Took my 1997 4.6l f-150 into the ford dealership the other day for a rough idle. I had known about the o2 codes prior to this, but never did anything about them. They told me that they just needed to be replaced (I had 3 codes set for o2 sensor heater malfunctions). They wanted an extreme ($300+) amount to replace them, so I decided to do them myself. I ordered genuine motorcraft sensors from amazon, and put them in. I cleared the codes and parked it for the night.

Bank 1 (Pass. Side) sensors went off without a hitch! No codes set for them at all, and have a nice curve on the graph. Bank 2 (Driver Side) sensors are not complying as well as the others. I had codes set for both bank 2 sensors. I used torque to log their voltages through my BT OBD II scanner, and this is the graph it gave (the graph screenshot was taken at idle). The red line is B1S1, Green is B1S2, Blue is B2S1, Purple/pink is B2S2.



After this test I climbed under the truck and unhooked the rear sensor that shows no voltage to check for a cruddy connection. The inside of the connector looked clean so I reattached it. I did not see any damaged wires. After reattaching the sensor, I got back into the truck and cranked it up. I revved the engine to 2000 RPM for a while, and the blue line jumped up to the level that the others were at. The purple/pink stayed at 0 volts.

What is wrong? What tests can I do to find the problem?

 

Swap the downstream sensors and retest. If the sensor is faulty, O2S12 will now be a flatline. If the flatline stays on O2S22, then theirs either a wiring harness or computer fault and you'll need to do some further troubleshooting.

Oh, and just for posterity's sake, write down in big bold capital letters letters that "NEW DOES NOT EQUAL GOOD". Hang the sign in your garage just to remind you not to jump to conclusions.

 

Swapped the sensors today. At first the B1S2 (was B2S2 that showed no voltage) showed no voltage. I revved between 2-3k RPM for a minute or so and then it picked up. B2S2 still shows no voltage and B2S1 still shows less fluctuation than the other 2 before revs (like the first graph I posted, blue line) , but picks up afterwards (as on this graph) .

 

If you leave the sensors in place long enough, the system will set codes for the self diagnostic failures detected.
This narrows the fault depending on what they are.
Your placing to much concentration on wave forms before addressing the codes.
While the wave forms do tell you of the faults, they are not helping you at this point.
What do you have?
Possibilities are;
a. Lazy and /or dead senors from contamination.
b. Faulty wiring harness.
c. Loss of sensor heater circuits.
c. Possible faulty cat converter.
d. More than one fault at the same time causing confusion.
e. Your moving the faults around and causing 'you' confusion.
What are the codes then begin from them to tell you what the diagnostics see.
Good luck.

 

As mentioned..

P0155 - O2 Sensor Heater Circuit (Bank 2 Sensor 1)
P0161 - O2 Sensor Heater Circuit (Bank 2 Sensor 2)
P0401 - EGR Flow Insufficient Detected

 

Do a "suck test" on the EGR valve itself while idling, if the EGR valve is good and the passages aren't plugged, it should stumble and may stall. If it doesn't you need to find the blockage. If it does stumble, it's probably a bad DPFE or associated hoses.

The 4.6 is famous for the EGR passages in the throttle body elbow plugging up.

 

Ok! Whats the problem in servicing for these codes?
Both banks heater circuits are 'open'.
It's the harness wiring or the plugs.
I do not believe is a fuse because the fuse supplies power to other functions you do not have codes set for.
Inspect the harness for being cut or open feeding both sides.
The rear sensors also need heater power. Check them for missing power.
Voltmeter is your friend.
.
The 401 code is a separate fault.
The fault is a flow test failure.
One of a number of tests done on that system.
Test the EGR with vacuum to be sure it can open when the engine is in idle.
If yes and the intake port is not blocked, the engine will idle very rough and may stall.
Then the fault will lie with the DPFE, hoses or the EVR.
.
You don't need a waveform display to repair any of these faults.
All they are doing is confuse you at this point by verifying there is a problem but not the cause.
Good luck.

 

What pins do I need to check on the plug for heater power?
Do I just crawl under the truck and trace the harness from the back forwards?

Thanks for the assistance.

 

I beg of you to use common sense.
Yes the sensors are on the exhaust head pipe each side under the exhaust manifolds.
They have 3 or 4 leads going to them.
One pair is the sensors outputs back to the computer. Those are the responses you saw from the wave forms.
DO NOT use an Ohm meter to test these sensors. They are not resistances but are temperature/ driven voltage generators.
The other is power and ground to the built in heaters.
You may test these for continuity but more important to test for voltage from the fuse with the Ignition key on Run.
.
All these are electrically monitored by the computer for opens, grounds and crosses as this is how the codes are set for each fault.
The rear Ox sensors are under the truck in the middle of the rear Cats with a harnesses feeding to and from the same as the fronts.
All this goes back to the computer and power source.
Some where in the span there is an open or ground outs.
The codes tell you this.

.
The 401 code is a separate issue but 'possibly' could be harness related (if) there is a physical common point where all the wire are in fault.
You have to do the work or let some one else do it.
.
Good luck.

 

An ohmmeter may be used to test the heater circuit (it's in the service manual).

However, a dead heater won't cause an O2 sensor output to flat-line. It will just cause it to have to warm up from exhaust flow only so it will be pretty sluggish until it comes up to temp without the heater.