My 2001 F150 5.4L 2WD is being very stubborn. A little background. I purchased the truck new in November 2000 with 9 miles on the OD. With the exception of the cruise control recall work, no one has turned a bolt on this truck other than me. The wiring is in as new condition and has never been molested in any way. Mechanically the only modification from stock is a K&N air intake system. All emission sensors were properly installed in the intake system per K&N directions. My F150 has approximately 90,000 miles and has never been involved in any kind of collision or any other physical damage.
About 2 years ago the CEL illuminated. I read the codes and got a reading of P0122 “Throttle Position Sensor circuit low input”. The engine had been surging slightly during warm up at cruising speeds so ok bought a name-brand replacement TPS, installed with battery disconnected, went through Fords stated factory idle “relearning” process and figured good to go. Two months and 2,000 miles later I park, put the truck in park and the engine revs to 2,200 rpms. Took it home, read the codes -- P0122. So OK maybe my truck doesn’t like anything but factory parts so I get a Motorcraft TPS, install as per above—good to go right—well for a while. Checked codes about a month later—all clear including P1000.
CEL comes back 500 miles later. I read the codes and so now P0122 is back and I also have P0135 “Upstream heated O2 sensor heater circuit fault (bank1, sens1). I’m still sweating bullets over TPS but in the meantime I can replace the O2 sensor. Bought a NTK replacement O2 sensor fresh from warehouse, installed on passenger side in front of cat—good to go right—NO, both codes back along with some new ones. I check the voltage by using old O2 sensor to insure voltage flowing and connector good. Power is there. Checked ohm reading on heater circuit in new sensor, shows low ohm reading which I believe is proper reading.
So guys and girls any creative ideas. I admit I am old school, if this were my 67 mustang the problem would have been diagnosed by ear and fixed and done. The electronic systems are a pain but hey I adapt.
The codes as of today are: P0122 as noted above. P0135 as noted above. P1125 Throttle Pos Sens A Interm and P1132 Lack Of HO2S Switch – Sens Indicates Rich.
My frustration comes from knowing if I take it to a dealer they are going to throw parts at it, just like I have, until I finally give up.
Questions:
Do dealers or good independents have test equipment to get behind these codes other than the sensors themselves?
Can a battery that is acting perfectly (voltage dash gauge reading normal) normal be failing causing these codes that can’t be fixed.
Are defective new emission parts common? Any suggestions and answers to my questions will be greatly appreciated.

 

I would say new parts are rarely defective. It would be unusual to get a bad o2 out of the box. Also i would say that the o2 code is caused by something other than a bad o2. Low input I believe is that say at Idle, your TPS should return (just for example) like .5 volts, and it is returning 0. I believe since you have all ready replaced the sensor twice, I would trace your wire back to the PCM and take the voltage reading by backprobing the sig return wire from your TPS at the PCM. If you see that your voltage is below the threshold at the PCM and, is normal at the TPS, then you know you have a break in the wire somewhere. Say your TPS is off and you are getting too much gas, then bang, there's your o2 code. I'm sure someone on here will have the correct voltage values for the TPS on your truck.

Good luck! and welcome to FTE!

 

I would also add that a grounding issue, especially to the computer, can cause a broad array of codes, so don't rule out that possibility.

Your problems may be worsened by the fact that you have the K&N filter. You see, the computer determined how much fuel the engine should need by interpreting the signals from a variety of sensors, but two of the more important ones are the MAF sensor and the TPS. K&N filters have a long history of fouling the MAF element with both oil and dirt. This prevents an accurate reading, which the computer interprets as less air going into the engine.

However, neither of these sensors has any bearing on the O2 sensor. The O2 sensor is part of a separate system which alters the fuel trim. One possibility regarding the O2 sensor code repeating, did you replace both upstream sensors? Those should be replaced every 80,000 miles whether there are codes or not.

As far as professional diagnostics, they use scanners to see whats going on. A code reader is just that, it retrieves the codes from the vehicles computer, but a scanner on the other hand, can look at live data from the sensors, and see what the computer is seeing. A knowledgeable technician that knows what to look for can spot erratic readings and isolate their cause. It would probably be less expensive than throwing more parts at the problem.

 

Yeah good catch Bear River, I totally forgot about the ole K&N on it. Its actually amazing how many MAF problems are caused by them. I remember going to a college visit back in high school where an owner of a sucessful independant repair facility made it a point to hold up a mass air flow sensor and a oil wetted air filter ( I guess I shouldnt just single out K&N) and explain how they get ruined because of the oil on the filter. I think it would be in your best interest to change out your filter element for a dry flow element.

You can also try cleaning your MAF using some cleaner that you can purchase at parts stores. I know most shops just use brake cleaner. Incorrect MAF readings can cause an o2 code. However since you have a TPS code I would address that first.

 

The part mentioned in the code description is often not the cause. What you have is a generic OBDII code for the TPS telling you that it isn't working correctly. The P1125 is a more specific code that is defined by the manufacturer telling you that you have an intermittent failure of the 'A' ckt, which is a fancy way of saying that one of the wires going to the TPS isn't making a consistent circuit for whatever reason. The 135 and 1132 are also similarly related. If it is always reading rich there probably isn't a problem with the sensor, if there was it more than likely wouldn't be generating voltage.