> From:    Todd Last <rubatoguy@COMCAST.NET>
> Date:    Tue, 3 Apr 2007 17:29:22 +0000
>
> I've seen bad ground and shorted sensor wire mentioned in the
> references to the O2 sensor.  How does one check these wires?

There are a couple of ways to do it.

First:
VOM in "ohms" mode, Rx1 or Rx10.
Van not running.
Unplug connector at O2 sensor.
Unplug connector at ECU.
Put one VOM probe to a prong in the harness side of the O2 sensor
   connector.
Put the other VOM probe to the corresponding prong in the harness side
   of the ECU connector.
The VOM should read zero ohms or very very close to it.
Wiggle and poke at the harness while the probes are held firmly against
   the prongs.  If you find a spot that makes the VOM reading go up,
   you've found a bad spot.

Second:
VOM in "volts" mode, set for a low range like 2 V or less.
Van running.
Figure out a way to "backprobe" the connectors while the connectors are
   still attached.  Sometimes you can use a safety pin in the back side
   of the connector.  Or, poke a safety pin right straight through the
   wire - be careful that the pin doesn't ground out on anything.  When
   you are done, use some electrical tape or silicone to cover up the
   pin hole.
Put one VOM probe to a prong/wire in the O2 sensor side of the O2 sensor
   connector.
Put the other VOM probe to the corresponding prong/wire in the harness
   side of the ECU connector.
The VOM should read zero volts or very very close to it.
Wiggle and poke at the harness while the probes are held firmly against
   the prongs.  If you find a spot that makes the VOM reading go up,
   you've found a bad spot.

The first way checks the continuity of the wires, and the second way
checks the voltage drop.  The first way is easier to do, and is probably
about equal to the second way for the O2 sensor signal wire.  The second
way is probably better for the O2 sensor heater wires, as the testing is
done with a higher current than the VOM alone can provide.

Matt Roberds