Is It Me?

[crokett]

or the car?

Check engine light has been on more than off the last few weeks. Throwing the code for O2 sensors but the dealer says the cat converter is bad, not the O2 sensors. The cat is a warranty repair, the O2 sensors are not.

So in 77k miles on the Vibe I've had 2 O2 sensors, a cat and a fuel pump fail. Wondering what else will go sproing.

[BobSch]

Wondering what else will go sproing.

What's the most expensive piece that's not covered by your warranty?

[crokett]

What's the most expensive piece that's not covered by your warranty?

Engine. Or tranny. Mayhap I should look at timing belt/chain replacement?

[charliex]

2000 Neon with 56K. Bad fuel pressure regulator (pressure way too high) plugged the cat converter. The cat is a safety issue, so it was covered. To have the fuel regulator replaced was $117. I noticed that my MPG had dropped to < 30 and the check engine light was on again off again for several weeks before I questioned it.

[jking]

If the catalytic converter is covered under the warranty & you're being told it's bad I would get it changed. You don't want to have to pay that out of pocket.

[crokett]

If the catalytic converter is covered under the warranty & you're being told it's bad I would get it changed. You don't want to have to pay that out of pocket.

It is gonna get changed next week. They had to order the part today.

[cabinetman]

Can't you get a legitimate diagnosis of what's wrong? Maybe go to a qualified private shop that's not influenced by the warranty, and pay for a diagnosis.
.

[dbhost]

'04 F150 4x4. 59K miles tranny bit the big one the SAME DAY that the drivers side window regulator failed, in the down position, in winter...

That was New Years night for me last year...

I have the 100K extended warranty. It very much paid for itself...

I wonder if I can get the warranty to cover where the blackberry bushes on the hunting lease scratched the paint?

[crokett]

Can't you get a legitimate diagnosis of what's wrong? Maybe go to a qualified private shop that's not influenced by the warranty, and pay for a diagnosis.
.

My mechanic pulled the codes a few weeks ago and said it was throwing O2 sensor code. Then he said it could be the sensor, the cat or the computer and I should take it to the dealer cause the cat and computer are covered.

[cgallery]

But, why would you be going through a 2nd cat? Wouldn't that indicate improper combustion? Perhaps the 02 was at play?

[crokett]

But, why would you be going through a 2nd cat? Wouldn't that indicate improper combustion? Perhaps the 02 was at play?

Not a 2nd cat. This is first replacement on the cat. O2 sensors have already been replaced once (under the extended warranty I bought - just about broke even). The cat and computer are covered under some special federally mandated 80k mile warranty. The CEL came on before Christmas. My mechanic said the code was O2 sensors. He also said that could be the sensors, the cat or the computer. the sesors have nothing to do with combustion per se. The sensors sit fore and aft of the cat. They compare readings on the exhaust before and after it goes through the cat. If there is a discrepancy, then the CEL comes on. My mechanic said he could replace parts but he'd be guessing. He said let the dealer figure it out and then I could bring it back if I needed to.

[cork58]

O2 sensors and cats don't fail without a problem upstream. The O2 just relays the information to the ECM to let it decide what to do with fuel and ignition. That being said it is not that simple either. The system is very complicated and will only be solved by paying for scan while the service engine soon light is on. Codes only direct you to an area. After that area has been inspected and resolved then other areas will be tested. If the tech can condemn a part then the fix should be done at that point. We already know the O2 and cat are bad. The question is, WHY. The O2 just gives the information and the cat only burns the unused fuel. To much fuel will take out a cat very fast.

Just my thoughts

[mpc]

1996-later cars have to have "OBD-II" (On-Board Diagnostics, version 2), and pre-96 models that are OBD-II compliant, will have 2 "wideband" oxygen sensors per exhaust manifold on the engine: one on the cat converter inlet, one on the outlet. O2 sensors come in several styles/flavors:

