A buddy of mine has a stock DBC 5.3/4L60 in his 56 Bellaire. Engine runs great, but does not trim due to the O2s staying at 450-480 all the time. I loaded a complete stock tune in it with the same OS thinking something was turned off keeping it from going into CL, but nothing changed. We replaced both O2s and still no change in the MVs. Could this be a grounding issue through the O2s?
Possible Oxygen Sensor ground or power issue.
Have you checked for power at the connector?
Not yet, we ran out of time the other day. I'll have to get him back over here to do some more investigating. Does anyone have a diagram to the pinout on a 2004 1500 upstream O2? (square white 4 wire plug)Originally Posted by RDF1
Thank you! We'll line it out. I see [High signal---Low signal---Heater---Power] Are these grounded through the exhaust?
Last edited by Mingus; 04-11-2023 at 08:30 AM.
PCM provides ground circuit
Heater LOW CONTROL is ground controlled by the PCM, when it wants the heater on it completes the circuit by grounding it.
Heater low control is ground for the PCM, sometimes called low reference by GM.
And low signal is the ground reference for the signal side, it uses that as the 'zero' against which to measure the signal voltage, since there can be pretty significant ground offsets between true battery ground, ground for the power circuits of the PCM, etc. Difference between high signal and low signal = O2 voltage.
The NB O2 is essentially two electrical devices inside the same package - a 2-wire sensor, and a 2-wire heater.
I need to pay more attention to what I'm typing. Meant to say "Sensor Low Signal is ground for the PCM..."
That makes sense. I'll get with him here in a few weeks and check all the wiring.
I attached the files if you want a look.
5.3-4L60 O2s faulty.hpl5.3-4L60 O2s faulty.hpt
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