need help, error code P0155, smog test coming up

[mikeh1]

'97 Sport 4.0 OHV 5/spd 151K mi, got error code P0155 "02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)", mechanic has replaced sensor, checked wiring harness and even switched with other 4 sensors (2 on left side, 2 on right), error code comes and goes, sometimes indicates short, sometimes indicates open circuit. Drove around for 6 hours, worked fine. Later, turned key to start, and same error code without even fully starting engine.

Anyone seen this problem before? I'm desperate, I have a smog test next month for yearly registration, and the Check Engine light is an instant disqualifier.

 

[mikeh1]

needed to replace PCM

turns out it was the PCM itself and one more 02 sensor, but I qualified for $500 in financial assistance from CA Bureau of Auto Repair since my Explorer is 13 years old, so it cost me $195 total. And I have an extra PCM that works perfectly except the fake error conditions, a good spare.

It's interesting watching all the problems Toyota is having with their electronics, meanwhile experiencing it first hand!