Could use some help, My 02' F150 4.6l is running like crap, especially at low RPM's especially at Idle. Its throwing codes P1131/1151--lack of HO2S-21 Switch, Sensor Indicates Lean and P0155/0156--O2 Sensor Circuit Malfunction. Ive already changed the upstream O2S, reset the computer, checked for obvious vacuum leaks and ran new gas through her. I'm up for suggestions at this point. Thanks!!

 

DTCs

P0155 - HO2S21 Heater Malfunction, Bank 2
P0156 - HO2S22 No activity Bank 2

P1131 - Lack of Switching - Sensor Indicates Lean, Bank 1
P1151 - Lack of Switching - Sensor Indicates Lean, Bank 2
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P0155 = HO2S HEATER OPERATION

The HO2S heaters are tested for both Voltage and Current. A Heater voltage check is carried out by turning the heater on and checking the heater driver pin on the PCM for the correct voltage. This check can run at any time during normal vehicle operation.

The heater circuit current is tested by a separate circuit, and is sampled three times to guard against noise in the circuit. If two of these samples are below a threshold then the HO2S heater is deemed to have degraded. This test is carried out once per drive cycle.
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PO156 = REAR SENSOR FUNCTION

The rear (downstream) HO2S sensors are treated rather differently. The peak and low voltages are also continuously monitored, but if the monitor has not detected a peak or low voltage beyond threshold, then the fuel/air mixture is forced high or low in order to get the sensors to start switching. If this sequence does not 'shock' the rear sensor(s) into switching, then a DTC is recorded.

BTW - Typical voltage thresholds are Rich <0.25 to 0.50 volts and Lean >0.40 to 0.65 volts.
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P1131 &P1151 FRONT SENSOR SIGNAL

The Front sensors are tested continuously for switching during Closed Loop operation provided the Conditions are met. Excessive time between switches, or no switches, indicates a malfunction. Since the lack of switching could be caused by fuel trim shifts as well as a sensor malfunction a stored DTC indicates whether the sensor was always indicating lean or rich when it stopped and if the Fuel Trim was at max.

Where Lack of Switch DTCs are recorded the LT Fuel Trims should be watched closely - if these show well into the negative or positive at idle they could be caused by an air inlet leak or a faulty Fuel Pressure Regulator - meaning that the fuelling has not changed rather than the HO2S not detecting it.

 

You still there? Well, moving on, -

TROUBLESHOOTING

Here's what you can do, plus a little more info. -Leaving out what a dealership with their equipment will do in order to determine the problem. -

Before suspecting the HO2S, the wire connection to the sensor should be checked first. Examine the wires for chafing. Then inspect the connector on the sensor for moisture or damage to the pins. Because the signal voltage is very low (less than 1 volt) the connection is sensitive to damp or poor connection. The heating voltage and current should also be checked and these connections should be clean and bright.
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HEATER CIRCUIT MALFUNCTION

Receiving HO2S Heater DTC codes P0141/P0161 and P0135/P0155 some additional work can be done to pinpoint the cause. In the event that DTCs demonstrate a concern with more than one heater at the same time then the owner must suspect a wiring rather than a sensor fault.

BTW- The heaters are the two white wires. I guess I should also mention, - the gray is a direct PCM ground, not the black. The black is the signal wire.
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CHARACTERISTIC SHIFT DOWN (CSD)

NOTE: In the event that the ceramic element on the HO2S sensor is cracked, raw fuel can contaminate the air reference side of the HO2S. Since the exhaust gas now contains more oxygen than the reference side of the sensor, the HO2S will return a negative value. This effect is called the Characteristic Shift Down, and where it is observed the affected sensor will have to be replaced.

 

Also, when does it run ruff ? Cold idle or Warm idle ?

Write down EXACT idle rpm's and post them.

 

It Runs Rough ALL the Time. It Idles around 900-1000 Cold and 650-730RPM Warm. But if I rev a little, it acts like it starts choking after I let off the gas and I watch RPMs drop around or below 500RPM. Havent got a chance to check anything else yet as Ive been out of town, but I remember it threw a new code for the EGR. Dont remember what code it was, I have it written down at home and will post it soon.

 

I have the same issue with my 2004 4.6 I went to the store for 15 started my truck it popped smoked and started runing rough and sounded like an open exaust leak.I replaced the the exaust manifold gaskets passenger side (Pain in the ***) and now it sounds like the intake manifold is leaking

 

Like I said before, it has to be exact. I can't see it from here.

 

10-4. Is there a good way to get that Number? My code reader and the computer itself wont give me a steady number for Idle. It bounces around pretty good. Timing light to the crank pulley?

 

I have a similar problem. I have 98 F150 with the 4.6 (romeo), it runs rough on warm and cold idle (rpms ~750-800). When going down the road, if I hover around or get below 2000 rpms it starts breaking up and feels like it is misfiring. It will jerk and surge. If I stay above, lets say 2100 rpms, it runs pretty smooth (not perfect but a lot better)?

NOTE: This is a new (reman) motor. My old motor had 280,000 miles on it and I started getting water in the oil and on top of the pistons. It would try to spin over but would stop violently. As far as the misfiring and rough idle, the old motor was doing the same thing.


Everything except for the injectors and the intake manifold are new. The rear cats have been removed with the non-fouler trick done to the downstream O2 sensors. I've checked for a vacuum leak and couldn't find one (on both motors).

 

The computer was reading "excessive flow in the EGR valve". By everything being new, I mean coils, plugs, wires, DPFE sensor, IAC valve, EGR valve, throttle positioning sensor...everything. I replaced everything around throttle body when the old motor was in the truck, except for the plugs and wires those are new for the new motor. I also checked for a vacuum leak (with both motors) and couldn't detect one.


I don't know what else to do!

 

Sorry for hijacking your thread DIVERJAY86. Started my own.

 

Just turned 100k miles truck was running like a champ...... Out of no where a rough idle and flashing cel , backfiring etc.... Codes read P0012 , P2196 , P0174 , P0300-P0304 and P0316 . PLEASE HELP !!!!! Where do I start ????

 

You start by starting your own thread instead of hijacking all the threads in the forum.