[99Silv4.3L]

Day-7 Monday
Truck sat over night; fuel dash gauge at 3/8th full.
Started engine, shifted to neutral, A/C & Fan off, 4 incomplete I/Ms

Minute	ECT (F)	IAT (F)	Fuel Syst	Codes	A/C & Fan@4
0	48	43	Open	none	off
4	94	48	Open	none	off
6	113	48	Open	none	off
7	122	48	Open	none	off
8	129	48	Closed	P0161	off

Was expecting a P0141, not a P0161.

So for the computer to evaluate the function of the two O2 sensor heater circuits, it doesn't seem necessary to run an idle test (2).

I had removed/labeled/swapped bank 1 and bank 2 post-cat sensors two days ago, but got the same code today, P0161. This is consistent with sensor heaters testing fine, both with a resistance of 4.9 ohms.

But with key-on, there is battery voltage across the pink & black harness wires at the disconnected harness connector. And there is also battery voltage between the battery post B+ and the inner terminal of O2B at the fuse box in the engine compartment.

There have never been codes related to the other three sensors. Since the wiring diagram shows the 4 sensor heaters sharing a common ground, the ground connection is probably in good condition.

Since the bank 2 precat sensor has always been code-free, the P0161 could be caused by a poor connection in bank 2 postcat sensor heater circuit. There is single fuse for both sensor heaters on bank 2. There is single fuse for both postcat sensors. Somewhere after the fuse the wires must fork, one going to the precat sensor heater and one to the postcat sensor heater. Somewhere after the fuse the wires must fork, one going to the bank 1 postcat sensor heater and one to the bank 2 postcat sensor heater. The fork could be in the harness where the harness, or could be at the fuse box, which is where the wiring diagram shows them forking, but it's just a schematic, not a blueprint. Anyway, the possible poor connection would be somewhere between where the wires fork to the two sensors, and the harness connector for the post-cat sensor.

 

[bowtieguru]

I read the wrong code number when I stated P0155, you are right, should have been P0141.

Mitchell shows 02A fuse feeds the upstream and 02B feeds the downstream, connected together right at the underhood fuse box. Both wires will be crimped in the same terminal.

The ground shows as B2S2 is first in the circuit from the ground on G104 (back of the driver's side head). You should physically look at the eyelet and tug on the wires to make sure one isn't corroded or broken.

Any exhaust leaks?

 

[99Silv4.3L]

Mitchell shows 02A fuse feeds the upstream and 02B feeds the downstream, connected together right at the underhood fuse box. Both wires will be crimped in the same terminal.

Thanks, on closer look at the Haynes/Chilton schematic, it shows what you said. I'll go back later and correct my mistkes in previous posts.

The ground shows as B2S2 is first in the circuit from the ground on G104 (back of the driver's side head). You should physically look at the eyelet and tug on the wires to make sure one isn't corroded or broken.

Thanks, the Haynes/Chilton schematic doesn't identify which/where the ground is, at least not that I can see.

Any exhaust leaks?

No leaks that I can hear. But there is a downstream exhaust leak, at the joint where the muffler pipe connects to the Y-Pipe. The location from that joint to the P0161 sensor measures 13 inches. I only know that there is a leak at that joint because it drips water, so I was thinking the leak is minor, would not matter, and was going to take care of it after the DEQ inspoection. Let me know if you think the exhaust leak is a likely cause.

When I had the y-pipe off 6 or so weeks ago, it didn't look like that joint has a replaceable gasket. Does it? (V6 2WD Ext Cab Manual Trans). Short story is that when I had the y-pipe off due to a cracked weld/flange on the y-pipe where it bolts to the driver's side bank1 exhaust manifold. I replaced the two gaskets where the y-pipe bolts with the exhaust manifolds.
=======
Day-7 cont Monday
I'm working on some voltage-drop tests at the moment in hopes of identifying a poor connection. I've never run a voltage-drop test, but have heard about them. So I rewatched Schrodingers video here:

I draped a ten foot 14 gauge extension cord from B+ to the passenger side. It is a cord I use regularly without issues with power tools. I pinch-clamped one of the cord's flat terminals at the B+ post.

I jammed a T-pin in the harness connector for postcat sensor to back probe the pink wire in the harness. With O2 sensor connected to the harness and the key on, the voltage-drop was only 0.2V. I believe this means that the section of the circuit from the battery, to the ignition switch, to the fuse box, to harness connector is fine relative to the amount of current drawn by heater.

