O2 Sensor Question

michibronc

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Today's the first day I've driven the beast since I did about 3 weeks worth of body work. As luck would have it, a check engine light came on after about 30 miles of driving.

I stopped at autozone and they scanned. Two codes to report:

P0174 (Fuel system for bank 2 was too lean)

and

P0141 (Malfunction in heater circuit for oxygen sensor 2 in bank 1)

This has me confused. I'm supposed to be leaving for a wheeling trip right after work on Thurs. (tomorrow) and it looks like I need to change two oxygen sensors now! Can anyone shed some light on what needs to be changed? The truck is running great, but I don't want this problem to escalate into a cat converter failure nor do I want to deal with poor mileage for 400 miles this weekend!

Is it possible that this is a byproduct of not running for a few weeks? I also took it through a car wash to get all the dust off it today from the sanding and it had a under body blast feature. If it was a fluke, how many times must the truck be started to clear the code if it no longer exists?

 

BroncoJoe19

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Yesterday Miesk5 stated that he would be away for a week.

Perhaps this thread will be a little helpful.

http://broncozone.com/forums/index.php?s=&...ost&p=76967

Other than possibly gleaning some info out of it, be sure to check your conenctors to the O2 sensors... clean and tight.

Look for vacuum leaks, and exhaust leaks before the O2 sensors.

6-8 startups and warms ups should clear the CEL, but the code may stay in memory for 40-80 startups.

 
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michibronc

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Yesterday Miesk5 stated that he would be away for a week. Perhaps this thread will be a little helpful.

http://broncozone.com/forums/index.php?s=&...ost&p=76967

Other than possibly gleaning some info out of it, be sure to check your conenctors to the O2 sensors... clean and tight.

Look for vacuum leaks, and exhaust leaks before the O2 sensors.

6-8 startups and warms ups should clear the CEL, but the code may stay in memory for 40-80 startups.
Thx for the reply, Joe. I'll check connections and vac leaks. Maybe some dust from sanding screwing with the MAF now that I think of it.

 

bko4x4er

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how many 02 sensors does a bronco have?

on my 92 there is one on the puipe right from the manifolds...is therer another?

 

BroncoJoe19

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I am 95% positive there is only one.

On my 98 windstar there are four, one before and after each CAT, but I am pretty sure that even the '96 Broncos only had one.

 

Roadkill

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Your slipping a little, Joe. :D /emoticons/[email protected] 2x" width="20" height="20" /> The '96 (or at least mine) has three O2 sensors; one on each side of the Y pipe before the cats and one more after the cat. I haven't looked under a '92, but I would check those same locations on the '92. If there is more than one, that is where they will be.

 

BroncoJoe19

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Your slipping a little, Joe. :D /emoticons/[email protected] 2x" width="20" height="20" /> The '96 (or at least mine) has three O2 sensors; one on each side of the Y pipe before the cats and one more after the cat. I haven't looked under a '92, but I would check those same locations on the '92. If there is more than one, that is where they will be.
Your slipping a little, Joe. :D /emoticons/[email protected] 2x" width="20" height="20" />

LOL Hehehehe... you have NO idea! :) /emoticons/[email protected] 2x" width="20" height="20" /> , although I did put in that 5% wiggle room :-"

Autozone lists both.. before CAT and after CAT O2 sensors for a '90. So it would seem that I have at least two! Yet the Haynes manual's wiring diagrams only shows one. Also my 1990 EVTM only lists a single HEGO (Heated Exhaust Gas Oxygen Sensor) located in the exhaust pipe ahead of the catalyst.

I wish my truck was here... I'd go out with a flashlight and crawl under it to count.

I suspected that the '96 broncos may be different in that they have a OBD II computer system, but the Haynes manual I referenced stated that the wiring diagrams for the 92-96 are the same, and those only list a single instance of the O2 sensor.

My guess at this point is that the OBD I systems have one HEGO, and the 1996 OBD II systems have three O2 sensors, (four if there are two Cats).

That's my story... and I'm sticking with it. :) /emoticons/[email protected] 2x" width="20" height="20" /> Well, at least unless I am proven wrong :|

 

bko4x4er

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Your slipping a little, Joe. :D /emoticons/[email protected] 2x" width="20" height="20" />

LOL Hehehehe... you have NO idea! :) /emoticons/[email protected] 2x" width="20" height="20" /> , although I did put in that 5% wiggle room :-"

Autozone lists both.. before CAT and after CAT O2 sensors for a '90. So it would seem that I have at least two! Yet the Haynes manual's wiring diagrams only shows one. Also my 1990 EVTM only lists a single HEGO (Heated Exhaust Gas Oxygen Sensor) located in the exhaust pipe ahead of the catalyst.

I wish my truck was here... I'd go out with a flashlight and crawl under it to count.

I suspected that the '96 broncos may be different in that they have a OBD II computer system, but the Haynes manual I referenced stated that the wiring diagrams for the 92-96 are the same, and those only list a single instance of the O2 sensor.

