Question about 1996 Jeep Grand Cherokee

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Have had this engine code going on 6 weeks now. Have replaced the two rear O2 sensors but am still getting this code. When the weather is really hot (over 100) the engine light does not come on. I have replaced both sensors and disconnected the negative terminal for 30 min to try and reset the ECM.

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  • jumper780 Aug 19, 2010

    Sorry, the make is a 2008 Jeep Wrangler Sahara Unlimited 3.8L.
    The code is a P0158
    I only have 51K on the engine. My battery did go dead yesterday and I had it replaced. The engine light was off imediately after replacing but then went back on again the next day.

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Sorry but your post did not identify specifics like year/make/model of your Jeep PLUS engine size and trans type AND the actual codes like P0171

However, I am assuming your codes are for lack of 02 switching which basically means that you will need new CAT(s) depending on a few additional tests

Please update your post so I can answer your question to the best of my ability


Sean

Posted on Aug 19, 2010

  • Sean Reisdorf
    Sean Reisdorf Aug 19, 2010

    here are your possible concerns....
    short to power on the signal circuit
    short to power on the return circuit
    open circuit on the signal circuit
    open circuit on the return circuit
    defective O2
    Defective PCM

    sounds like you already took care of the last two so that only leaves circuit concern

    while I understand you already replaced the O2, there are still about 20 feet of wires that run from the new O2 back to the PCM

    trace these wires CLOSELY and look for signs of damage
    I have seen some melting issues near the manifold

    no open recalls or TSB's at this time


    Sean

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1 Answer

How do I find out Which Oxygen Sensor is Bad, Upstream or Down-Stream ?? I Pop 2 Error Codes. #1- Spark Plugs, #2 O2 Sensor(s) [doesn't designate which one as my Car has 2]


with out the codes cant tell which o2 sensor is causing the issue , before you change any sensors i'd recommend using a fuel addative , get one that cover the catalytic convertor as well as fuel and engine parts , give it a long run at a good speed to get the engine to a high operating temperature as most o2 sensor issues are because the tip is coated in carbon etc and cant detect the exhaust gases, another thing to check before replacing o2 sensors is the air intake pipe work as a split , tear etc in the air intake side will give a false reading on the exhaust side as the intake readings are affected by the split , hope this helps

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There is a chance that your temp sensor is the culprit on both codes. The temperature sensor is what tells the ECU how hot or cool the engine is and weather or not to keep the engine in phase lock loop, or choke, mode. If the engine stays in phase lock it will run too rich and the O2 sensor will not be able to compensate.

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2005SANTA FE FUELING PROBLEMS


You may need a shop to take a look at it. The code for the cat means the computer does not like the readings coming from the O2 sensors. The cat may be working correctly, or you may have a fuel problem. Or one of the O2 sensors may be faulty.
Fuel pressure and venting problems in the gas tank can cause other problems.

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What could cause my bank 1 O2 sensor to keep going bad


For the code pulled was diagnostic trouble code diagnostics done or was the O2 sensor just replaced > What was the code # P0xxx what . There are a number of codes for the O2 sensors on cars . They don't say replace the O2 sensor . diagnostics must be done , electrical circuit testing , plus other tests

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is that the code you get from comp is PO420 eng light if so worst news either you have an exh leak between o2 sensor 1 and o2 sensor 2 or the front o2 sensor is lazy or the front catyletic converter is not working

basicaly code is only triggerd when engine is hot and the front o2 sensor and the rear o2 sensor read the same voltage when conv is working the front o2 sensor will fluctuate rapidly from 0v to 1v and rear o2 sensor will remain steady at 0.5v

try to explain best i can plz vote comment or reply if you need more help

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I just get a 2000 lanos but the check engine ligth is ON when i put it the code reader says to me 2 codes : 1st code is P0137 and p1336 say a lot lf items but got to be only one of those , whath can be???...


Essentially the same as P0136, P0137 refers to the second oxygen sensor on Bank 1. P0137 means the O2 oxygen sensor's voltage remained low for longer than 2 minutes. This, is interpreted by the ECM as a low voltage condition and sets the MIL. Bank 1 Sensor 2 is located to the rear of the catalytic converter and should produce an output signal relative to oxygen storage capacity of the catalytic converter. This rear (sensor 2) sensor is less active than the signal produced by the front sensor. However, if the ECM senses the sensor is inactive, this code will set.

Symptoms There may be no visible symptoms to the driver, other than the MIL (Check Engine / Service Engine Soon) illumination.

