96 winstar codes?

My 96 3.0 winstar with 100,000+ miles while on a trip to Florida last year had poor gas mileage 14-15 mpg. Engine light came on, had codes read and P0131 and P0151 came up (O2 sensor, Lean). We had two kayaks strapped on top. One year later did the same thing. Poor gas mileage (16.5 avg mpg), engine light came on, codes read the same. Also, engine light came off and gas improved while traveling around for 10 days (19.5+-mpg) going 100 miles per day. Got back on interstate and while on trip home mileage dropped and engine light came on. Any one have some sugestions? 02 sensors have not been changed, I bought them but could not get one off. The van now has 135,600 miles on it.

Those codes indicate that your upstream (before catalytic converter) sensors are giving a voltage that is "out of range, voltate LOW" for bank #1 (P0131) and Bank #2 (P0151).

This is different from lean (P0171 and P0174).

The codes are universal.....same for all years......3.8L and 3.0L engine.

Can be caused by crossed signal return wiring or a bad electrical connection. I would first try unpluging each sensor (1 at a time) and verifying that there is not water / oil inside the connector....
Clean as needed. Reconnect.

Carefully inspect the wires as they go from each oxygen sensor....and verify that they do NOT come in contact with any hot exhaust part. Follow the wires as far as you can...and move any wire that is touching an exhaust part away. Possible as it happens when you are running a little harder for a longer time.


This also can be caused by contaminated oxygen sensors (they generate a voltage from a chemical reaction). Are you losing any coolant?....would be odd cause for both sensors at the same time.

Those codes indicate that your upstream (before catalytic converter) sensors are giving a voltage that is "out of range, voltate LOW" for bank #1 (P0131) and Bank #2 (P0151).

This is different from lean (P0171 and P0174).

The codes are universal.....same for all years......3.8L and 3.0L engine.

Can be caused by crossed signal return wiring or a bad electrical connection. I would first try unpluging each sensor (1 at a time) and verifying that there is not water / oil inside the connector....
Clean as needed. Reconnect.

Carefully inspect the wires as they go from each oxygen sensor....and verify that they do NOT come in contact with any hot exhaust part. Follow the wires as far as you can...and move any wire that is touching an exhaust part away. Possible as it happens when you are running a little harder for a longer time.


This also can be caused by contaminated oxygen sensors (they generate a voltage from a chemical reaction). Are you losing any coolant?....would be odd cause for both sensors at the same time.


Makes sense. I'll try that. Would you change O2 sensers?

I would change the one you can remove and see if a code disappears, they are overdue if they have never been changed. There are 4 and we are talking about the 2 upstream from CATs.

That will have to be your call.
It is NOT normal for both sensors to fail like that.....unless something contaminated them.....Which is rare now-a-days.

If you do replace....I would replace both upstream sensors.
I would get the Motorcraft brand....which you can get at www.rockauto.com for a reasonable price.

Reason to replace as a pair.....as they age...the switching speed slows down. You want to have the same switching charactoristics for both cylinder banks.

The downstream sensors are only used to monitor the catylitic converters to make sure that they are working.