Cel on again po430

[SnTx4]

Ok, CEL is on again. Code po430. The light will stay on for weeks and then go out for weeks. As a shot I thought I'd try an o2 sensor. When I search and read some posts, some say just replace cats, or replace upstream, or replace downstream. So just wondering which sensor to start with. I don't have a way to do a live scan, so just figured I put one in and see what happens. 98 5.0.

Travis

 

[SoNic67]

I did replace the UPSTREAM O2 sensor and fixed the problem.
I thought it was cheaper than replacing the cat and finding out that didn't help.

The cat efficiency is monitored by the difference between the upstream and downstream O2 indications. If the upstream O2 is worn out but not completelly bad, it will swing too slow the output and will "look" like the downstream signal - so the PCM thinks that the cat is not efficient.

The rear O2 sensor will just give a "bad" code directly. This is because the signal past a good cat will be slow to change anyway, so a worn out downstream sensor will not make a difference in the cat efficiency logic.

Now, sure, it can be a good O2 and the cat is really bad... You will loose only 35$ for the new O2 sensor. That should be replaced anyway periodically.

 

[SnTx4]

Thanks. I ordered one for less than 30, should be here tomorrow. It would be nice if that does the trick. I only have 125k, I know its possible for the cats to be bad, just wouldn't think so.

 

[SoNic67]

My Sable had 140k miles when that happend. I drowe it like that till 160k when I replaced the O2 sensor and is still OK (almost 180k now). My area does not require emission testing so I was not in a hurry to try to fix it (I thought for the longest time it was bad cat for sure).
The O2 sensors in my Duratec Sable are identical with the ones in 5.0L (used Bosch since that was OE in there).

 

[SnTx4]

Replaced upstream 02 today, guess we'll see what happens.

 

[SnTx4]

Alright, looks like that did the trick. Gone about 400 miles and no CEL.

 

[SoNic67]

Glad that helped Knock on woood.

 

[swetrid]

Ford has tsb for pcm update, do this first!
Printable View (29 KB)
TSB
04-7-5 DRIVEABILITY - MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATED - DIAGNOSTIC TROUBLE CODES (DTC'S) P0420 AND/OR P0430

Publication Date: April 6, 2004

FORD: 1998 EXPLORER
MERCURY: 1998 MOUNTAINEER


This article supersedes TSB 03-25-1 to update the vehicle lines.

ISSUE:
Some 1998 Explorer/Mountaineer vehicles equipped with the 5.0L engine may exhibit a malfunction indicator lamp (MIL) on with diagnostic trouble code(s) P0420 (Catalyst System Efficiency Below Threshold - Bank 1) and/or P0430 (Catalyst System Efficiency Below Threshold - Bank 2).

ACTION:
To service, reprogram the powertrain control module (PCM) to the latest calibration using WDS release B28.3 or higher. Replacement of catalysts is no longer necessary to address the most common causes of this condition.

Obtain an Authorized Modifications Decal (FPS 8262 - obtainable through DOES II, 25/pkg) and list the date, dealer number, and summary of modifications performed. Select a prominent place adjacent to the Vehicle Emission Control Information Decal suitable for installing the Authorized Modifications Decal. Clean the area, install the decal, and cover it with a clear plastic decal shield.

AUTHORIZED MODIFICATIONS

THE FOLLOWING MODIFICATIONS HAVE BEEN MADE:
Reprogrammed Powertrain Control Module (PCM) Per TSB 04-7-5



THESE MODIFICATIONS HAVE BEEN APPROVED, AS APPROPRIATE, BY EPA AND CARB.
DEALER NUMBER:------------------------------------------DATE:

CHANGE AUTHORITY:

FPS 8262 9/78 FORD MOTOR COMPANY PRINTED IN U.S.A.





OTHER APPLICABLE ARTICLES:
NONE

WARRANTY STATUS:
Eligible Under Provisions Of New Vehicle Limited Warranty Coverage And Emissions Warranty Coverage


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NOTE: The information in Technical Service Bulletins is intended for use by trained, professional technicians with the knowledge, tools, and equipment to do the job properly and safely. It informs these technicians of conditions that may occur on some vehicles, or provides information that could assist in proper vehicle service. The procedures should not be performed by "do-it-yourselfers". Do not assume that a condition described affects your car or truck. Contact a Ford, Lincoln, or Mercury dealership to determine whether the Bulletin applies to your vehicle. Warranty Policy and Extended Service Plan documentation determine Warranty and/or Extended Service Plan coverage unless stated otherwise in the TSB article. The information in this Technical Service Bulletin (TSB) was current at the time of printing. Ford Motor Company reserves the right to supercede this information with updates. The most recent information is available through Ford Motor Company's on-line technical resources.

Copyright © 2004 Ford Motor Company