Causes
A code P0137 may mean that one or more of the following has happened:
  • Faulty O2 sensor Exhaust leak near the rear sensor
  • Plugged catalyst
  • Short to voltage on O2 signal circuit
  • High resistance or open on O2 signal circuit

  • Possible Solutions
  • Replace faulty sensor
  • Repair exhaust leak near the rear sensor
  • Check for restriction in catalyst and replace as necessary
  • Repair short, open, or high resistance on o2 signal circuit
The other code is your crankshaft position sensor. You need to replace both of the sensors and the check engine light will go off.

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My 89 Toyota pickup idles too fast in cold weather


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Check engine light was on. OBD II scan said both pre-Cat 02 sensors running lean. Also shows P0000 code which is a undefined code. S dash light comes every few days then transmission will stay stuck in 4th...


The pre cat sensors running lean does not mean they need to be replaced. They are are detecting a symptom. You need to know why.

If you are using a basic scantool (code only) you need to look up the P0000 code.
I thought this an odd code. I looked it up in my Autotap unit and it does not exist. The lowest # P (powertrain) code I have listed is P0016.

A regular scan tool, won't scan transmission or body codes, mu Auto tap doesn't either. You need a Tech 2 from the dealer for transmission codes.

First some history. The first O2 sensor was introduced in 1976 on a Volvo. California vehicles got them next in 1980, then federal emission laws made O2 sensors virtually mandatory on all cars and light trucks built since 1981. And now that OBD-II regulations are here (1996 and newer vehicles), most vehicles now have multiple O2 sensors, some as many as four!
The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust. The signal from the O2 sensor tells the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen).
A lot of factors affect the richness or leanness of the fuel mixture, including air temperature, engine coolant temperature, barometric pressure, throttle position, air flow and engine load. Other sensors monitor these factors too, but the O2 sensor is the master monitor for what's happening with the fuel mixture. Problems with the O2 sensor can throw the whole system out of whack.
The computer uses the oxygen sensor's input to fine tune the fuel mixture for the best balance of power, economy and emissions. The engineering term for this type of operation is "closed loop" because the computer is using the O2 sensor's input to adjust the fuel mixture. The result is a constant flip-flop back and forth from rich to lean which helps the catalytic converter operate at its best and keeps the average fuel mixture in proper balance to minimize emissions. It's a complicated setup but it works.
If no signal is received from the O2 sensor, like when a cold engine is first started (more on that in a minute) or the 02 sensor fails, the computer orders a steady, rich fuel mixture. This is referred to as "open loop" operation because no input is used from the O2 sensor to fine tune the fuel mixture. If the engine fails to go into closed loop when the O2 sensor reaches operating temperature, or drops out of closed loop because the O2 sensor's signal is lost, the engine will run too rich causing an increase in fuel consumption and emissions. As you might have guessed, that will set a code and turn on your check engine light.
How does it work? The O2 sensor produces a voltage once it gets hot. The sensor compares how much oxygen is in the exhaust to the oxygen in outside air. The greater the difference, the higher the voltage reading.
If you ever replace an O2 sensor (and if you're a DIY'er this is something you will do eventually), its important to remember that the O2 sensor needs to "breath" outside air to work. So don't put any grease on the sensor because it could block this air flow.
An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen left in the exhaust. When the mixture is lean, the sensor's output voltage will drop down to about 0.1 volts. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around 0.45 volts.
When the computer reads a rich signal from the O2 sensor it leans the fuel mixture to reduce the sensor's reading. When the O2 sensor reading goes lean the computer reverses again making the fuel mixture go rich. This constant flip-flopping back and forth of the fuel mixture occurs anywhere from 2 to 7 times a second at 2500 rpm on OBDII vehicles, depending on what type of fuel injection system they have.
The oxygen sensor must be hot (about 600 degrees or higher) before it will start to generate a voltage signal. Many oxygen sensors have a small heating element inside to help them reach operating temperature more quickly.
Ok – that was a lot of info on what they do and how they work. The next thing to know is that trouble codes relating to O2 sensors are very common. But you really need investigate further before replacing an O2 sensor just because you got that trouble code. Armed with the information above on how often the O2 sensor "flips" back and forth and AutoTap or another scantool that allows you to monitor O2 sensor voltage, you can be certain whether the O2 sensor itself is really the problem. These sensors can be pricey, so don't just replace them the first time you see that trouble code!

The O2 sensors are expensive, diagnose what really is going on.

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