My guess at this point is that the OBD I systems have one HEGO, and the 1996 OBD II systems have three O2 sensors, (four if there are two Cats).

That's my story... and I'm sticking with it. :) /emoticons/[email protected] 2x" width="20" height="20" /> Well, at least unless I am proven wrong :|
well see i have cut off everything after my first cat. i cut off my muffler and second cat.

all i have now is pipe from the manifolds then a cat. then nothing after that cat.

all i see is one sensor right before that cat on the pipe. i have already replaced it bcuz i get like 7 mpg and i was tuneing it up.

 

miesk5

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to confirm our pal Roadkill's info...

btw, we have 3 O2 Sensors in our 96 5.0/5.8; One in each exh manifold pipe and one before cat

Locations, 96 Bronco, F Series, Explorer, Expedition, etc. Source: by Ford it shows the 4th for CALIF SMOG

(freaked-out Calif Emission Broncos have 4 O2 sensors)

my Ford EVTM;

http://www.broncolinks.com/gallery_images/...rlocations965.0

EDIT; site went down due to server issues for a few and didn't save this here;TSB

01-9-7 DRIVEABILITY - HO2S (HEATED OXYGEN SENSOR), CATALYST, AND FUEL SYSTEM MONITORS - SERVICE TIPS - OBD II VEHICLES ONLY

(partial TSB; see my site for full; here it is) For P0141 - CHECK:

Blown fuse

Short to VPWR in harness or HO2S

Water in harness connector

Open VPWR or GND circuit; VPWR = Vehicle Power (Battery Voltage)

Low battery voltage

Poor electrical connections from PCM to HO2S sensor

HO2S heater

PCM (not likely)

HO2S sensors are not likely to be the cause of adaptive DTCs P0171, P0172, P0174, P0175: Most warranty-returned HO2S sensors (replaced for these DTCs) are found to function normally. Additional related DTCs will normally be present if there is a concern with the HO2S sensors. Do not replace an HO2S sensor unless verified through pinpoint diagnostic tests found in the PC/ED Service Manual.

DTCs P0171, P0172, P0174, and P0175 are not related to downstream HO2S sensors: When diagnosing a vehicle with a MIL On and DTC(s) P0171, P0172, P0174, and/or P0175 in continuous memory, do not replace the downstream HO2S sensors. These DTCs have no connection to the downstream HO2S sensor function nor its diagnosis for faults. Always verify the vehicle concern, then perform the pinpoint diagnostics from the appropriate PC/ED Service Manual.

Diagnosing lean conditions and lean DTCs P0171, P0174: Freeze Frame Data can often help to identify the type of lean condition, even if the fault is intermittent, by indicating how the vehicle was being driven when the fault occurred. Diagnosis of lean conditions and lean adaptive DTCs can be difficult, especially if the concern is intermittent. Verifying the concern is extremely important. There are different types of lean conditions. The ability to identify the type of lean condition causing the concern can be crucial to a correct diagnosis. When DTCs P0171 and P0174 are both present, there is a strong likelihood of another concern being present:

Vacuum leaks/unmetered air: In this type of condition, the engine may actually run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is typically caused by air entering the engine through an abnormal source (opening), or due to a MAF malfunction. In this situation, the volume of air entering the engine is actually greater than what the MAF is indicating to the PCM. Vacuum leaks will normally be most apparent when high manifold vacuum is present, during idle or light throttle. If Freeze Frame Data indicates that the fault occurred at idle, a check for vacuum leaks/unmetered air when the engine is cold might be the best starting point.

Examples: Loose, leaking or disconnected vacuum lines, intake manifold gaskets or O-rings, throttle body gaskets, brake booster, air inlet tube, stuck/frozen/aftermarket PCV valve, unseated engine oil dipstick, MAF reading lower than normal, etc.

Insufficient fueling: In this type of condition, the engine may actually run lean of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This condition is typically caused by a fuel delivery system concern that restricts or limits the amount of fuel being delivered to the engine. This condition will normally be most apparent when the engine is under a heavy load, when a higher volume of fuel is required. If Freeze Frame Data indicates that the fault occurred under a heavy load, a check of the fuel delivery system (checking fuel pressure with engine under a load) might be the best starting point.

Examples: Low fuel pressure (fuel pump, fuel filter, fuel leaks, restricted fuel supply lines), fuel injector concerns, etc.

Exhaust system leaks: In this type of condition, the engine may actually be running near stoichiometry (14.7:1 air/fuel ratio), but the exhaust gas mixture will be lean. This condition is caused by oxygen-rich air entering the exhaust system through an external source. This condition will cause the exhaust gas mixture to be lean, even though the actual combustion in the engine may not be.

Examples: Exhaust system leaks upstream or near HO2S, malfunctioning Secondary Air Injection system.

MAF concerns: If a MAF concern is suspected, see TSB 98-23-10. (MIESK5 NOTE; see my TSB info here for this TSB) - do you have a dirty air filter or an over-oiled K&N?