I jammed another T-pin into the back of O2 sensor pigtail connector at the wire corresponding to ground (black wire on the harness. With sensor connected and key-off, the voltage-drop to the frame was 0.00V. With key-on, the voltage-drop increased a fraction but still less than 0.1V. I believe this means that the section of the circuit from the sensor pigtail, through the connector, through the harness, to the ground bolt, to the chassis is fine relative to the amount of current drawn by heater.

In hind sight I should have back probed the pigtail for both voltage-drop tests.

 

[99Silv4.3L]

Yesterday, Monday, I finished up by moving the pink wire T-pin from the harness side of the connection to the pigtail side so that the voltage-drop measurement would include the connection itself. The key-on voltage-drop increased by about 1/2 volt, so no real change.

So my conclusion was that the heaters of both sensors in the post-cat bungs were fine, and that all the wiring and connections in the post-cat circuits was fine. I thought the exhaust leak might be a possible cause of the P0161, but unlikely. The Y-pipe, cats, intermediate pipe, muffler, and tail pipe are the factory originals and are 99.9% rust free. The y-pipe/manifold joints have new gaskets. The only leak I'm aware of is small, located at the Y and intermediate pipe connection. I was planning on fixing that as the next step in solving the P0161, but didn't get around to it yesterday. So last night I erased the codes so that for next day's (today's) cold start, I could repeat the tests I had run yesterday morning.

==============
Day-8 Tuesday
I'm dejected to have to say that after the cold-start P0161 yesterday, this morning the cold-start produced a P0141.
Truck sat overnight with the dash fuel gauge showing 3/8ths full.
Started engine, shifted in neutral, A/C and Fan off.

Minute	ECT (F)	IAT (F)	Fuel Sys	Codes	A/C & Fan
0	43	43	Open	none	off
7	118	48	Open	none	off
8	130	48	Closed	none	off
12	160	48		none	off
13	167	48		P0141	off
15	176	48		P0141	ON
22				P0141	off
26				P0141

I'm at loss for any explanation what so ever. I've been taking meticulous notes on a clip board. I'm 99.9% certain that yesterday's code was P0161, and today's is P0141.

They are AC Delcos. I'd have to find my notes from several years ago to know if I replaced them then. I've never had to do work to pass DEQ. If I did replace them, it would have been in June of that year (DEQ comes up in Oct) when I was doing a ton of maintence prior to a long road trip. If I didn't replace them at that time, then they are factory originals.

Since time is running out for DEQ inspection, I'm ordering two new post-cat sensors today in case I end up wanting to replace them. But I really do not think the current ones are bad.

 

[99Silv4.3L]

Day-8 cont Tuesday
Drove the truck front end up onto ramps.

With key-on, and using yesterday's T-pins still back probed in the pigtail connector in sockets C and D, I measured the voltage across the T-pins. Voltage-drop, as expected was close to battery voltage, 11.81V. This on the passenger side which has the swapped in O2 sensor originally installed on the driver's side.

I grabbed two more T-pins and back-probed the driver's side sensor pigtail, finding 11.77V with key-on. With key-off, the resistance across the T-pins to be 2.5 ohms, which is what one would expect since the resistance path is for the two heaters in parallel, since the the two sensor heaters are connected via their common hot wires.

All the electrical test seem consistent. The circuit wiring and various connection for the post-cat sensors on both banks match and are fine even under load. And the two heaters match and fine. Given ohms law, each heater draws heaters draws about 2.4 amps, so the 15 amp fuse carries about 5 amps.

I look online again for a gasket for the leaking Y-pipe / intermediate-pipe connection, but couldn't find any indication that the joint is designed for one. The two flanges there have an integral, non-replaceable donut type configuration similar to the replaceable donut on at passenger side Y-pipe / exhaust-manifold connection.

So to address the leak, I unbolted the leaking joint, wiped down the mating surfaces, applied a bead of Permatex silicone that they market as a sensor-safe exhaust sealant, then rebolted the joint.

There is easy access to the two y-pipe / exhaust-manifold joints. Since the engine and exhaust had cooled, I started the engine and felt around those two joints with my fingers but didn't feel any puffs/currents of warm air, or any puffs at all.

 

[99Silv4.3L]

Day-9 Wednesday
Truck sat overnight with the dash fuel gauge showing 3/8ths full.
Was up at 2:30 am, went outside to try to sneak in an extra early cold start.
Started engine, shifted in neutral, A/C and Fan off.
ECT IAT were 57F and 48F, which barely meets the "within 11F" cold-start criteria

Minute	ECT (F)	IAT (F)	Fuel Sys	Codes	A/C & Fan
0	57	48	Open	none	off
5	108	48	Open	none	off
6	118		Open	none	off
7	127		Open	none	off
8	135	52	Closed	none	off
9	145	52		none	off
10	156	52		none	off
11	165			P0141	off
15				P0141	off

Turned off engine. Erased codes.

