Background:

2004 Chevrolet Silverado RCSB. The truck originally had a 4.8 that has since been swapped to an LQ4 6.0. I did not do the swap, bought the truck with the swap. The PCM and harness appear to be OEM.

Issue:

The O2 sensor heater is never activated.

Troubleshooting/Results Performed to Date:

· Confirmed all the wires and made sure they are in the correct pin on the PCM

· Confirmed the heater circuit wiring from the PCM to the O2 sensor is good.



Below are the following tests performed to arrive at this conclusion:

o I have continuity on the ground

§ Bank 1 Sensor 1 – blk/wht wire

§ Bank 2 sensor 1 = lt. Grn

o I have continuity and voltage on the power wire

§ Bank 1 Sensor 1 – Pink 12.5 v

§ Bank 2 sensor 1 = Pink 12.5 v

o I created a test light that plugs in the O2 harness for the 12v and ground signal. The test light is made of an O2 pigtail, 7440 socket and 7440 bulb. This made it easier for me to see when the circuit would be active or not. With the test light connected, turn the key to the on position, engine not running, test light does not come on. Engine running ,light does not come on.

- Pulled the connector from the PCM and back fed ground from the battery to the O2 ground terminal and the light will come on

Tested PCM grounds with multimeter and confirming continuity from pin out to the battery ground cable.

o PCM Connector 1 (Blue)

§ Pin 1 – Ground circuit is good

§ Pin 24 – Ground circuit is good

§ Pin 27 – Ground circuit is good

§ Pin 40 – Ground circuit is good

§ Pin 64 – Ground circuit is good

§ Pin 67 - Ground circuit is good

o Connector 2 (Green)

§ Pin 1 – Ground circuit is good

§ Pin 40 – Ground circuit is good

Next Steps:

Here is where I need direction. Hoping someone else has had this experience and can share how they resolved this issue. I feel like I am honing in on my root cause but, just not quite there yet. I believe the issue is either the PCM or a signal issue that I have not uncovered yet.

Thanks in advance.

Larry

 

Check the engine sensor fuse, are there any other DTC’s?

 

Are you referring to the oxygen sensor fuses? If so, I have checked those and they are good. I am getting 12v to the O2 plug.
If not, could you be more specific? I am not clear what you are referencing.

 

Data trouble codes(Engine light). Anything else giving you a code?
Also do you know what is done to the tune? You realize it needs to be in closed loop for your o2 sensors to read. If your in open loop that could be while your not getting a signal.you may want to read into closed loop/open loop.

 

Only codes are those referencing the oxygen sensor heating circuit not working.

 

Your sensors may be bad putting the truck in open loop or something may be done to tune causing this.

 

Sensors are new. I bought a pair of Denso sensors in the beginning. I had read somewhere that after market sensors could present this issue and the recommendation was to use the OEM sensors from GM. So, I bought a pair of GM sensors and still have the same issue.

 

are you sure for some reason your truck isnt tuned open loop? That would disable the o2 sensors.

 

Hhmmm, I will be contacting the tuner to confirm and will report back.

 

I have talked with the tuner and he tells me there isn't anything in the tune that would turn off the O2 heater. I have further confirmed this with Brendan at LT1Swap. I provided him with model /part # of my PCM and he says there isn't a setting to be able to turn of the O2 sensor heater as well.

So, either there is something wrong my PCM or it isn't being triggered to send the ground signal. Anyone know what triggers the ground signal from the PCM?

 

I have talked to my tuner and he stated that there isn't a way to turn off the heater circuit for the O2 sensor. I reached out to Brendan at LT1swap and he also confirmed there isn't a way to turn off the heater circuit for the O2 sensor.

Either the PCM is not receiving the trigger to send the ground to the O2 sensor or the PCM is bad.

Anyone know what triggers the ground from the PCM to be sent the O2 sensor?

 

I have received confirmation there isn't a way to turn off the O2 heater in the Tune.

Anyone know what triggers the PCM to send the ground signal to the O2 heater?

 

Your truck definitely can be staying in open loop and that definitely can cause the o2 sensors to not work. Is your thermostat working correctly? Are the maf and map sensors reading correctly? Your tuner should of asked you for a data log not a part number. Anytime I have any issues with my truck the first thing my tuner does is hook up his computer and he is always able to help me trace down the issue that way. Go on Google and do some research on open loop.

*my google search of your issue.

