CEL codes 176, 136... FIXED | Ford Explorer Forums - Serious Explorations

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CEL codes 176, 136... FIXED


Well-Known Member
May 16, 2009
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City, State
Fayetteville, Ar
Year, Model & Trim Level
'93 X Sport
Getting CEL CM code 176, and a KOER Code of 136...

Oxygen sensor not switching/system lean Left or Front HO2S - Fuel control

Oxygen sensor not switching - system is or was lean Left or Front HO2S - Fuel control

I need to swap my O2's to test and see if it's a real lean issue or a bad O2 (seeing if problem follows sensor or location) just posting this up for anyone who get's these codes in the future, and I'll update with my experences.
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As strange as it seems, it appears to be this that was causing the codes.....


After puting the muffler back into the tail pipe, I haven't thrown a Check Engine light yet. It's the only thing I've done since I last got a CEL, and it didn't throw one on the 15 mile trip to work, nor the 20 mile trip around town at lunch. Since I've owned the truck that's the longest time without it throwing the 176 code.

All I can come up with is it's a back presure thing. That the exhaust has been loose (and it just slid right back into the tail pipe, nothing is "holding" it in there except gravity) and that it has been lowering the back presure because of the loosness and causing the O2 on the left/front to think the truck is running lean.??!??

Anyway, I don't think it's the actual connection in the pic that was causing the problem, I don't think the tail pipe section would make that much difference. But that section from the muffler to the cat has a connection that "piviots" and that also is somewhat loose. I think I got a better connection on it when I put the muffler back into the tailpipe and I think that has caused my codes to stop.... For now at least. I'll post up with more info if they come back. I'm going to have my exhaust done right and we'll see then for sure!

I am having CEL on my 2003. I found out that its the O2 sensors. Has anyone changed these things out, and is it real difficult?

Ok, it's confirmed, it WAS the loose exhaust system that has been causing all my issues with CEL Code 176/136. It came loose again off roading in a dry creek bed thanks to a clearance issue and rouge exhaust removing rock.

Light came back and acted like it always used too. Spit, duct tape (not really), a clothes hanger, and a prayer has the exhaust back on until i can get it all fixed at a shop, but the light has not come back on for 400 miles.

Problem solved! :salute:

that is weird because I JUST got my muffler put back on Friday, I never had a light.. Its had been off 6 months

well, the muffler is back off now, course it's also sitting at the end of an off road trail from hell and I'm not even sure I can get a recovery rig in there, so it might be a bit before I see if it comes back or not.....

Gotta bring this one back from the dead, so, over the last two months the light has been off and on, depending on the status of the exhaust. If it was loud and leaking, I had a light, if it was quiter and not leaking...no light. I would fix it and it would work OK for a couple of days, then get loose again.

So anyway, fixed the exhaust the other day..... Now I get the light anytime I drive over say 45-55 mph for any time. Just pulled my codes, and it's the 176 code again.

So, I'm hoping when I'm doing my oil change this weekend that I can swap the O2 sensors out and see if the problem follows the sensor or the location.

Any other ideas?

If it says O2 sensors thats probably the culprit. You might score some 02 sensors from the junk yard to try out before dropping the coin to replace em?

Going to swap em first, it's say LEFT side is the one with issue, if I swap and it starts saying RIGHT side... then I have my answer!! LOL...

On that note... Is left side Drivers side or Passenger side???? Thanks!!

The left/right convention is from the driver's point of view sitting in the driver's seat. So left refers to the driver's side and right refers to the passenger side.

That surprises me, I had always assumed it was the O2 sensor right before the collector on the passenger side causing the issues. Seems to me if it was exhaust related, then the one closest to the problem would be the one causing trouble.

But it's the one farthest away.... will swap tomorrow and we shall see what's what. I was really hoping when I got my exhaust fixed (pro fix, as in muffler shop not me with more coat hangers) that this annoying issue would go away. Doesn't seem to affect anything, just annoying at night to have the light always on.

ok, so as this post shows I had my codes and they seemd to be related to the exhaust being loose or not. And this held true for 4 months. Then when I finally got the exhaust fixed...the light would come on when going over 50 mph...

So I went to swap out the O2 sensors. Was going to swap the left and right sensors to see if the problem followed the sensor, and replace if it did. However I couldn't get the Right front O2 sensor out. The left (problem one) came right out with a little work.

In the end had to call it a day before I could ever get the right one out, so I put the left one back in...

Haven't had a CEL since.....

Seems just unscrewing it and screwing it back in fixed it....somehow..... loose connection? Clogged up inside?? Don't know, but no CEL anymore ever!