Brand new O2 sensor, ran new wire from the sensor to the computer.

When I start the truck, the sensor is putting out 0 volts.

After it starts warming up, the voltage reading starts climbing.

It climbs as high as .20 volts and then usually holds there at .2 or will waver between .1 and .2 volts.

My check engine is still throwing a code 21 at me. The wire used to not read any voltage at all so it was as though it wasn't connected. Code 21 made sense.

But now, I am at least reading some voltage, but .2 seems low and lean and the code 21 is still coming after me. i did reset the computer multiple times to verify code accuracy.

What's the deal then?

Thanks.

87 22RE 5 spd EFI

In a one-wire sensor like yours, code 21 is probably triggered by a lack of switching ("lazy sensor"). Is your sensor a Bosch? If so, that's the problem - the probe is too short & doesn't get enough exhaust flow. Code 21 is common with them. Replacing with a Denso should fix it.

If not a Bosch, verify a lack of switching by following the test procedures in the O2 sensor chapter of the fsm - you need to count the number of changes of voltage off two terminals in the check connector - should be 8 or more fluctuations in 10 seconds.

Code 21 also might be triggered by an exhaust leak, or possibly a bad wiring connection.

EDIT: Since it's a one-wire sensor that tries to ground through the exhaust, measure ohms between metal body of the sensor & neg batt post. If more than a couple ohms, pinch a ground wire under a sensor mount nut & connect to a good ground. Also, you might need to use a shielded wire from sensor to the computer. The 16 ga wire here would probably be excellent for that application: http://www.aircraftspruce.com/catalo...shieldwire.php