P0420 / P0157 – 05 Chevy Express 1500 V6 4.3L

[Rob]

Getting P0420 / P0157 code.

2005 Chevy Express 1500 V6 4.3L
Cats replaced 30k miles ago (160k on vehicle )
New NGK Iridium IX plugs
Oil serviced every 2500 miles
K/N air filter cleaned every 10k

Right side downstream o2 seems bad ( low voltage ) but I don’t know what to make of left side downstream o2 sensor. I don’t have a laser temp sensor to check before and after cat tamps.

Here is a quick screen capture from my phone running Torque at ~2500rpm and idle.

Topic

[Billy]

I wouldn’t worry about the bank 1 downstream sensor till you’ve dealt with the bank 2 downstream sensor, which by all indications is dead or has bad wiring.

[Rob]

Thanks, I will update once the new Denso sensor comes in.

[Rob]

I have replaced the bank 2 downstream sensor and instead of what i was getting ( .1-.2v ) now I am getting .0v on the tool
Unplugged the bank 2 downstream sensor and now I am showing .4v constant on the tool
Replaced bank 1 downstream and nothing changed, same voltage on the tool
Unplugged bank 1 downstream and it is reading .4v constant on the tool

With both bank 1 and bank 2 downstream sensors unplugged, I check for shortages ( none found ) and voltages with my DMM.

Bank 1 downstream while car is on running showing 13.9v ( same side plug ) and 12v ( across from each other )
Bank 2 downstream while car is on running showing 13.9v ( same side plug ) and 4.4v ( across from each other )

None of the plugs are corroded or look burnt, traced the wires as much as I could see on both downstream sensors and everything looked OK.

Both sensors were replaced with brand new Denso sensors.

Both fuses for O2 sensors were OK.

Any suggestions?

[James]

Are those traditional O2 sensors or A/F ruel ratio sensors (Wideband O2.)

What do your fuel trims look like? Are the up stream O2 sensors switching or staying constant at 0.1 v?

[Rob]

[quote=”jjohnson1″ post=184224]Are those traditional O2 sensors or A/F ruel ratio sensors (Wideband O2.)

What do your fuel trims look like? Are the up stream O2 sensors switching or staying constant at 0.1 v?[/quote]

I am not sure if they are wideband sensors.

both bank 1 and 2 up stream sensors are switching fine like before ( refer to first post video ).

I have on my Torque program the option for:

Fuel Trim Bank 1 Long Term
Fuel Trim Bank 1 sensor 1
Fuel Trim Bank 1 sensor 2

Fuel Trim Bank 1 Short Term
Fuel Trim Bank 2 Long Term
Fuel Trim Bank 2 Sensor 1

no date for Fuel Trim Bank 2 Sensor 2

I can put all 6 of those on one screen and screen capture, what would like to see? idle, certain constant rpm?

[Rob]

I have one more option

Fuel Trim Bank 2 Short Term

[Rob]

Ran the test again with new Denso downstream sensors.
~2,300rpm up 2:25 in the video then idle until the end of the video

what you are looking at in the video

Long Term Fuel Trim Bank 1 | Long Term Fuel Trim Bank 2

Fuel Trim Bank 1 Sensor 1 | Fuel Trim Bank 2 Sensor 1

Short Term Fuel Trim Bank 1 | Long Term Fuel Trim Bank 2

I was mistaking and there is no Sensor 2 for either bank or at least it is not showing for me.

[James]

As you know, you are stuck lean on bank 2 sensor 2. Possible your new O2 is bad

Or

You need wiring diagram to check o2 sensor wiring integrity

Fuel trims are lean on both banks as well, more so with acceleration. Figure out o2 sensor and can re address that

[Rob]

[quote=”jjohnson1″ post=184247]As you know, you are stuck lean on bank 2 sensor 2. Possible your new O2 is bad

Or

You need wiring diagram to check o2 sensor wiring integrity

Fuel trims are lean on both banks as well, more so with acceleration. Figure out o2 sensor and can re address that[/quote]

Hmm, I will see if I can pick up another o2 sensor.

On a side note, the video started with me already revved up and holding at ~2,300rpm until around 2:25 mark in the video where i step off the accelerator and let it idle until the end of the video. There shouldn’t be any acceleration done in the video besides the 100 or so rpm here and there.

I can do an acceleration test tomorrow and post that.

Will try to retrace the o2 wiring more thoroughly tomorrow if weather permits.

[James]

LT Fuel trims were near +17 both banks at 2300 RPM. Both Decreased when going to idle. Best of luck on O2. Stuck at zero. Could introduce propane, snap throttle etc but looked pretty stuck at zero. ensure not grounding out somewhere as well.

[Rob]

[quote=”jjohnson1″ post=184271]LT Fuel trims were near +17 both banks at 2300 RPM. Both Decreased when going to idle. Best of luck on O2. Stuck at zero. Could introduce propane, snap throttle etc but looked pretty stuck at zero. ensure not grounding out somewhere as well.[/quote]

Thanks for the input.

[cj1]

bbbind.com has schematic so you can identify circuit/pins verify heater circuit from sensor ref circuit.
Regarding 4.4v when measuring across heater pins, measure again from battery side of connector to car body ground.
If voltage is normal then suspect high resistance in ground side of heater going to low control pin at PCM.
If v still 4.4v then suspect high resistance in positive side circuit.

[Rob]

I haven’t checked the voltage with the body ground but I put half a tank of 93 and drove 180 miles with the new downstream sensors and no codes so far. Everything is showing ready and completed but the bank 2 downstream sensor still behaves the same with occasional jump from .1v to .7v when idling.

[Author]

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