Thanks. This is extremely helpful information. I just ran a temporary positive lead from the drivers bank o2 fuse 16 to the sensor. It didn't fix my issue, so it must be on the ground side, or the pcm itself. I don't think the pcm would be able to determine whether the fault is from the positive side or the ground going to it since p0030 is an open circuit code, but hey, maybe its a wizard.

It's funny you mention the o2 relearn procedure. I wonder if the dealer ever did that when they replaced the sensor and the wire. I also wonder if the new wire could also cause this problem as the gauge might be different therefore causing a different resistance in the heater circuit that would make the pcm think something's up hence the "The ECM detects that the affected HO2S heater low control circuit is not within a specified range"

A little besides the point, but dealers and mechanics have aggravated me a lot recently. You ask them to do the simplest things and they somehow manage to f*ck it up. More than three times we've been back for this. When they ran their new wire, it went right in the wheel well, unprotected, loosely zip tied(metal on wire) to fuel lines and other places back to the sensor. I asked them to use some common sense and put it in a loom the next time i came in. And believe it or not when it came back out, they used about a foot of loom ONLY in the wheel well, and they completely ignored the other 6 ft of wire zip tied to metal. They didn't even bother to tape the loom, so it fell off the little wire a week later.

Lesson learned: If you want it done right do it yourself. I should just take it back and stand over the mechanic's shoulder while he does it.

 

Gavin Costigan essentially you are correct, though not necessarily an open circuit, it actually refers to the "Heater Control Circuit" it could mean the PCM is struggling to maintain the heater current.

The following info may help diagnose your problem.

So I measured the following on Bank 1 Sensor 2:-

1. The heater resistance measured 12.7Ω (cold) [sensor 2 was quicker and easier for me time-wise]
2. The internal resistance of the PCM's input on (C2 Pin 72) made by measuring between chassis GND and Pin C (GND) of the Sensor Harness Plug, this was 10Ω [could be KEY!]

The Tech2 also provided the following data (below) [Note the "Learn" feature doesn't seem to be available (at least for an '05) so I think we can forget about that]



As can be seen, the upstream sensors draw 1.0 Amps and down-streams 0.6 Amps. The Ignition Voltage was 14.2V for reference.

The electronics inside the PCM probably measure the voltage across it's internal 10Ω resistor thus using this to regulate the heater current (PWM) So for the downstream Sensors the PCM's internal reference works out to be 6V ( i.e. V= I x R)

[Note the heater resistance seems to increase to13.7Ω when hot]

So:-

1. Measure both upstream Sensor heaters (Pins C + D) record and compare their resistances. These are likely to be between 7.0 to 8.2 Ω (maybe)
2. Measure both PCM's input resistances i.e. between Pin C of the Sensor Harness plug and the chassis (transmission casing will do) Again these are likely to be between 5 to 6Ω.

[Note estimates are based on the PCM using the same internal voltage reference of 6V for all HO2S sensors]

If the upstream PCM input resistances are same (or very close) then these are the likely possibilities:-

• There is an intermittent wiring fault. You can check by measuring the PCM's internal resistance whilst and pulling/moving the wiring.
• A bad/intermittent sensor.
• A fault with the PCM

It should tell you a lot:-

1. The sensor heaters are the correct values and their wires and plugs are OK
2. If the PCM wiring and internal resistance are OK it will rule out any "thin" wiring issues (but not an intermittent break)

[Note It seems like lots of work, but it's only 4 measurements and may reveal much about the problem]

Alternatively a Teck2 could help as it can plot the sensor current on a graph whilst driving along, you may see a "dip" with each DTC

Please feed back any data for reference.

ps

Just for ref the heater Pins C+Dare highlighted below.

 

If you have power at PIN D, check for ground PIN C. Do you have power and ground(harness side)?



Probe PIN C and PIN D of the SENSOR side of the oxygen sensor. By measuring the internal resistance of the o2 sensor, it should return a value between 5 to 16 Ω (Ohms). If the measurements fall outside of this range, replace it.

 

It's subtle, but important to note, that Pin-C does not connect directly to ground, rather it passes via an internal resistor within the Power-Train Control Module (PCM) to ground.

