Can't figure O2 sensor

[gabequest]

P0140 Code: Replaced sensor behind catalytic converter, drove 20 minutes no check engine light, then back on. Drove like this for a while then decided to try another sensor. Same result: off then on and stays on. My tool says "no activity detected". Both mine and a shop's read this code and no codes for the cat.
I checked fuses for continuity and voltage: both good.

What may the issue be???

Some background...5.7 swap, tranny swap but still 4L60E and check engine was on before this swap. The sensor is for specs from swap: 5.7L suburban 1500, 4L60E.

Also...but not associated..."anti-lock" light on...ideas about this?

[SafariRob]

My 89 is too old to have an O2 sensor downstream of the cat, but, if I understand correctly, the sensor in this location is to monitor the workings of the catalytic converter. If this is true, then I have to wonder if the cat is doing its job anymore. Beyond that, I could see where the O2 sensor wire that takes the sensor output to the PCM might be open.

[gabequest]

Hmm....should I then search for a ground issue? Not sure how to do that.

[LiftedAWDAstro]

The bad catalytic converter code is P0420 not P0140. P0140 is :O2 sensor CKT No Activity (Bank 1 Sensor 2). Bank 1 is driver side, sensor 2 would be the one in front of the converter I think.

[gabequest]

Dean:
I believe sensor 2 is behind the cat. Sensors 1 for banks 1, 2 are after exhaust manifolds, before the cat.

Also, I unplugged and checked voltage at the connector coming from harness to sensor and had nearly 12 volts with van "on", so assuming that at least power is not an issue.

[LiftedAWDAstro]

Really the only way to verify the O2 sensor is working is to have the van running with a scanner looking at the O2 readings. The voltage should be varying between 0 and 1 volt and should not be steady.

[gabequest]

A local mechanic used his GM scan tool with the van running and showed the same code. He was unable to read the anti-lock code with his scanner and wonders if a ground is bad or if there is a problem with the ECM.
I'd like to go about checking grounds, but I'm overwhelmed by the wiring diagrams in my HAYNES. If I knew how to read them I could pull it off, but most definitely confused.

[gabequest]

Disconnected the blue plug from ECM, turned engine over, plugged back in and started: no codes other than ABS. Drove about 8 miles to auto parts store. Sprayed connector cleaner on both parts of each O2 sensor and all ABS connections. Drove 5 miles and and SES light back on. Also, driving up hill the van wouldn't downshift so power was not available. Now reads PO131 (low voltage) instead, and the PO141 is now a "pending"code . What the F is going on here?!

[gabequest]

As a continuation (so to speak) of my other reports about "can't figure out O2 sensors".........

My confusion...PO141 is bank 1 sensor 2, 151 is bank 2, sens 2. Since sensor 2's are downstream of cat converter, but my van has only one cat...what does this mean?

My PO141 has been there a while...shows "no activity detected". There is power to sensor via the harness but my scan tool shows 0 volts during operation, so the feedback (pink wire on harness I think) must not be sending. How do I check that?

Also, PO157 confuses me because I feel like I don't technically have that sensor present.

I had the PO131 and PO157 after unplugging BLUE connector to ECM, but got rid of 131 after pulling the plug and spraying silicon. Also checked to make sure pins were not pushed in. Was hoping 157 would disappear too, but still there.

Some have said PO141 may be bad ECM. I've tried 2 Bosch sensors and am waiting for AC DELCO from amazon to try OEM, since I've heard occasionally the Bosch sensors don't read.

Any advice would be appreciated, especially on how to check continuity from the sensor end of harness to ECM...isn't there a relay in there too?

[v8famvan]

Since you are running a V8 in this van, this is where you have to look.
The issue is this: The V8 computer that I assume you installed in here is from a truck. In a truck there is 2 cats & 4 O2 sensors. In the 4.3 vans there is 1 cat 3 O2 sensors. The computer is 'looking' for the missing O2 sensor. Since it is not there, this is affecting the other readings on the other sensors.
How to fix, custom reprogramming of the computer.

[gabequest]

thanks for the ONLY reply!!

I too feel that is the problem. Unfortunately I've moved to CA and the guy who reprogrammed the ECM is still in Denver. That would have been too easy! Maybe I'll plug the computer and send it to him so he can mask that sensor.

In terms of PO157: low voltage bank 2 sensor 2 (i think)...this code just recently came on, so not sure why? Even after replacing that sensor with AC DELCO. Any thoughts on that? Seems too delayed to have come from the other sensor/cat issue, which has been there for months.

thanks,
Gabe

[sfeaver]

According to a picture in the GM parts catalog, there is a seperate cat for left and right sides of the motor, and each one has a o2 sensor behind the cat.

Reprogramming would be the best fix, but I wonder if there is a way to feed the same signal to both inputs so it see what it wants to see.

This is a swap im planning on starting soon so if I come up with something I'll let you know. Reprogramming is the best fix though in my opinion.

Scott

[LiftedAWDAstro]

thanks for the ONLY reply!!

Umm Gabe...you started a second thread for the same issue...maybe that is why you didn't get a response. That and the technical workings of the ECM's is way over most of our heads since we are not GM trained. James is definitely the man for the job though.

EDIT: I merged the 2 threads so there is a continuation of the whole issue. As you can see we tried answering your problem.

[v8famvan]

Umm Gabe...you started a second thread for the same issue...maybe that is why you didn't get a response. That and the technical workings of the ECM's is way over most of our heads since we are not GM trained. James is definitely the man for the job though.

EDIT: I merged the 2 threads so there is a continuation of the whole issue. As you can see we tried answering your problem.

Thanks Dean for the merge & the supporting comments...

In terms of PO157: low voltage bank 2 sensor 2 (i think)...this code just recently came on, so not sure why? Even after replacing that sensor with AC DELCO. Any thoughts on that? Seems too delayed to have come from the other sensor/cat issue, which has been there for months.

thanks,
Gabe

I have posted some of the following information from the GM service manual that might help you understand what is going on here.
_______________________________________________________________
What causes this code to set:
This DTC is designed to detect an HO2S voltage that remains at a low (lean) voltage for more than 110 seconds during a 130 second test period. This DTC is set under the following conditions:

• There is an HO2S circuit fault that results in a false lean exhaust condition.

• The HO2S is correctly detecting the lean air/fuel ratio resulting from either a vacuum leak or a fuel control system problem.

Diagnostic aids/common problems
Check for the following:

• HO2S wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold

• Intermittent ground in the wire between the connector and the sensor

• Poor VCM to engine block ground

• Lean injector(s). Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test .

• Fuel contamination. Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can also set this DTC. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• Fuel pressure. System will be lean if pressure is too low. It may be necessary to monitor a fuel pressure gauge while driving the vehicle at various road speeds and/or loads to confirm. Refer to Fuel System Diagnosis .

• Exhaust leaks. If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Refer to Exhaust System Inspection in Engine Exhaust.

• Vacuum or crankcase ventilation system leaks can cause a lean condition and/or possibly a high idle.

An intermittent may be caused by any of the following conditions:

• A poor connection

• Rubbed through wire insulation

• A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint.
_______________________________________________________________
Based on my experience, I suspect the problem likely a wire that is chaffed to ground. Monitoring the post cat O2 sensor reading would aid in confirming the fault.

[astrozam]

Excellent info