- Feb 14, 2004
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I honestly don't know what you're asking. ECM's never set DTC's 'because a part is broken.' They detect something that is considered a manfunction, which generally falls into one of two categories:
1) A circuit is broken. Basically, points A and B are not touching, even though they should be. This can be in regards to an input (sensor) or an output (usually a solenoid).
2) The ECM (or PCM or TCM) is receiving a signal from something, but it's not the signal that it wants or expects. This is pretty much all on the input side. This can be a signal that is totally out of range. Like, say, an ECT with a resistance that indicates the engine is currently running at 800* or something. Or it can be a good signal(s) that indicate a problem with another part. Like flagging misfires based on the input from the crank sensors, or setting an 'incorrect gear ratio' code based on the input and output shaft speeds of the trans.
Hopefully that kinda makes sense.
In this case, your code is for a low voltage from the rear O2. This could mean the ECM is seeing a voltage SLIGHTLY lower than it wants to see, which would likely be from a bad O2...or it could be seeing no voltage whatsoever. I can't remember if the circuit actually being open (failed continuity check) will generate a different code or not. P0136 is just 'low voltage.'
You should try and monitor the rear O2 voltage with your scan tool. Even though it will update really slowly, you'll be able to see if it's got any activity, or if it's just 'flat-lined' at 0v.
Either way, it's not indicative of a bad catalytic converter. I will correct myself and say that it COULD be an exhaust leak, though. Low voltage = lean = higher concentration of oxygen than it should be seeing. I had initially brainfarted and thought P0136 was indicating no continuity on the signal circuit instead of just low voltage.
But low voltage can also mean the O2 is just not able to generate a voltage in the proper range anymore.
No you got it, that's exactly what I was asking - whether that code was saying that the sensor itself was broken/malfunctioning, or that the thing the sensor was sensing was acting up (the oxygen). So it sounds like it could be a few things:
1. Bad sensor
2. Bad Cat
3. Exhaust leak
I have no experience working on cars, so all this stuff is very new to me and I appreciate the help! Got my Car Repair for Dummies book & my OBD-II scanner and I'm ready to rock & roll :biggrin:
