A diodes failure mode is shorted, if it reads shorted in both directions then it's bad.
Go to Vmaxoutlaw, tech and info, sevice manual, page 321 and on.
Page 324 has the diagram and procedure for checking diodes.
It's gonna tell you to use thier "pcoket tester" what they are asking for is a analog meter that has enough voltage on the continuity/resistance function to forward bias a diode. You can also use a digital meter if it has a diode check function.
There is an easier way tho' I use it when troubleshooting UPS systems.
A diode has only one failure mode and that is "shorted"
If you have a digital meter DO NOT put it in the diode check function, just put it on a lower resistance scale. The voltage output won't be enough to bias a diode so it will read open no matter what polarity you are using.
Put one lead on the positive wire and then check each white wire.
Then put one lead on the negative lead and check to each white wire.
If you read continuity anywhere you R/R has a shorted diode.
This will not work with an analog meter because it will "turn on" the diode.
Rusty
