Contour Enthusiasts Group Archives Forums General Troubleshooting Code P1151

'96 Mercury Mistake
V6 2.5L
Miles on dometer - alittle over 91,000

Problem: Check Engine Light comes on in during in town driving and goes off on the highway.

I drove over to a local AutoZone and they tell me the code is P1151.
Lack of HO2S21 Switch.
Sensor Indicates Lean.

AutoZone said it's the O2 Sensor (Bank 1) on the passenger side which needs to be replaced. ( I have no clue! )

Last year FORD diagnosed a P0420 code problem.
I had the dealership replace the Right Front Cat. Convertor and Exhaust Manifold Assembly. I believe they also replaced a sensor along with this.
FORD charged $491.13 to do this.
Lincoln Mercury was asking to charge even more. ( They always do - "It's a Mercury... and they cost more to work on." LOL! )

I guess what I am asking is... do I need to replace this O2 sensor if the light is going out on it's own when I get out on the highway? I have read where there could be a vacumm leak. I'm wondering if this is my problem because the JACKA$$ who last changed my oil and air filter lost two of the clams on the intake housing. I noticed this after I got the car home and felt a vibration while in reverse. I have inspected the housing and it seems to have a good seal... but I really can't tell. The two clams are gone and they have no idea how they could have lost them. Hmmm - right...

I need the experts help here... you have never let me down yet.

If I do have a vac leak, could it be because of the missing clams on the intake housing?
If this is the case, can these be purchaced without having to buy the complete housing?

If you're talking about the clips on the air filter housing, then no. I do not expect this would cause the car to run lean.

You are getting un-metered air into the engine, which means a leak after the MAF, from the accordian hose to the bottom of the intake manifold. One of the hoses or gaskets may be cracked or worn through.

OK, I've checked the accordian hose and everything I can see and listen to. I don't hear any hissing.

I have kept this car in extreme clean condition... so I would see any cracks. It all looks new.

So, you are saying it could be a gasket or it could in deed be the O2 sensor?

Thank you.

You have been a big help.
I'm going to get out the Haynes Manual and read everything and then go look again.

Thanks again.

OK, I have checked all the vac hoses ( that I know of ) and can not find any cracks or leaks. I did this by looking and listening to them while the car was running. I've followed all the rigid tubes around from the UIM and they all look good. Everything is connected. The small (white in color) hose down by water pump belt appears to be fine and several inches away from anything moving - no cuts. There doesn't seem to be any cracks anywhere and my UIM gasket appears to be fine - all the bolts are tight. No drips or leaking.

Still I get the same results... in town driving the CEL will come on. Highway driving the light goes out after a few minutes. When the CEL comes on the car shifts harder and is very sluggish - drinking lots of gas.

Any other suggestions?

I just reviewed a few other posts with this problem. Other than leaks, it can be a failed sensor, or an electrical problem.

To troubleshoot, one CEGer swapped his front/rear O2s to see if the problem followed the sensor. If so, replace the sensor. If the problem stays on the same bank after switching the O2s, then the problem is either electrical or a leak into that bank.

Good idea.

I'll try that.
Thanks