Checking fuel pressure: Check fuel pressure with engine under a load when diagnosing a lean concern. A partially plugged fuel filter can be difficult to detect and can be easily overlooked if fuel pressure is only checked at idle. The same is true for other types of fuel supply concerns (e.g., bent or kinked lines, degraded fuel pump).

At idle, an engine requires only a small volume of fuel. Due to the fact that there is a small volume of fuel needed at idle, a restriction in the fuel supply line in many cases will not cause the fuel pressure to be low. When the vehicle is under a load, the engine requires much more fuel than at idle. Under a load, a restriction in the fuel supply line will prevent the high rate of fuel flow that is needed to maintain the correct fuel pressure.

 
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bko4x4er

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so i checked and yes i only have one sensor . i just dont get it though, i have replaced everything

-spark plugs

-wires

-cap

-rotor

-ignition coil

-o2 sensor

-air filter

-oil change and filter

i have the right amount of oil, coolant, but i was running low on tranny fluid

and im still gettting 7-8 mpg.

i am stock with 33s

302

 

BroncoJoe19

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BKO did you check for vacuum leaks?

Did you pull codes?

Vacuum leaks can cause all kinds of problems.

Pulling codes can help us narrow down the possiblities.

 

bko4x4er

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to tell the truth i really dont feel like going through the whole thing. i dont completely know how to do it first off. and i do have cracks down the side of both my manifolds, that are like 4 inches long. dont know if that comes into play.

 

HardMaple

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to tell the truth i really dont feel like going through the whole thing. i dont completely know how to do it first off. and i do have cracks down the side of both my manifolds, that are like 4 inches long. dont know if that comes into play.
Can you feel exhaust leaking from these cracks with the engine running? If so, then YES they are more than likely the cause. They will also warp your valves. If there is no exhaust leaking out, then maybe they are just casting marks.

 

bko4x4er

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Can you feel exhaust leaking from these cracks with the engine running? If so, then YES they are more than likely the cause. They will also warp your valves. If there is no exhaust leaking out, then maybe they are just casting marks.
yes you can feel air comming from both cracks on each siode

 

HardMaple

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yes you can feel air comming from both cracks on each siode
That's the answer then. You will never get a normal O2 sensor reading with any sort of exhaust leak above the sensors. And if the leak is large enough, it could lead to damaged valves. You can either replace them (new or junk yard), look for headers, or get them fixed (brazed or Lock-N-Stitch technique). Either way, you need to resolve these leaks before continuing on with the O2 sensors.

 

bko4x4er

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That's the answer then. You will never get a normal O2 sensor reading with any sort of exhaust leak above the sensors. And if the leak is large enough, it could lead to damaged valves. You can either replace them (new or junk yard), look for headers, or get them fixed (brazed or Lock-N-Stitch technique). Either way, you need to resolve these leaks before continuing on with the O2 sensors.
well after i replaced the o2 sensor...the check engine light went off for good.

but i actually think that if i was to take the manifolds off they wuld fall into two pieces. i think the crack has gotten big enough all the way aound to where the manifold is now in two pieces.

 

michibronc

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Sorry guys, haven't had much time to play with my rig lately. I drove it about 400 miles with the CEL illuminated - seemingly no problems and I got 16 mpg, so that makes me wonder....

I've cleaned the MAF sensor (the truck does have a heavily oiled K & N air filter -they really soak them when you get em new), checked for vac leaks (couldn't find any), replaced the PCV valve, replaced my oil filler cap which had previously cracked and had a mystery piece of something rattling around in it.

Have driven about 500 miles altogether now - CEL still illuminated. I need to go to azone and get the codes cleared to see if they come back. I also need to change my fuel filter - it looks old. I lack the tool to disconnect the lines.

I'll check the connections and change the fuel filter, erase codes and check back asap. Thanks for all your help, fellas.

Oh yeah,

1. What's the tool called again that you use to disconnect the fuel lines from the filter?

and

2. What fuses should I check to see if they are part of the problem? Just the ones near the drivers seat or are there more?

 

Yardape

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When I bought "the tool" for my Bronco I'm pretty sure all it said on the package was Fuel line and AC line seperator. Came with an assortment of sizes. Any local parts department that sells tools should know what your talking about.

 

michibronc

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Thanks, Yardape. OK - gonna sound kind of stupid here. I bought the tool to change the fuel filter - now how do I use it! Do you clamp the tool around the fuel line or do you clamp it around the nipple on the fuel filter itself and slide it into the fuel line fitting. Damn I wish I would have taken auto shop in high school.

When I bought the tool I had the codes cleared. Nothing came back yet, but I've only driven it about 10 miles. There were two codes most recently thrown....

p0141 (O2 sensor heater circuit malfunction)

and

p1131 (Not sure on that one) but I think it means that an O2 sensor isn't switching correctly.

p0174 didn't come back and that's after 400 miles of driving.

 
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