Have spend over a man day rounding up equipment and attempting to determine why scan tools will not communicate AND if PCM is good. (If PCM is good, am sending it out for a tune on a mild heads/cam/exhaust 511 whp Viper.

Problem is somewhat intermittent:

  • July 2019: DRM and SnapOn scan tools failed to communicate in Nevada
  • Week later, DRB communicated.
  • End of July drove car 2500 miles from NV to PA
  • NOW DRB (and a SnapOn) fail to communicate and hangs w/"The PCM is not supporting..." message page.
  • Installing DLC Break Out Box got the DRB further into the windows to Engine but failed there.
  • DRB fails to communicate and hangs w/"The PCM is not supporting..." message page.

Car has a Roe Racing VEC-1 installed. Soldered MAP signal connections. Vampire piercing connections for the LED A/F Gauge. I have checked this a year ago when the DRM was communicating and it appeared to be functioning perfectly.

Trying to determine if PCM is good. Car appears to run OK, but DRB hangs after failing to communicate producing a page starting with: "The PCM is not supporting Scan Tool Communications" when 1996 year specific diagnosis is requested. Snap-On scan tool also failed to comm. NOTE: DRB mode Generic Scan Tool does bring back 32 parameters including ECT of 106* and IAT of 46* which are expected values.

I know K-Line is 12v (off) and 0v (on) and is dormant when nothing is being requested - in fact, it is frequently mistaken for a Vbattery

I don't know if L-Line is used.

I am using the DRB Break Out Box.

1st session I found Vbat on K-Line and 5v on L-line w/no scan tool connected. I think this was with Ken On only but possibly might have been running.

Next day 2nd session found a meandering DC + AC within a 0-4v range on both K and L, either Key On or Running, I'm forgetting now.

Attempts of moving connectors, contacts, etc. in the hope of seeing Vbat again resulted on 0v on both K and L, Ken On AND Running.

Guide to DRB III p.27 states that when communication fails, "Refer to the appropriate Vehicle Communicatios diagnostic Manual for he vehicle you are servicing." I've found no such document for my 1996 Viper or any 1996 model. I really need this information/manual!

I need to know what K & L do when 1) Ken On, 2) Engine Running, and 3) DRB requests.