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Getting OBD-II code P1131 on 1999 Ford F150

I have 1999 ford f150 4.6L v6, standard 5 speed transmission, 216000 miles. Had a new fuel pump (the whole assembly … original equipment not aftermarket) installed about 3 months ago (mid-June 2012) and changed the fuel filter as well.

Mostly I drive it only once per week … just long enough to get everything warmed up (at least 20 minutes or so). So, since the fuel pump change I have only put about 200 miles on it.

The SES light came about 1 week ago (22 September 2012). Code reader shows P1131.

Seems to idle and run smoothly. AC on/off doesn’t seem to affect it.

From what I can find P1131 indicates bank 1, upstream O2 sensor, failure to switch.

I think that is passenger side, before the catalytic converter.

Am I right so far?

I visually examined the wiring to the wiring to the sensor … seems to be undamaged.

Given that it idles and seems to run smoothly, would you say the O2 sensor is the likely culprit? Or should I investigate other possibilities first?

Have you cleared the code once? If not get it cleared and see what happens. Or, buy a scan tool and observe that sensor’s output compared to the others and post your observations here.

The ‘possible causes’ for P1130, P1131, and P1132 are many. If you can get to Alldata, the DTC section has the list. The main catagories are electrical system, fuel system, EGR system, induction system, and base engine. What you would be looking for is something that is allowing too much oxygen into the exhaust gases. It could be a vacuum leak, a bad dip stick seal, a leaking exhaust gasket, cracked exhaust manifold, etc. With 216K miles, a check of the integrity of the exhaust system would be in order.

As you suspect, another cause of P1131 (Lack of HO2 sensor switch, sensor indicates lean) is a bad sensor i.e. the sensor can no longer produce a positive voltage. RK’s suggestion to monitor the sensor’s output compared to that of bank 2 may help narrow the diagnosis. If the code returns after a clearing, you might just roll the dice and replace the bank 1 precat HO2 sensor.

Hope this helps.

I might be wrong but the sensor should be about 60$. For all the time messing around with other possibles I usually just start with the sensor. If that is not it then vacuum and injector testing. Depends on how you value time. The O2 sensor can also be checked by a real time scan tool. It will show the actual readings real time under load and idle. Since I have one it is cheap for me. To have a shop do it will start at 60$.

Thanks all. I cleared the code and it hasn’t come back but only driven it 30 miles since then have no clue how long to expect it would take before it would come on again if bad sensor.

I am investigating scanners and software. I’m curious but not planning to become a mechanic so spending a bundle is out of the question… so I’m thinking one of those cheap USB to laptop interfaces … and ProScan software ( … any recommendations along those lines?