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History Sep P0155 (O2 Sensor Heater Circuit Bank 2 Sensor 1) P0135 (O2 Sensor Heater Circuit Bank 1 Sensor 1) P0151 (O2 Sensor Low Volt Bank 2 Sensor 1) - Lazy man repair; just changed them out to see if it cleared.
B2647 (Ambient Light Sensor Circuit Low) - Didn't activate warning light but was stored. No longer stored. Didn't even notice until I was pulling history today.
Nov P0171/P0174 - System Too Lean - Smoke test revealed unmetered air via rusted hole in oil dipstick tube. Replaced tube.
Mar P0151 (O2 Sensor Low Volt Bank 2 Sensor 1)
I didn't drive it between Nov and Mar as it took awhile to get the old dipstick tube out and repair (also replaced some rusty brake line that looked ready to crack).
A member that shows up with codes and freeze frame data. I like this guy already.
First, always show the STFT and LTFT for a given bank because we always add them together.
Your bank 1 fuel trims look good and your bank 2 fuel trims are terrible. You also have a persistent code for the bank 2 O2 sensor. Only one bank has a perceived air/fuel problem so you likely don't have an issue with things common to both banks like fuel pump, MAF sensor, global vacuum leak, etc. Instead, there is an issue specific to bank 2 O2 sensor or its wiring/power, specific fuel injectors, mechanical issue on that side, etc.
Because of the fuel trims and O2 sensor code for bank 2 the first thing to look at is the O2 sensor wiring and power. Do you have a multimeter and know how to use it?
I have multi-meter, Ames DM 600, and know basics (voltage, continuity, resistance).
To confirm, bank 2 sensor 1 is front passenger side - there are 2x white wires, one grey, and one black. I backprobed and connected to test probe. One white showed hot, all others showed ground. Is that right?
Bank 2 is the passenger side and sensor 1 is in front of the cat. Your harness wiring should be:
Heater circuit:
light green/white - heater high
light green - heater low
Signal wires:
Purple - high signal
Tan - low signal
Either at ignition on or when the truck is started cold 12v power is applied to the two heater wires to warm up the sensor faster. That circuit has to be able to maintain proper voltage under the load of the heating element. one way to test it is with an incandescent test lamp across those two greenish wires with the sensor disconnected. You can try just turning the ignition to on and if that does not work, start the truck. If that is ok then the next step are the signal wires. The PCM applies a 0.45V bias voltage on those two wires and the when the O2 sensor becomes active after it warms up it switches that voltage up and down between around 0.15V and 0.85V at a switching speed of around 1 Hz at idle with around a 150ms rise and fall time. So at key on you should see around a half a volt across the two sensor wires.
That said, you are getting a switching signal from the B2S1 sensor in your graphs so the wiring is probably OK but you should measure the bias voltage while you are there. Another check if we get off in the weeds on this is the continuity of those two wires back to the PCM but lets hold off on that. That sensor does look more sluggish than the other bank, did you say that they are all new? Also your post cat sensor graph has problems. It should slowly float around somewhere between 0.5 and 0.7 volts. Was the truck fully warmed up when you graphed that sensor? The cat has to be fully functioning.
I removed sensor and tested for continuity between two same color wires that go to green wires and it was a good.
I have a test probe that you hook up to + and - posts and it lights up red for hot and green for ground. One of the green wires was red and the other three were green. Not sure if lower voltage shows green or if I am not doing it correctly.
I ran the car until 220 degrees and then took more readings.
There is no value in testing continuity on a powered circuit. Those two heater wires from the pcm need to be able to supply 12v with a load simulating the heater element. Marginal wiring will often read 12v with no load but as soon as current starts flowing the voltage drops significantly. Do you have an incandescent test light?
Continuity has its place but not when testing one end of a powered circuit. One place where you would use continuity testing is say you were getting no O2 sensor signal at the PCM. You would disconnect both ends of the signal wire and then test that open wire for continuity and then shorts to power and ground.
Once again, a proper test of the heater circuit is that it can supply enough power to run the heating element properly. A digital test light is a good choice for some testing, especially where the PCM is involved on a low current circuit but not here. The reason why an incandescent test light has its place is for testing like this. The bulb draws a couple of watts so when you test across the two green heater wires from the open harness then you know the circuit is working if you get full brightness on the test bulb. Some people wire up a set of bulbs with different wattages to do load testing like this.
Yes you will eventually need to test the post cat sensor as well. In the absence of full testing of all the circuits you can swap sensors and see if the problem follows to rule out the sensors as the source of the problem.
I have a few minutes to give you an overview of your problem to be used as a guide to help us get this resolved.
You have a unique problem in that your fuel trims are way out of bounds but only on bank 2. Those high trims mean that the engine has commanded what it thinks is the right amount of fuel given all the sensor readings and that's usually pretty close but once you go into closed loop fuel control the final say on fuel injector pulse width are the O2 sensors. They only care about one thing - minimum emissions and they accomplish this by keeping the air fuel mixture as close to "stoich" as possible, a 14:1 ratio. The only time that the O2 sensors do not control fuel injector pulse width is when the engine is cold and in open loop or you floor the gas pedal and go into full acceleration mode. When the O2 sensors make that final determination then the actual injector pulse width is compared to the initial theoretical calculation based on the PCM factory look up table values and the difference is fuel trim. You always add ST and LT together for a given bank and when that number gets big enough, something is wrong. The question is what?
Your bank 2 trims are large and positive which means that the O2 sensor on that bank is adding fuel to compensate for perceived lean condition. I say perceived because if the sensor, its wiring or the PCM has failed the mixture may not have been lean. That why we test the O2 sensor and its circuit to make sure that it is working properly so that we don't end up chasing ghosts. If the O2 sensor circuit is functioning properly then there there is either unmetered air (after the MAF sensor) in that bank or the commended fuel is not getting into the cylinders (fuel injector(s) on bank 2 or their wiring/PCM. If we get here then we will need to check:
Fuel injector output/control on bank 2
Compression on bank 2
Exhaust leaks on bank 2
I'll stay with you as long as you want/need, but we will need to do proper analysis
And yes an incandescent test light is an inexpensive "scope on a rope". For testing that does not need the circuit loaded, keep using your led test light especially around the pcm, you dont want to blow out a driver in the PCM.
03-18-2022, 05:45 PM
P0151 (latest)
