Hey all,
I’ve been having some sort of error codes with o2 sensors for a while and still cant figure out

most recently Im getting these p0174 p0171 p1171 p0150

i recently changed all 4 O2 sensors ( was getting codes before that too)

Had muffler work done for some leaks

replaced all spark plugs

cleaned MAF, iACv, and throttle

truck runs smoother now but still getting those codes


I plan on checking for vacuum and exhaust leaks again and possibly replacing the MAF. Any other suggestions?

 

Suggest posting exact code meanings from RAVE manual, most of us do not memorize the code meanings.

 

Yep, sorry I forgot about that. Here are the descriptions


- P0171: System too lean (bank 1)
- P0174: System too lean (bank 2)
- P1171: System too lean (bank 1)
- P0150: 02 Sensor Circuit Malfunction (Bank 2 Sensor 1) Front sensor RH bank stoichiometric ratio outside operating band.

 

Your truck has a vacuum leak affecting both cylinder banks. A smoke test may help you locate the source of the leak. In the meantime, examine the intake tube after the MAF and to the upper intake, and also examine the fittings for the PCV and brake servo vacuum pipe on the other side of the intake.

 

Two possibilities, either your truck is actually running lean or it thinks its running lean due to failed oxygen sensors. If it is not the oxygen sensors they will output close to .8-9 volts at stone cold startup for few seconds before they go back to .1 v. If the 02s are bad they will not do that. Best to watch them with an analog chart like available on Torque app using an Elm327 bluetooth obd2.

 

Thank you for the insights. I will plan on monitoring the sensor output voltages along with MAF readings at startup and soon after as well. In parallel will be doing a smoke test too.

as far as I can tell up until now I’ve always seen my upstream sensors around 0.3v to 0.49v and downstream o2 at 0.8v to 0.99v. Does this tell anything?

 

You really need to be able to see them on an analog graph/chart to tell anything. If you told me they never move then maybe that tells you something but those numbers could be normal if you are missing the high cycle part of the phase.

 

The downstream sensors have nothing to do with engine management. Their sole purpose is to monitor the effectiveness of the catalytic converters.

The upstream sensor output voltage should bounce back and forth above and below 0.445 volts, as the ECM is continuously trying to adjust fueling to have the O2s register 0.445 volts. The ECM is constantly hunting to see 0.445 volts. It invariably overshoots, then undershoots. All good. It's when the voltage is pegged constantly at one extreme or the other that their's a problem.

The fact that you are getting lean codes on both banks is what points me to a vac leak. It's possible for both upstream sensors to fail at the same time, but unlikely. Although I have had Bosch O2 sensors be bad when installed fresh out of the box.

Extinct, why do you say voltages need to be seen on an analog chart. I can monitor them just fine real-time with the UltraGauge.

 

Wel apparently I havent paid much attention to the o2 readouts so my prior values mentioned above might not be entirely right.

i started the car from cold overnight, and with ignition off the bank1 sensor 1 was 0.1v higher than the rest. As the car warmed up I see both front o2 sensors now reading in the range of 0.6-0.8v. My SES light automatically disappeared but the ultragauge is showing P0150 and P0130 codes now. I guess the O2 sensor values mean engine is running rich whereas the diag code means its running lean. Im so confused now

as I rev the engine the o2 voltages go down a bit towards 0.4-0.6v. At around 1900rpm the voltages fluctuate a lot.

 

I now also suspect a lean situation as a 0.835 and a 0.790 both are a good indicator they are functionng.

You can really only observe the correct functioning with an analog graph. Narrow band 02s are not precision devices, they function like a switch switching from slightly lean to slightly rich right around 14.7:1 AFR. The ECU maintains stoichometric fueling by intentionally enriching the mixture until is sees voltage close to .9 or 1.0 v and leans the mixture until it sees voltage close to 0.1 to 0.2 volts and then starts enriching the mixture again. On an analog chart you more easily see this cycle, recommend watching this video for normal operation: You need to chart it from cold start like in the video to understand do you have a sensor problem or an actual lean condition, but based on your photos I suspect a lean condition. During cold start the ECU goes very rich for a few seconds to light off the catalytic converters and then dials back the mixture after a few seconds.