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Discussion Starter · #1 ·
I swapped an LS LM7 from 2003 Tahoe to F150 1977. (engine, fuel senders and EVAP vents into steel tank, EVAP, lines, exhaust with cats, BCM, etc)

Everything works great. The truck runs superb. Enters Closed-Loop.

I am having problems with Oxygen sensors. When the engine is cold, on the first start only I am getting all 4 oxygen sensor heater circuit malfunction errors in pending codes (P0135, P0141, P0155, P0161).
It happens only at the first start. On the second start, even after a 1-second first start, they do not come up. System I/M readiness is not checking Catalyst and EVAP. I believe this is due to Heater Malfunction as above and not getting O2 Heater Ready (however they sometimes get ready when I drive and exhaust gasses heat-up).

I did almost everything I've seen on forums:

1. Changed all four O2 sensors
2. Checked the continuity of the circuits from ECU to sensors
3. Checked the heater power turning by ECU with a bulb instead of the sensor. (Going on after crank and flashing, however, as I said, only on first cold start. Even then I go only for few seconds. Second start is not turning heating on).
4. Checked grounds, from cylinder battery to ECU grounds on ECU connector (0-1 ohm).
5. Disconnected battery for more than 45 minutes, to zero-out any memory in ECU
6. Checked sensors heater resistance (13 Ohm). Power on sensors 12V

What can be wrong? Please help. I got out of ideas.

There is one chance, that all new sensors are wrong or bad, I bought after market at eBay. However resistance is good and I got the same all 4 codes with old sensors.

Or may the PCM be bad?
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