Raghorn61

I got a code 21, so I bought a new sensor put it in deleted the code but it came back. So I decided to test the sensor with a dvom and while driving it would start really low like 20mV and would steadily climb to about 340mV then would read OL and it would start back at 20mV and go to 340mV. I put the old sensor back in and it did the same thing. Has anybody have something like this happen before? Could it be a bad ECU?

scope103

Help us out here: just what are you measuring, and how?

You have a 4-wire sensor; 2 wires for the heater, and 2 wires for the actual sensor. Code 21 says you have an open in the HEATER circuit. If you stick your voltmeter on the heater wires at the sensor, you should get 12v with key-on all the time.

If you want the measure the sensor itself, there's the easy way, the hard way, and the very hard way. The very hard way involves splicing into the wiring right at the sensor; you would only do that if you suspected a broken wire somewhere. The hard way is to measure right at the Ox1 pin on the diagnostic connector. The voltage should swing between about 0.3v and 0.9v about 8 times in 10 seconds (a little fast to follow on a digital meter). The Easy way is let the ECU do the heavy lifting: http://web.archive.org/web/201003261...01heatedox.pdf (Jumper TE1 to E1 and measure voltage E1 to VF1)

Your measurements don't sound anything like what you even could get. I assume OL means "overload," which is what some digital meters show when you input a voltage greater than the range. Since almost all reasonably priced digital meters are "3 1/2 digits," the lowest range would be 2.0 volts, so OL would mean you're inputting more than 2 volts. But since you don't give the range setting, or WHERE you're measuring, you're forcing me to guess.

Raghorn61

So I decided to open up the ECU and sure enough I found the problem the resistor on the heater circuit was fried.