I have a 1996 F-150 4x4 with the 5.0 that has 37,000 miles on it and is in stock condition. The truck was purchased new by my father who passed and was given to me. The check engine light has recently come on and is showing 3 OBD 2 codes of 135, 141 and 155 which point to the oxygen sensors. Seems strange to me that all 3 oxygen sensors would go bad at the same time. I am checking easy to hardest. Started with the fuse then replaced the air filter, was going to clean the mass airflow sensor but my factory Ford Manual says not recommended to clean. What else should I check or should I just remove and replace the 3 oxygen sensors and see what happens.

Thanks

 

Could be an ECU issue. It definitely seems unlikely that all three sensors would fail at the same time, and in the same way. Pins 93, 94, and 95 should be the Heater monitor wires on the ECU.

 

1996 you can monitor those HEGO pids and watch them switch
You can see how long it takes them to start switching from cold start (the reason for the heaters anyway)
I sure would clear the codes and retest at least a few times (looking for those same codes to return) before replacing anything
When the heater burns out in the HEGO you have only one fix, to repolace the HEGO, yes uncommon for all to fail at once
Check the grounds in the RF kick panel

 

Thanks for your reply and input.

 

You damn sure can clean the MAF (the hotwire in particular)
That sensor is commonly known as a hotwire sensor where there is a toaster type grid wire (2 actually now days)
Those wires get dirty and need to be cleaned periodically, also spiders find their way into the sensor port if the vehicle sits
You remove the MAF, remove the plate with the tamper proof Torx screws and clean the wires
If you've got some ***** you bend each wire back and forth slightly, that removes any crust / varnish
You can check the maf sensor pid against reference tables, pounds per hour or a voltage number

 

It the ECM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135, P0141 and P0155.
I would start by troubleshooting any warm up issues that you may have. Most engines have at least two coolant and/or engine temperature sensors and, in general, one goes to the ECM and the other goes to your gauges.
Bad thermostat?

 

Could a missing washer on the bank 1 sensor 2 oxygen sensor cause my PO135, PO141 and PO155 codes? Seems it rusted away. I have 12 volts to the sensor and 3 .9 ohms resistance measured at the two white wires.

 

Still trying to get those 155/135/141 codes ironed out. No luck yet. Truck idles good, runs good. O2 sensors seem to check out with battery voltage and 3.9 ohms except the Bank 1 sensor 2 has a missing crush washer that seems to have rusted away, Have been following the Ford Powertrain Control/Emission Diagnosis Manual Fuel Control Pinpoint Tests and so far all checks out. Maybe I will just try and replace all 3 O2 sensors and see what happens. Maybe I will get lucky. Any input on brand of O2 sensors. Rock Auto has both Bosch and Walker Brands. The original O2 sensors are Bosch with a Ford part number but Ford parts.com says they are obsolete. I tried to get a crush washer at 5 different places and no one has any.

 

Are you having any problems with the engine warming up? Use an Infar red temperature detector and see what your actual temperature reads. Shine it at the area near the thermostat after warm up is complete.

 

Checked G200 behind the bottom right kick panel. inspected, cleaned and reinstalled. In fact, I checked, cleaned and tightened all the grounds.