Yes, a 2004 Silverado can be stuck in open loop if the new oxygen (O2) sensors aren't reading correctly due to issues like faulty wiring, bad sensors out of the box, or a problem with another sensor like the mass airflow sensor or coolant temperature sensor. Other issues could be an exhaust or air intake leak that creates a false lean condition, or even a problem with the engine control module (ECM). Potential causes and solutions Faulty new sensors: Even new parts can be defective. A simple test is to swap the left and right upstream sensors to see if the problem follows the sensor. You can also check the signal with a multimeter to see if the voltage fluctuates between \(0.1V\) and \(0.9V\); a steady or zero reading indicates a bad sensor.Wiring issues: Broken wires, loose connections, or short circuits can disrupt the signal from the O2 sensor to the ECM, preventing it from entering closed loop. Check all wiring harnesses and connectors, especially after replacing the sensors.Other sensor failures: The upstream O2 sensor is critical for entering closed loop. However, a failure in other sensors like the mass airflow (MAF) sensor, intake air temperature (IAT) sensor, or coolant temperature (ECT) sensor can also keep the truck in open loop.Air or exhaust leaks: Leaks in the intake system or exhaust system can create a false lean condition, causing the ECM to stay in open loop to try and compensate. Look for any obvious leaks around the new sensors or elsewhere in the exhaust and intake.Engine Control Module (ECM) problems: In some cases, a failing ECM can be the root cause of the problem, even after other issues have been fixed.Incorrect installation: If the new sensors weren't installed properly, it could cause issues. For instance, applying too much thread locker can interfere with the sensor's ground. How to diagnose Swap sensors: Swap the left and right upstream O2 sensors to see if the fault follows the sensor.Check wiring: Visually inspect the O2 sensor wiring harnesses for any signs of damage or loose connections.Monitor sensor data: Use a scan tool to monitor the data from the O2 sensors, as well as fuel trim percentages, MAF, and IAT values. Look for the sensors to stay at \(0V\) or fluctuate erratically.Check for leaks: Perform a smoke test on the intake system and listen for exhaust leaks.Reset the codes: After addressing potential issues, use a scan tool to clear any stored codes and reset the ECM.

 

Open loop does not cause an o2 sensor DTC. His problem is almost always a wiring issue. It could be anything from a bad ground, to rodent chews, to corrosion on the pin at the PCM. No way to tell without spending a lot of annoying time with a multimeter. And that is all assuming good sensors. Although it is possible, this problem is almost never the pcm.

 

Run a temporary 12v and sensor ground from the ecu then and see if it comes on. It takes all of about 5 minutes to run a few wires outside the truck.

 

I came across a post in a forum where someone experiencing the very same issue had a solution. I wanted to run it by you guy's first as the post indicates this worked but, did not provide any technical reason as to why this worked.

The Post:
“What seems to have fixed the problem is to use the trapezoid plugged O2 sensors (in the front only) from the 6.0 equipped GMT800s of these years.
The 2004 Yukon 4.8 has square plug O2 sensors.

I bought some extensions on eBay cut and spliced them to the old O2 sensor plugs. That way I didn't have to modify the vehicle's harness (or the sensors). The plugs have letters marked on them (faintly). A:A, B:B C:E D)

Part # for the Denso sensors OP used: 234-4669.”

To me, one 4 wire sensor would be the same as another regardless of plug configuration. I realize that may be a very naïve perspective. More the reason I wanted to run this with you guy's before any action is taken as I don’t want to cause any harm by trying something without knowledge of why it should work or knowing this will cause harm by going down this path.

My truck has the square plug as well. Here is a wiring diagram B1S1 sensor for reference:



The Trapezoid plug wiring diagram for reference:

The obvious difference is the square plug pin D ignition voltage would become Pin E on the Trapezoid plug (wiring splice reference from above - A:A, B:B C:E D) which is the heater low control. This difference in the trapezoid style sensor be what is needed in my situation to trigger the heater to be activated?

I am hoping you guy's can either tell me this absolutely dumb and I should not pursue this or tell me this makes sense to you and this could be a potential solution I have been looking for.

Appreciate your thoughts.

 

As mentioned in my original post, I did the following:

o I created a test light that plugs in the O2 harness for the 12v and ground signal. The test light is made of an O2 pigtail, 7440 socket and 7440 bulb. This made it easier for me to see when the circuit would be active or not. With the test light connected, turn the key to the on position, engine not running, test light does not come on. Engine running ,light does not come on.

- Pulled the connector from the PCM and back fed ground from the battery to the O2 ground terminal and the light will come on

 

There is a forum on here called no power to o2 sensors. Maybe read that, looks like his issue was a ground on the cylinder head.