P1155, P0300, 301 & 302 -

Tiny
LARRYNEW
  • MEMBER
  • 2001 LEXUS RX 300
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 156,000 MILES
Check engine light is on, poor gas mileage, engine light begins to flash when exceeding 50 mph. Otherwise runs well. WHERE DO I START. At this point about ready to figure out how to get rid of the car. Ugh. From reading the lexus forum, 141 is an oxygen sensor. Which one? If I replace that first, will it clear the others?
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Monday, December 8th, 2014 AT 7:29 PM

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Tiny
CARADIODOC
  • EXPERT
P0141 - Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
P1135 - O2 Sensor Heater Circuit Low Voltage (Bank 1 Sensor 1)
P1155 - O2 Sensor Heater Circuit Intermittent (Bank 2 Sensor 2)
P0300 - Random/Multiple Cylinder Misfire Detected
P0301 - Cylinder 1 Misfire Detected
P0302 - Cylinder 2 Misfire Detected

Nope. Back up a minute. First of all, the flashing Check Engine light means too much raw fuel is going into the exhaust system where it will overheat and damage the expensive catalytic converter. You're supposed to stop the engine as soon as you can do so safely. The obvious place to start looking is all the misfire codes. A spark-related misfire will allow unburned fuel and oxygen into the exhaust where the oxygen will be detected as a lean condition. The Engine Computer will respond by commanding more fuel, hence the poor fuel mileage.

The fault code 141 only indicates the circuit that needs further diagnosis. Fault codes never say to replace parts or that one is bad. In this case, the sensor is after the catalytic converter and it only reports on the the converter's efficiency. It has nothing to do with fuel metering calculations.

While a sensor referenced in a fault code could indeed be the cause of it, you first have to rule out wiring and connector problems. Given the multiple codes here too, it is very much more likely you're going to find a major wiring issue. I would start by looking for a wiring harness that fell down onto hot exhaust parts and melted through until some wires touched together or to ground. Replacing one sensor isn't going to solve all he O2 sensor codes, and they won't solve the misfires. Those could be nothing more than worn spark plugs, wires, or ignition cols.
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Monday, December 8th, 2014 AT 7:51 PM
Tiny
LARRYNEW
  • MEMBER
Thanks, I will look to see what I can find, but wiring issues are very much over my head and I'm afraid a Lexus dealer shop is going to run me into the thousands to find and fix. Not a happy day.
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Monday, December 8th, 2014 AT 8:01 PM
Tiny
LARRYNEW
  • MEMBER
Would a bare wire on one of the oxygen sensors cause the issue? I have read in some of the forums that the wiring to back o2 sensor becomes loose and can become exposed for this model.
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Monday, December 8th, 2014 AT 8:04 PM
Tiny
CARADIODOC
  • EXPERT
The O2 sensor codes leave me with more questions than answers. Code 1135, low voltage, is caused by the heater wire being shorted to ground, but the heater wires for all the sensors used to be tied together into one common circuit. On a newer car such as yours, they are often split up into individual circuits so they can each be monitored individually. Codes 141 and 1155 as you can see, aren't very descriptive. You know which circuit to look at, but you don't even know what you're supposed to be looking for.

Typically all the wires for all the O2 sensors will be bundled into one harness that may travel down the center of the floor right under the carpet, or it might be under the floor. Find one of the rear sensors, then follow its wires into the harness and see where it goes. My suspicion, since code 1155 refers to a sensor in front of a catalytic converter, is that's the area the cause of all these codes is going to be found.

Also disconnect any connectors and look at the terminals in them. If you see corrosion between multiple pins, that can cause fault codes. Stretched terminals will cause codes too. Those are terminals that are spread open too far to make solid contact.
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Monday, December 8th, 2014 AT 8:19 PM
Tiny
LARRYNEW
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Thanks, have a good evening.
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Monday, December 8th, 2014 AT 8:28 PM

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