p0174 and p0420

[mikeymoby]

new cat and new 02 sensors and no they are after market, i have a snap modis so i watched the 02 sensors going down the road and there they were acting fine none were sticking on high or low they read 127.991 ma then -127.91 ma , they jumped high low and never stuck on either one, by the time my ride came to a end there was two codes pending p0174 and p0420, i can not get the engine light to stay off, and please dont tell me you cannot us aftermarket parts because everone else in the world uses aftermarket parts.

[AWDFTW]

Thread moved to correct forum.

[AWDFTW]

Furthermore, let's have some actual details please?

Vehicle?
Miles?
Known service history?

Why did you replace the cat? They rarely fail.

And I hate to tell you....but aftermarket cats and O2 sensors....typically are not gonna last long or work right on these cars.

[mikeymoby]

it is a 2004 outback with a 2.5l 4cyl last year the check engine light came on and said the cat was bad, replace cat and both o2 sensors, 120000 miles no exhaust leak and o2 sensor go high low they switch back and forth like thay should. that makes no sense about after market not working if the computer is that senceitive then one little hicup wil turn the light on.

[cardoc]

One, you are looking at the incorrect sensor data. You need to look at the AF sensor Lambda data. That is what the ECM uses to determine rich or lean conditions.

Two, the sensor is reporting too lean, so looking at the Lambda data will give you an indication based on the voltage output of the sensor. If you are unsure of the sensor function, you can force a rich condition simply by spraying in an accelerant into the intake while its running and watch for the voltage to drop. If you used a "universal" sensor, that may be the issue.

Three, things that make an engine run lean and cause a P0174 or a P0420 are fuel delivery, vacuum leaks or incorrect AF, MAP or MAF data.

So, what you need to do is watch the correct data stream from the AF sensor and LTFT calculations. The ma values you are watching is the STFT waveform data. Check the fuel delivery. Check for vacuum leaks. and varify your air flow to be correct.

For now, ignore the P0420 and concentrate on the AF and fuel trim.

And read through here: P0420 Diag

[mikeymoby]

cardoc thank you thats what i was looking for good info on my proplem i needed to now i was looking at the wrong thing, it not like a gm were it is what it is, ford sometimes can be hard to find there proplems so thanks again i will checkout the things you were talking about, i have a modies from snapon, so i hopefully can figure it out.

[cardoc]

That Modis is a slow transfer rate, so if you force a condition, wait for the data from the scanner to catch up.

[mikeymoby]

the tps starts out at 16.9 % will that make for the two codes and yes the transfer rate is real slow