Code PO170 Fuel Trim Malfunction Bank 1 on '99 ej22

[Scottbaru]

Possibly a dirty injector? Do these codes clear themselves eventually if the problem goes away? The guy at Autozone said they're not allowed to clear them. I didn't press the issue, I think these codes clear themselves. First step I'm running Techron injector cleaner. 77k on this '99 ej22, no service history, recent new clutch.

[Legacy777]

You can pull the ECU fuse for 30 min or so, and that should reset the ECU, effectively clearing the code.

 

The light will go off by itself usually, but the code should not disappear from the memory without it being manually cleared or a loss of power.

[Scottbaru]

Thanks for the response. Will that work for an OBDII? I'll give it a try anyway, the EFI fuse I assume?

[Scottbaru]

No dice, an hour without power and only the radio has lost memory. Maybe it's time to pull injectors.

[99obw]

My understanding of this code is that the ECU has adjusted the long-term fuel trim all the way to one of it's stops (rich or lean) in an attempt to correct a perceived mixture problem. The problem can be related to air supply, fuel supply, or sensors related to mixture(MAF, MAP, IAT, O2).

 

It would be helpful to read the fuel trim using a scanner to see which direction the ECU has adjusted it. If it's adjusted rich (perceived lean condition) it might be caused by an air leak somewhere. When was the last time the fuel filter was changed? Oh, I see, no service history. Plugged fuel filter would cause a uniform fuel delivery problem. If the trim is set lean (perceived rich condition) I would suspect air filter or a faulty sensor(s) or injector(s).

 

I would start with a fuel filter, air filter, run a couple tanks of Techron, and check for air and vacuum leaks. If that doesn't work I would start thinking about the sensors. I would try these inexpensive things first, as they are necessary regardless due to not having a service history. If that doesn't work you may need a tech that has a scanner.

[Scottbaru]

Thanks, that's very helpful info. I normally change all fluids and filters when I buy a car, but I broke my leg just before buying it, and I'm just now getting caught up on house and car stuff. I guess it's time to give it some attention.

[Scottbaru]

Fixed! I found the hose clamp that holds the intake plumbing to the throttle body loose, vacuum leak. Interestingly, the A4 turbo quattro also came up with a CEL, we found some vacuum lines deteriorating, that was the problem.

[99obw]

Woohoo!!

[ferp420]

RE: PO 170 Code, in our 1997 Subaru Legacy Outback.

We had the PO 170 code show up 5 times in a row!  First, we replaced the O2 sensor.  Code came back. Faulty sensor, replaced it. Code came back on.

Cleaned MAS (Mass Air Sensor) and replaced air filter, it was filthy. Code came back again!  Finally went to Subaru Recycled Parts yard, got a used

Mass Air Sensor for $45,  just drove the car home over 100 miles and no code!! Yay! Also, we got some other codes in between all this, which were due to hoses that had come off, so do check all hoses as well for vacuum leaks.

Edited April 2, 2013 by ferp420