Truck then sat for 8 hours until I went back out at 11am for another cold start.
Dash fuel gauge showing 3/8ths full.
Started engine, shifted in neutral, A/C and Fan off.
ECT IAT were again 57F and 48F, which barely meets the "within 11F" cold-start criteria.

Minute	ECT (F)	IAT (F)	Fuel Sys	Codes	A/C & Fan
0	57	48	Open	none	off
3	97	52	Open	none	off
5	118	52	Open	none	off
6	130	54	Open	none	off
7	138	54	Closed	none	off
8				none	off
9	154	54		P0141	off
14	187	54		P0141	off

Turned off engine. Erased codes

 

[99Silv4.3L]

Found this ground distribution diagram for O2 sensors in a 9 year old photo collection from a library book:

 

[bowtieguru]

Why are you still chasing the heater circuit? There is no problem with it.

The problem is a lazy O2 sensor, taking too long to start switching. You moved the sensor and the code moved so replace it!

 

[99Silv4.3L]

I don't think it's that certain, but yep, could very well be that half of the sensor. Or something else. I doubt it's the small downstream exhaust leak (fixed yesterday), or the G104/G114 ground (since it's shared by the oil level circuit and the two precat sensors, which haven't thrown any codes).

One test I haven't done is monitor the voltage drop across the heater during the 8 minutes or so of idling following a cold start. But given the momentary measurements that I've taken of the key-on voltage-drops across the heater elements, I doubt it's the heater circuitry.

Another test I have not done is back-probe monitor the O2 sensor signal. I don't have an appropriate tool for that, but think they can be had for under $100, such as the PS100 by Autel.

I've several apple boxes full of nearly all the old parts I've pulled from the truck. I rummaged through them today, but found only two oxygen sensors, and they were precat, replaced precautionarily a few years ago when I was preping for a long road trip. So the postcat O2 sensors that are currently on the truck are factory origianl, 21 years old with nearly 300k miles on them. They are AC Delco AFS 106. As I wrote above, I've two AC Delco AFS 106's on order.

 

[99Silv4.3L]

Day-10 Thursday
Truck then sat overnight. Dash fuel gauge showing 3/8ths full.
Started engine, shifted in neutral, A/C and Fan off for the duration below.

I found out that the Actron CP9580 allows one to live-graph one data item at a time, so I took some pics of the postcat O2 sensor signals during this mornings trial. I'm not sure if this is the raw voltage data streaming from the sensor, though I doubt it, or if it is what the computer is reporting. Anyway, it includes whatever filtering is coming from the wiring.

The main difference I saw between the P0141 sensor signal and the other sensor signal is that the P0141 sensor signal has a visible amount of high frequency noise, though it might not be too obvious in the cell-phone photos due to blurring of a slow shutter speed. The amount of noise in the P0141 sensor signal decreased somewhat as the minutes passed. Also, it looks like the sensor signals are analog, so I'm not sure what is meant by switching in "too long to start switching".

Minute	Engine	ECT (F)	IAT (F)	Fuel Sys	Codes	O2S12	O2S22
0	start	54	48	Open	none
4
6	idle	122	54	Open	none
7	idle	135	54	Closed	none
8	idle				none
9	idle	165	54		P0141
10
14	off
15	erased codes
16	start	183	57		none
17	off	189	57		none

Turned off engine. Erased codes

 

[99Silv4.3L]

Understanding & Live Graphing of the Rear O2 Sensor: OBD4Everyone Ep.19

 

[99Silv4.3L]

Day-10 cont Thursday
The pair of new sensors that I ordered (ACDelco AFS106) arrived last night. Unfortunately, or not, they are not ACDelco AFS's 106s. My truck has the factory original sensors,, and they are stamped ACDelco AFS106. The ones that arrived are GM Genuine 19355306, and their heater's have 3 times the resistance, 17 ohms compared to 5ohms. With a resistance being 3 greater, the current will be 1/3rd, or 12/17=0.7 amps. Given the reduced current, the resistive heating will be reduced to 1/9th. The sensor looks completely redesigned, so maybe they reduced the thermal mass accordingly.
Some other aspects match, such as length of the pigtail, and a single divider in the connector.

Anyway, drove the front end up on ramps, pulled the P0141 sensor and installed the new one. The engine had not cooled enough to qualify as a cold-start, but I let it idle into closed loop mode on the off chance the computer would give it a pass.

