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2004 Ford Escape P0136

My check engine light came on in my 2004 Ford Escape XLT. Code showed p0136 as Bank 1 Sensor 2. Was replaced 1 year ago. Mechanic said sensor was good but manifold converters were heating to 400 degrees and I needed new converters. He said it could overheat and blow my headgasket? Is this true?Car has been very well maintained and only 2 coils replaced last year. Could this be converters and can I safely drive it? How do I know if it’s not coils or something else? It drives fine except fir the CEL. Thanks in advance. What’s a girl to do to get an honest answer.

Straight off the interwebs for a P0136 code

Common Problems That Trigger the P0136 Code

  • Defective oxygen sensor/air fuel ratio sensor
  • Defective oxygen sensor/air fuel ratio sensor heater circuit
  • Exhaust system leak
  • Intake air system leak (including vacuum leaks)
  • Low fuel pressure
  • Defective Engine Coolant Temperature Sensor
  • Defective sensor wiring and/or circuit problem
  • PCM software needs to be updated
  • Defective PCM

Do you see anywhere in that list “bad catalytic converter”? No, you don’t. Ask your mechanic why he thinks 400 degrees is too high for a manifold, let alone a converter. The average light off temperature at which the catalytic converter begins to function ranges from 400 to 600 degrees F. The normal operating temperature can range up to 1,200 to 1,600 degrees F. But as the amount of pollutants in the exhaust go up, so does the converter’s operating temperature.

The O2 sensor may have failed again or your mechanic may have buggered up the wires when he replaced it and now you are seeing the result. You need to find a new mechanic, the one you have isn’t very good.

Thank you. If he got my “wires crossed” wouldn’t my engine light have come on sooner? It’s been 1 year and 1 month since the Bank 1 Sensor 2 was replaced. Auto Zone and O’Reilleys, both, confirmed the code. One mechanic( I have talked to several now)told me that my sensor was good, the converters were bad. One told me basically what you said and the other told me today what I had posted that if I didn’t change my converters soon that I could blow a gasket. (I feel like I am going to blow a gasket🙂) I think I will stick with Mechanic #2. With your background, I feel confident you know what you are talking about.

On a 04 Escape w/2L engine, P0136 is for a circuit malfunction for a downstream (after the cat) sensor. The computer monitors the voltage produced by the sensor continuously, and it should only be within a certain voltage range. The DTC is saying the computer is observing readings outside that range. The first thing I’d do – as a driveway diy’er – is put on o’scope on the output of that sensor and see what voltage range it is producing. No need to guess, the sensor is right there ready to be measured. The most common things that would cause an out of range problem like this are a wiring harness problem (pinched, shorts, etc) , exhaust leaks, and (least likely, contaminated/damaged/faulty sensor). Beyond measuring the output voltages, also ask the shop to look for anything dripping on the external part of the sensor, and ask if they or anyone might have ever used a sensor unfriendly sealant while working on the car. Concur w/MM above, unlikely to be a cat problem, especially if the only reason to think that is a 400 deg F cat measurement. The way a cat problem is normally diagnosed is by observing (usually using a scan tool) the simulataneous signals produce by the before-cat and after-cat o2 sensors. There is a known pattern these follow if the cat is good. If that pattern isn’t observed, the cat is diagnosed as faulty.

My guess is you either have a wiring harness problem or exhaust leak. Re the latter, when the engine is running w/an exhaust leak outside air will be pulled into the exhaust system during certain phases of the crankshaft cycle. That will confuse the computer to no end, b/c it assumes everything in the exhaust pipe is coming from inside the engine. If there any sign at all of an exhaust leak, repair that before presuming there’s any other problem.

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I know this is a long shot… I have a small oil leak coming from my timing chain cover. It’s been there for over 100,000 miles. I kept waiting for something else to go wrong because it was going to be so costly to fix. Could oil from the cover be dripping on the sensor? I really need a manual so I can see this stuff. I think I am going to get country girl crazy and figure this stuff out. Thank you for helping me.

If oil drips on the o2 sensor, yes, that can prevent it from working correctly. Most o2 sensors require a small opening from the inside of the sensor to the outside air in order to work. But it seem unlikely such an oil drip would come from the timing chain cover, as the o2 sensors are usually well removed from that part. In any event, oil on the external part of the sensor should be easy enough for the shop to see.

An inexpensive Chilton’s or Haynes manual would probably have the wiring diagram for the o2 sensor circuits. Maybe your local public library even has one you could borrow. While there ask if they have any other auto repair help, such as the All Data computer data base.

I called the muffler guy back this morning to confirm what he said on Saturday after telling me that my converters were bad. This is what he said, “ When I tested the temperature it was 350*, the temperature immediately went to 430* and I shut it off because it was getting too hot, too fast.”All three converters were bad and the last one under the car was crystallizing. I asked him if I needed to fix some other things first before I changed the converters and he said”No, I need to change those out first before I can determine what else is wrong” And not to drive it anymore than necessary because I can blow a head gasket or do major engine damage. My CEL just came on about a week ago. He’s shooting me a line, isn’t he? I’m going to take it somewhere that tells me what you guys said about the exhaust leak and harness. I appreciate you guys!:girl:t2:

Catalytic Converters bad because of a temp of 350?? Yeah he’s trying to to feed you a line bad…

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Suggest to Google “catalytic converter crystalizing”. I doubt you’ll find this is a common diagnosis as reported on the inter-webs, if it even is a diagnosis except perhaps for diesel engines. I don’t believe I’ve ever heard cat crystallization mentioned here before. Besides Googling you might type that into the forum search bar to; click the icon that looks like a magnifying glass upper right on this page. If I had those symptoms on my own vehicle and a visual inspection didn’t turn up anything, as I posted above, first off I’d ask my shop to use a lab o’scope to inspect the signal output from the suspect O2 sensor, and then use a scan tool to compare the before and after cat o2 signals. I think that would get to the bottom of this problem faster than replacing all 3 cats. Not saying you won’t wind up replacing some or all of the cats, but some common sense testing makes sense first, imho. Be aware that it is possible the shop has already done these things, and just doesn’t want to explain their process in this amount of detail to you for some reason.

Well, I finally found a mechanic after “interviewing” about 6 different ones and asking questions about what you guys posted. After a complete examination, only my 02 sensor was bad. Converters are all fine. Saved over $1000. Car is in great shape. I owe y’all a world of thanks!:blush:


Good to hear! Thanks for letting us know,

Excellent news!

I would suggest that you log onto Yelp and post this information, which indicates that the “muffler guy” is-at best–incompetent, and may well be an outright thief. Don’t you think that you owe it to other folks in your community to let them know about this guy’s business practices?

Very good point!

Good to hear you are back on the road and p0136-less … :slight_smile: … … good for you!