Contour Enthusiasts Group Archives Forums General Troubleshooting Codes P0420 & P1151

OK, this is the 2nd time I've gotten these. The first time around, I replaced the offending exhaust manifold and O2 sensor under (barely) warranty. Now again!? Same manifold & same O2 sensor. No warranty now. (Waaay over the fed. catalytic warranty)

P0420, as I understand it, is a plugged pre-cat right? And P1151 indicates a lean condition, right?

Am I driving wrong or something, what would cause this twice?

Also, since I've pulled these codes, the car will sometimes stall under hard decelleration.

FYI: 98.5 SVT. Only mods are MAF adapter & K&N and removed resonator.

TIA,
-Chuck

Neither of those codes are indicative of an intake manifold leak.

Specify how old the exhaust manifold and the O2 sensors are.

Steve

The manifold and sensor were both replaced late in '02 (around Nov. IIRC).

In the last month or so, I've reset the P0420 code maybe 5 or 6 times. It wasn't until last week that I pulled the P1151. Just 2 days ago it started stalling under hard decelleration. The RPM's just PLUMMET.

I've had the K&N on for a little over a year. The first time I had these problems (prior to the manifold/sensor replacement) I was running the stock intake.

What makes this more aggravating is that my mechanic claims that those codes "don't even exist" for this car. WTF!?

I'm planning on checking/cleaning or replacing the following:

MAF, IAC valve, EGR valve, idle air bypass, Air filter.

MAYBE replacing the O2 sensor.

Hopefully some combination of the above will clear up the low idle/stalling problem.

I suppose I'll have to bite the bullet and get some MSDS headers to replace the plugged pre-cats (MUCH cheaper than stock manifold!) - unless, of course, I can find some good, cheap, pre-gutted manifolds- no more pre-cats to clog and no more sensor to foul.

Given the above, could my car really be running lean- per the P1151 code? Or is it still "pending"?

TIA,
-Chuck

ttt

Find a new mechanic. These are among the most common codes on Contours seen here.

The P0420 is not for a "plugged" pre-cat, it indicates that the pre-cat is not doing its job. Big difference.

Were both exhaust manifolds replaced or only one? If only one, which one and was the original code a p0420 or was it a p0430? Perhaps it was a 430 and the dealer only replaced one pre-cat, now the other has failed (speculation).

Stalling under hard acceleration frequently is due to fuel delivery problems, weak spark, or a dirty MAF.

The P1151 is a weak front upper O2 sensor. Replace it for this code.

The P0420 is for Bank 1 (firewall side). You can putz around with all the other stuff if you want to, but only a new exhaust manifold will properly fix it.

Any exhaust shop can check for clogged cats. Heck, you can buy the guage off of e-Bay for $20 and check it yourself.

If you go with either gutted pre-cats or headers that don't include cats, you will need to get a set of MIL eliminators to keep the CEL from coming on with 420 and 430 codes.

Low idle and stalling are more likely related to the IAC.

Steve

Thanks for the quick reply Steve,

First, a couple of things: When I originally went to the dealer to replace the 0420 manifold- the firewall side, somehow the techs (@ Hollywood ford) pulled a 0430- the front. I have never pulled this code with my scanner. They replaced the front and cleared the code. I have this documented on the service record. Now, this whole time I was thinking "OK, I'll bring it back when it spits out the 0420 again". Which it did within a week. The rear was replaced as well- also documented.

So as far as I know I've got 2 new manifolds (new as of Nov. '02). Is there something, ANYTHING, that I could be doing that's F'ing up that rear manifold?! I mean c'mon, TWO bad rear manifolds in just over a year?

As for the 1151- I'm just glad it's not that b*tch on the rear again! My knuckles were shredded and bruised for weeks after that!

Thanks again though,
-Chuck

I am getting the p1151 code. Where exactly is the front upper o2 sensor?
Mike Dickenson