No closed loop
No closed loop I have an 02 LQ4 in a K5 Blazer. It's DBC, 4l60 starts runs nice but won't go into closed loop. The codes are for no activity for both O2 sensors. They are new Denso sensors, the scan tool shows activity with voltages running .437 to .463. So that to me seems to be conflicting info. The scan tool shows O2 heater as not ready in the emissions readiness. Pulled one if the sensors and applied 12vto the heater circuit and it heated up. I'm open to suggestions. I have ground to the block at the sensor plug I also have switched 12v+ at the sensor plug.
They are the correct sensors for that PCM. Canadian VIN with Canadian application sensors. when I made the harness standalone, I didn't change how the sensor were grounded. In this application they are grounded through the ground system to the cylinder heads.
If they are showing that mv they aren't doing anything and probably aren't wired correctly. When then aren't plugged in they will default to 450mv or so.
Did you cut the stock harness down yourself or have it done.
There are several things that will cause this problem but I speculate it's the wiring harness.
Did you cut the stock harness down yourself or have it done.
There are several things that will cause this problem but I speculate it's the wiring harness.
TECH Regular
Joined: Dec 2011
Posts: 420
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I ran into the same (ironically, swapping an LQ4 into my 1971 K5..).. I ended up with sensors and harness that wanted isolated ground but the ECU was not grounding them, expecting case grounds. I had to do some jumper wires at the ecu to get ground to those wires, then it was fine, that it that way for 2 years before swapping to Holley. (My harness, ECU, Engine, and O2 sensors were all separate purchases). I believe my engine and O2s were for Blue/Green ECU, but my harness(painless)/ECU were Red/Blue.
This is the 18th harness that I've done. The harness wiring to the sensors was shortened but never changed as to where it terminates, ie in this case to the cylinder heads not the PCM. Both sensors are reading rapid fluctuations between .437 and .460 volts as though the PCM was reacting to their input. That aren't flat line at a voltage. Wiring has been verified to match the schematic for that year. The sensor plugs in the harness require sensors for a Canadian built vehicle and the PCM shows that it is in fact a Canadian built vehicle based on the VIN starting with a 2. The heater circuit wires show battery voltage with key on and the ground for the heater circuit is good. With the sensors plugged into the harness they get hot with the key on but it takes over 2 minutes with them on like that before they get too hot to touch. So, scan tool shows activity on both sensors, heater circuit heats thee sensors, that removes wiring from the equation. But I get no short term or long term fuel trim activity. And the scan tool also shows O2 heater not ready in the emissions readiness. Is it possible that the sensors simply are not getting hot enough?
In your case the blue green PCM was looking for ground at pins in the PCM. A harness for the blue red would have had them grounded to the cylinder heads. So that would be an issue. The harness and PCM are all from the same vehicle and sensors were bought to match the PCM. I appreciate everyone's input on this! You are confirming that I'm checking the right conditions.
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Joined: Feb 2004
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From: Sweden
On some vehicles the O2 sensor heater diagnostic does not actually check the heater current/power, instead it looks for time to activity. If too long, it's interpreted as faulty sensor heaters. Are the O2 sensors located further downstream than the original position? If so, that may be the reason for not setting the heater readiness code.
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Verdad Gallardo On some vehicles the O2 sensor heater diagnostic does not actually check the heater current/power, instead it looks for time to activity. If too long, it's interpreted as faulty sensor heaters. Are the O2 sensors located further downstream than the original position? If so, that may be the reason for not setting the heater readiness code.