Minute	ECT (F)	IAT (F)	Fuel Sys	Codes	A/C & Fan
0	91	64	Open	none	off
4	129	64	Open	none	off
5	135	64	Closed	none	off
14				none	off

So, no codes and all 5 I/Ms incomplete: cat / evap / egr / O2 Mon / O2 Htr

Dash fuel gauge was getting close to 1/4, so drove to the station to add a few gallons.

 

[shakenfake]

So are you done yet?

 

[99Silv4.3L]

Day-11 Friday
Truck sat overnight with the dash fuel gauge 1/2 full.
Started engine, shifted in neutral, A/C and Fan off.
ECT IAT were 59F and 48F, which either meets or misses the "within 11F" cold-start criteria

Minute	ECT (F)	IAT (F)	Fuel Sys	Codes	I/Ms	A/C & Fan
0	59	48	Open	none	5 inc	off
7	122	54	Open	none		off
8	127	54	Open	none		off
9	133	54	Closed	none		off
10	138	54		none		off
11	144	54		none	O2Htr OK; 4 inc	off
19	167	54		none	O2Htr OK; 4 inc	off

Took it for a drive. The other O2 I/M completed OK, at which point there were no codes and 3 incomplete I/Ms: cat/evap/egr

Did the (345) drive cycle test, then the (678), then turned around and headed home driving regularly. Still no codes and 3 incompletes.

 

[99Silv4.3L]

So are you done yet?

Ha, ha. No, the systems that incorporate the O2 sensors, they need to complete.

 

[99Silv4.3L]

Day-11 cont Friday
Sat for a couple hours.
Took it out on a one-stop errand, 40 minute, surface streets.
Sat for an hour.
Took it out on some errands. Firstly, 35 min, mostly highway at 55mph. Sat for a half hour. Then 3 more stops. Then 45 min, mostly highway, mostly 30-40 mph.
Three I/Ms have not completed: cat/evap/egr.
Both I/Ms for the O2 sensors are completed, OK'd.
No codes.

 

[99Silv4.3L]

Day-12 Saturday
Today's entire 1.5 hour session started and ended with:

• no codes
• I/Ms OK: O2 Mon and O2 Htr
• I/Ms inc: cat/evap/egr

Truck sat overnight with the dash fuel gauge 1/2+ full.
Started engine, shifted in neutral, A/C and Fan off for the idle, fan/heat on for the most of the drive.

Minute	ECT (F)	IAT (F)	Fuel Sys
0	57	48	Open
7	127	52	Open
8	135	52	Closed
11	162	52

Took it for a drive.
Highway speeds were 55mph give or take.

Minute	What
13	started out
21	pulled onto Interstate
26	coasted down to 20mph
29	began (345) cycle
34	began (678) cycle
41	turned around
56	exited highway
65	engine off
72	engine on
103	home

 

[99Silv4.3L]

Day-12 cont Saturday
Weekend trip

Hour:Minute	Approx Miles	Elevation	What	codes	I/Ms: inc	I/Ms: OK
0	0	0 ft	started out	none	cat/evap/egr	5
11			pulled onto Interstate
24			exited, stopped for gas to 5/8ths full
28			back on road
40			onto divided highway
1:21	50	2000 ft	stopped
1:39			back on highway
2:17	70	5000 ft	stopped
4:02			back on highway		cat/evap/egr	5
?	?	?	on highway		cat/evap	6
4:30	90	2000 ft	home	none	cat/evap	6

So, another I/M, EGR, finally went from inc to OK, possibly due to multiple prolonged stretches of in-gear coasting at 45-55 mph during the 20 mile descent from 5000 ft to 2000 ft, which involved some intermediate ups and downs, so probably 4000 ft total descent. The Actron's page for 'State OBD' doesn't seem to update live, so while it was hooked up while driving, it's unknown exactly when during the final leg the EGR I/M completed.

 

[99Silv4.3L]

Day-13 Sunday
Weekend trip
Truck sat overnight with the dash fuel gauge 1/2+ full.

Hour:Minute	Approx Miles	Elevation	What	codes	I/Ms: inc	I/Ms: OK
0	0	2000 ft	started; on highway	none	cat/evap	6
41	17	4000	stopped
2:50			back on highway
3:11			stopped for gas to 5/8ths full
3:28	40	1500 ft	stopped
3:37			back on highway
3:47	45	2000 ft	stopped
7:06			back on highway
8:21	94		home	none	cat/evap	6

So, even after 3 cold starts, despite no codes, two (345) cycles, two (678) cycles, and additional normal hwy/road driving bringing the total over 250 miles, neither the cat nor the evap I/Ms have completed.

 

[shakenfake]

Yeah the evap I/Ms are extremely dumb to get to complete. You need to have half a tank I believe for it to complete.

Who cares about if they complete you got no codes