1: original one-wire sensors found on the "feedback" carbureted engines of the mid-late 80s and the first generation elecronic fuel injected engines. These sensors output a voltage in the 0.2ish to 0.7ish range depending on the air:fuel ratio of the exhaust. If the exhaust is lean (excess O2, not enough fuel was present in the combustion chamber) the sensor will read a low voltage. If the air:fuel ratio is above the stochiometric point (14.7:1 air to fuel) the sensor will read something above 0.6 volts or so. It's mostly a RICH or LEAN "switch" function; but it won't tell you "how rich" or "how lean" - i.e. the sensor output barely changes when you go from slightly rich to waayy rich. Instead, it switches from 0.2ish to 0.7ish typically right at the 14.7:1 point. The engine control computer plays "high-low" watching the O2 output voltage... when the voltage is below 0.5 volts, the ECU thinks "okay, we're lean... richen up a tad and see what happens..." until the voltage suddenly jumps to above 0.5volts... then the ECU thinks "okay, now we're either really rich or a little rich.. but rich nonetheless... lower the fuel injector ON time a teeny bit to lean out the mix." It does this "hunting" operation constantly - usually 1 to 3 times per second - so the average air:fuel ratio is perfect. That gives the best (cleanest) emissions and makes the cat converter last the longest. These original style 1-wire O2 sensors took a few minutes to heat up - they need to be HOT to work right. So engine start-up emissions were typically lousy until the sensor started reading correctly and the ECU could start hunting.

2: To improve start-up emissions, O2 sensors started showing up as 3 or 4 wire types: the sensor itself plus 2 wires for an internal heater. The 4th wire was a dedicated ground wire, rather than relying on the bolts to the exhaust manifold for the ground. The heater made the sensor hot enough operate in just a few seconds. Such sensors though are still narrow band - they still only tell you "RICH" or "LEAN" but not how rich or how lean.

3: Wideband sensors: these sensors output a voltage or other signal that varies with the air:fuel ratio. You can determine the exact air:fuel ratio with such a sensor. They are far far more expensive that the narrow band style sensors, and they need some special control circuitry. Since the output signal varies with the air:fuel ratio, the engine computer doesn't have to "hunt" to get a good average... it can look at the output signal and know exactly what needs to be done to get a perfect 14.7:1 ratio. Almost all cars use wideband sensors now to get every last bit of clean emissions.

The O2 sensor between the engine and cat converter is used by the ECU to monitor the air:fuel ratios; the ECU then uses the sensor output to tune the fuel injector cycling to get the best possible emissions. OBD-II cars have an additional (expensive) oxygen sensor after the cat converter because the OBD-II regulations require the car to monitor the performance of all emissions systems parts - including the cat converter. For V6 or V8 engines with twin exhausts, generally you'll see a cat conveter on each side of the engine V, and 2 expensive wideband oxygen sensors per cat converter.

crokett's CEL code could mean either the cat converter is nearly worn out, or the O2 sensor after it is shot, or there is an exhaust leak allowing fresh air (fresh oxygen) into the exhaust flow near the cat converters. If the error code points to the first sensor, it means the engine itself isn't running well enough for the engine computer to get a 14.7:1 ratio: vacuum leaks, a fuel injector that leaks gas into the engine or is dirty and thus sprays too little gas, faulty ignition timing (rare these days with computer controlled timing), etc. Many of the wideband sensors will fry instantly if the engine is running (hot exhaust flow) and the sensor isn't "powered up" by the controller. So just a momentary flakiness of the wiring to the sensor is enough to blow that expensive part. Since the sensor is literally screwed into the hot exhaust pipes, you can bet the wiring is being cooked all the time...

mpc

[LinuxRandal]

The cat and computer are covered under some special federally mandated 80k mile warranty.

The federal Emissions warranty. I once had a electronic part fail, that they placed inside the distributor instead of elsewhere. I had a month and 1000 miles before it was out of warranty and they wanted to not have to pay for it.

Some of the things that could cause the sensor issues are also EGR valve going bad (exhaust gas recycling) or other fluids going through it (flooded area, or leaking antifreeze into your exhaust through manifold/head gasket leaks). As much as the check engine lights are nice (don't have to pull and clean your spark plugs once a year, put in new points, etc), they are only a general tool. There is still a lot of guesswork, without a factory manual and all the diagnostic tools (thousands of dollars and some are vehicle and year specific).

[crokett]

Lots of stuff
mpc

Thanks for the explanation. All I know is the dealer says the cat is bad.