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P0170 Fuel Trim Malfunction (Bank 1)??

05-27-2005, 09:49 AM
Hi guys, one quick question. I have a 98 Windstar 3.8, the SES light came up about a week ago. i went to check the code at my local Autozone and the code came up to be:
P0170 Fuel Trim Malfunction (Bank 1) (as read from
now what exactly does this mean? the Autozone guy said it's one of the oxygen sensors. Should i go ahead and change all sensors or can it be something else?... thanks for you help guys.

05-27-2005, 10:09 AM
"Change Oxygen Sensor" seems to be the common advice from Autozone.

I am not familiar with that particular code but it seems like it could be the O2 sensors but one should always investigate a bit more before playing hit and miss. Grab a Haynes or something and try taking some voltage measurements and compare with the bank 2 sensor readings. (Careful the o2 sensors and exhaust will get hot).

You can swap to see if the code follows the sensor or stays in the bank 1 portion of the vehicle. (Be careful as I have heard of someone removing the threads in the exhaust with an o2 sensor)

05-27-2005, 11:01 AM
DRW has some good advice on how to isolate the problem. There is no P0170 trouble code for your vehicle(according to the Ford manual). P0171 is bank 1 at lean correction limit. This is the side #1 spark plug is on. P0174 is bank 2 at lean correction limit(the other side).You need to look for anything that will affect only one bank, such as exhaust leak, engine misfire, weak injector. Do not replace sensors until you have thouroughly checked out as to why the code appears. Usually an O2 sensor will set a code for itself.

05-27-2005, 02:24 PM
thanks for the quick response guys. I was a bit skeptical about that error code, the Autozone guy didn't seem like he wanted to help and just gave me the code without letting me check the scanner over before he unplugged it (I'm going to get one this afternoon). i've read about the p0171 code in this forum so I might refresh a bit more and will check around the engine over memorial day weekend. have a great memorial day guys and thanks again.

05-28-2005, 06:27 PM
Most oxygen sensors that are replaced do not solve the problem. Moving the upstream sensors from side to side will help to eliminate the question. Also, a look at the sensor (removed) to see if it has a green stain on it will tell you if you have a coolant leak. The most common cause of coolant leak into the cylinder is from a leak in the lower intake manifold. If you do end up replacing oxygen sensors (I don't think you need to as there are lots of codes for them), use Motorcraft brand... You can get the Motorcraft sensors from for a good price.

As always....look around for a vaccum leak.

The Isolator bolt TSB does NOT apply to the Pre-99 do not worry about that one.

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