The PCM measures the voltage across this resistance to calculate the heater current. Internally the circuit may comprise of a discrete resistor in series with a MOSFET, or simply a MOSFET on it's own. Either way, the PCM measures the current and Ignition Voltage to calculate the power dissipated by the heater (V x I) The MOSFET Pulse-Width-Modulates the current to keep the heat generation constant.

Pin-C will not read 0Ohms to ground, nor can it be jumpered to ground i.e. bypassing the PCM input.

It's worth checking exactly where the dealer's extra wire connects to, if one end connects to Pin-C the other end must connect to PCM C2 Pin-72 otherwise it will never work.

 

Probe WIRE from Pin C to PCM should be -0- Ω

 

 

The dealer connected the wire from Pin C to some pin on the pcm which I'm assuming is the mosfet low control. At this point that's all it could realistically be. I think I'm going to chance one more time taking it back this week for them to fix it and do it right. I don't want to touch anything they did just yet because I have no intention of paying for anything, and I don't want them accusing me of causing the problem.

Edit: Also do you have any higher quality images of the entire circuit diagrams you sent earlier? Even if I download them, the quality is too low to make out any of the words, and it would be a nice thing to have.

 

Gavin Costigan the original pdf was based on 4 separate pages screenshots, hence the low-res and poor PDF.

Using 1/2 page screenshots, lots of cutting and pasting, I eventually managed to improve the resolution, closer to the original pdf. Please let me know if this is OK now.

I support your sentiments with the dealer, if however that goes nowhere, seriously just make those 4 measurements, it shouldn't take too long.


@hummerz
Enjoyed watching the ChrisFix "sound alike" video, he even uses the same latex gloves and Snap-On tool box. Would love to see him though do a re-make same using an old Avo Model 8, now that would be interesting

However he did have a rather impressive $400 4½ digit True RMS Fluke 87-V which I fully endorse.

Fluke undoubtedly make the best multimeters in the world, they 1st introduced them to the UK around 1973, but met with some resistance (excuse the pun) from the old die-hards engineers who clung on to their old Avo's.

These old fogies protested saying things like :-

• "You can't beat the old Avo!"
• "What good are microprocessors?"
• "Exactly what can you use a laser for?"
• "FET's will never catch on!"

Those were the days of thermionic valves, slide-rules and cathode ray B+W TV's

Time, of course, changed everything, when I 1st demonstrated a Fluke reading a standard laboratory reference cell more accurately than the cell itself, the old fogies eventually capitulated (but still kept their Avos)

Fluke eventually acquired and rebranded the Philips Scopemeter range, I still have an original Philips PM97 which I bought back in '76, I won't bore you with the detail, but I managed to fix it using a rather helpful YT video titled
"Philips / Fluke PM97 - Keypad Repair and Backlight Replacement" he doesn't seem a bad guy, boring perhaps.


I also have a Fluke 83 which is my rock and pillar. One nice feature is its "Fast Ohms", a low ohms "beeper" and a Diode Test that will illuminate most LEDs as it uses a 4V constant-current,source, unlike the cheaper multimeters


Excuse my reminiscing but it was inspired by the young whipersnapper in the video, having said that he's got over 1 million views and 12K likes, well done to him!

Yes indeed the wire from Pin-C to the PCM should measure 0 Ohms or thereabouts, there's always some resistance in the loom wires and meter test leads, so it may realistically be around 0.4 ohms ish.

Measuring to the PCM directly could be a tad tricky, plus it doesn't account for the PCM's internal resistive connexion to GND.

Probing from Pin-C to the actual chassis GND will include all the wiring, the connectors, pins and contacts, and any solder joints on the PCM's PCB etc.

If I get time I'll pull an upstream sensor, run some more checks and get more data.

 

"Probing from Pin-C to the actual chassis GND will include all the wiring, the connectors, pins and contacts, and any solder joints on the PCM's PCB etc."

I'm going to check what I said above because access to the loom Pin-C was tricky and hard to see, so I need to check it wasn't Pin-A I was measuring.

 

You should print this thread out and show it to the dealer and tell them that the Hummer community is watching for them to make it right.