I have a 2003 caddy cts. Engine light on and codes say o2 sensors, replaced all and engine light still on reporting a bad sensor. Have chased it for a year. Now they say it could be a bad PCM . Is the

These may be few possible reasons why the check engine light won't go away after replacing the O2 sensor in your 2000 Mitsubishi Eclipse V6

·The wrong O2 sensor was replaced or the O2 sensor is properly connected to the wiring harness(any signs of damage or corrosion).
·Sometimes, issues with the engine, such as misfires, vacuum leaks, or problems with the fuel system, can trigger the O2 sensor to report a problem. Ensure your engine is running smoothly and there are no other issues that could affect air/fuel ratios.
·The new O2 sensor is defective. If the O2 sensor is working properly, then the check engine light could be due to another problem with the exhaust system, such as a leak or a problem with the catalytic converter.
·Problem with the wiring to the O2 sensor. If the wiring to the O2 sensor is damaged or corroded, it can cause the sensor to malfunction and trigger the check engine light. To diagnose the exact cause of the problem, you will need to have the car scanned by a qualified mechanic. The mechanic will be able to read the trouble codes from the computer and use that information to pinpoint the problem.

If the sensors were replaced an DTC'S come back has to be a wiring problem or PCM ,
The ECM detects that the HO2S heater low control circuit voltage is between 2.6-4.6 volts when the heater is commanded OFF, indicating an open HO2S heater circuit.
Is the fuse open?
All four codes refer to the heating element circuit ! there is a relay in the under hood fuse box that supplies B+ voltage to the O2 sensor heating elements . I would change that or test the relay , videos on you tube on testing relays .
MAIN Relay
--
LO SPEED Relay, HI SPEED Relay, S/P FAN Relay, PRE O2 Fuse, IGN-1 Fuse, ECM Fuse, POST O2 Fuse, and INJ Fuse
Also check
POST O2 Fuse
10 A
HO2S Bank 1 Sensor 2 and HO2S Bank 2 Sensor 2
PRE O2 Fuse
10 A
Heated Oxygen Sensor (HO2S) Bank 1 Sensor 1 and HO2S Bank 2 Sensor 1

The P0140 code is caused by or is affected by the P0141 code. Fix the P0141 code first before worring about the P0140.
It is good you had the connections cleaned as oil contamination will cause a problem with the O2 system.
The "automotive electrician" should have performed a continuity test from the O2 sensor heater fuse to the PCM connector were the heater is grounded. The resistance value should be 35ohms. If the value is too high, the PCM will set the P0141 code. I would suspect you have an open circuit in either high or low side of the O2 sensor heater circuit.
Good luck.

You do realize you have 4 o2 sensors on the vehicle? Obtaining a reading from its computer (failure code) will not tell you exactly which sensor is faulty. In fact, no device currently that I know of will give you an error code to exactly which o2 sensor is at fault. You may have replaced a good sensor with a new sensor and hopefully you didn't throw the old sensor out. I would put the old sensor back in and start performing the process of elimination method with the known, new sensor. Currently, you are 25% there (2 banks, 2 o2's per bank).

If your O2 sensors are malfunctioning, the main symptom would be that the Check Engine light will come on. On some vehicles, an O2 sensor circuit shorted to ground can cause a no-start problem.
If the "Check Engine" or "Service Engine Soon" light is on and there is a code for the O2 sensors, I would like to also advise you that many O2 sensor codes are not caused by the O2 sensors themselves. In many cases, the O2 sensors are only REPORTING the problem. for example, a code P0171 "Oxygen Sensor Lean" code is rarely ever caused by the O2 sensor. It is usually caused by a vacuum leak or a failed Mass Airflow sensor (MAF) or Manifold Absolute Pressure sensor (MAP) or a bad fuel injector. In these cases, repairing the real reason that the engine is running lean will fix the O2 Sensor code without replacing the O2 sensor.

O2 Sensor codes rarely mean that the O2 Sensors are defective. Most of the time, the O2 sensors are reporting a problem that is occuring somewhere else in the system. If your are getting a code that says "O2 sensor lean" that means that someting on that side of the engine is causing that side to be running lean. This is usually caused by a vacuum leak, but may also be caused by bad injectors or low fuel pressure. If BOTH sides are reporting lean O2 Sensor codes at the same time, it is something wrong that affects both sides of the engine including vacuum leaks in the main hoses tied into the intake manifold including the PCV hose and the Brake Booster Vacuum hose or the brake booster itself, or the Mass Airflow Sensor. Defective Engine Coolant Temperature sensors can also cause these codes. If the code you are getting is a "O2 Sensor Rich" code, it is caused by something that is making the engine run rich. This could be a sticking injector, a failed Fuel Pressure Regulator, or an O2 Sensor circuit that is shorted to voltage, or a malfunctioning Mass Airflow Sensor.
If you want to save a lot of money and frustration, learn this: Fault codes NEVER tell you what parts to replace. Fault codes only tell you which of the many systems monitored by the computer are operating outside their expected ranges or "Window of Operation". It is up to the person diagnosing the vehicle to test the system that is reporting the malfunction and determine the cause of the failure and repair as necessary.

There are several types of O2 Sensor codes. There can be "Lean O2 Sensor" codes, "Rich O2 Sensor" codes, "O2 Sensor Slow Response" codes, or "O2sensor Heater Circuit" codes. The specific code that is being set changes the way you must go about diagnosing and repairing the problem. I will say however, that in about 80% of all the O2 Sensor code problems that I have had to diagnose, the O2 Sensor itself was NOT the problem. The O2 Sensor was only reporting a problem that was actually caused elsewhere. O2 Sensors are the final checkpoint in the engine management system. I think of them like a report card. If the O2 Sensors are right, the rest of the engine management system is right. If the O2 Sensors are not right, the rest of the engine management system is probably not right. (Except in the 20% of the cases where the problem is actually being caused by a failed O2 Sensor)

You'll need to give us the specific code, in the format P0xxx. Just saying "O2 sensor" doesn't mean anything. It could be the heater circuit, fuse, o2 sensor itself, etc. Changing an O2 sensor isn't too hard but you may not need to replace it/them.

Please report back with the code or look it up at http://www.check-engine-light.com

something keeps blowing the O2 sensor out...may be bad plug wires...the engine gettign too much gas...too little gas you would have to bring to a good mechanic not dealership

Bank 2 Sensor 1 is on the driver side - follow the right side of the engine down the headers which attaches to the catalytic converter. The o2 Sensor you're asking about (Bank 2 Sensor 1) is before the Catalytic. The o2 Sensor after the Catalytic is Bank 2 Sensor 2. Bank 1 Sensor 1 is on the passenger side as well as Bank 1 Sensor 2.