Ok this is a second post, I'm trying to figure out if the ground for the computer re: o2 sensor is good or not. I put my meter to the :

And put one wire on d6 beige wire on the computer. ref. http://www.euronet.nl/users/fo_elmo/techno.htm

And put the other wire from the meter to a ground.

The meter reads 1018 car off, and with key in on position 1719 both steady. Meter doesn't beep as it normally does when circut is closed.

Would this mean that the ground wire for the o2 sensor isn't any good?

Second if it is no good, would I beable to cut the wire near the computer and just put it to a ground?

Any help would be appreciated.

O2 sensors in GM cars of the era tend to be purple. On my car I got one of those crimp-tap connectors and added a 1" pigtail to the O2 sensor wire at the ECM, and crimped a ring-terminal onto the 1" pigtail. That way I can hook my meter up inside the car and monitor while driving. For ground I connect to a screw that's also a ground terminal near the ECM. To read the O2 sensor make sure your meter has at least 10 mega ohms input impedence on the DC volts scale, and you need to be able to read thousands of a volt.

Voltage readings themselves aren't as meangful as the voltage swings and changes are. You want to see voltages varying from 200-300mV up to 700-800mV rapidly, crossing the 500mV point at least 2-3 times a second. If the voltage stays fixed and doesn't cycle, then there's either a problem with the sensor or the mixture is stuck way off.

As far as checking the ECM ground, just check continuity from the ECM case to the chassis, it should be zero ohms or pretty darn close.

JazzMan

So what your saying is i use one o the "or one of these" to check the wire directly off the o2 sensor. And for checking the ecm ground, I put one wire from meter and one one to ground with the meter set to the top image?

btw am visual person and not too great with these multimeters except for checking voltage o battery.

[This message has been edited by headhunter (edited 03-23-2004).]

It doesn't look like your meter will measure more than 200mV, it's hard to tell without actually using it, so I don't know if it will work on measuring the sensor voltage directly. As far as checking ground continuity and other circuit continuity, set it at the diode symbol (little arrow pointing into a straight crossbar) /speaker symbol (little arcs getting smaller). It should beep when you have the two leads on two points that are connected electrically, such as the ECM case to chassis ground.

On your meter the green settings are for amperes, which are a measurement of electrical flow volume similar to how water is measure in gallons per hour. The orange settings are for voltage, similar to water pressure. The grey settings are for resistance, and the red setting is AC volts.

Make sure the leads are plugged into the correct holes on the meter before measuring current, or you'll blow your meter up. They appear to be properly plugged in on the first pic for measuring voltage and resistance.

JazzMan

your meter is set to diode check... turn it to DC 2 volt scale. If you unplug the O2 sensor and probe between the PCM side of connector and ground with KOEO (key on engine off), you should see about 450mv. That is a bias voltage the PCM uses to verify the circuit, there is no real current behind it. The Amp settings are useless for testing an O2 signal.

Get a hatpin or a backprobe pin and with engine hot, while backprobing the O2 sensor connector (hooked up) you should see voltge responding to rich and lean signals. You need a PGM, GMM, or DSO to really test correctly as you need to see the signal switch from rich to lean and lean to rich in under 100ms. Something you can test with your meter is voltage drops and make sure the cooling system isn't acting like a battery. If you want to try that... dip a lead in the coolant and other to ground. If your meter reads over 100mv, I'd be flushing the cooling system... it's acting as a battery. The reason I mention this is that the O2 sensor is only a one volt circuit and any voltage on the system ground will mess with that circuit.

Hey I just checked the computer ground with the beep. ie 1 wire on body ground and 1 to computer case and it reads 34-47. So that would mean the computer ground isn't good?

If it is bad, where's the wire end, or would it be better just to cut the computer ground and ground it in the interior?

Ivan