1998 S-10-E Electric Truck
EV1 System 110 Inverter/Drive train

As I investigated the DTC-279 code this past weekend (2008.07.05) I found
resistance on the HV (high voltage) negative battery box connection on the
inverter when linked to chassis ground.  I used the 200 ohms scale for this

In the first phase I tested the circuit by “unplugging” all the connectors from
the overall PIM when it was still in the vehicle and continued to get
resistance readings from the HV negative connector to chassis ground.  In
the second phase of testing I removed the PIM from the vehicle and tested it
again and received the same results.  I then went to the third phase (no pun
intended) and with the PIM out of the vehicle I started by physically
inspecting the interior of the PIM and then later began removing the
accessory modules from the PIM.  As it turns out, as I removed the power
steering control module (PSCM) from the bottom of the PIM the resistance
reading to chassis cleared.

I subsequently separated the PSCM in half (bottom and top halves), and
plugged-in the top half to the PIM and the resistance reading reappeared.  It
is now defined to the top half of the PSCM.

After disassembly of the PSCM the resistance reading vanished.  We found
that mostlikely one of the two regulator chips had a fault to ground with its
insulated mounting screw.  The insulator was replaced and the PSCM is now
functioning properly.

On the road again.

-- pictures to follow --
This shows the
resistance reading
between HV (high
voltage) negitive
and chassie ground.
This is the
resistance reading
between HV
positive and
chassie ground and
represents a
nominal reading.
Here are the
readings after the
PSCM has been
removed from teh
PIM.  Both are
nominal readings.
Here the PSCM has
been opened and
installed on the
PIM.  This shows
that the resistance
reading has
returned to the
negitive HV
terminal indicating
that the issue is
contained inside
the PSCM section
as attached to the
To confirm the
results we
removed the PSCM
and the reading
again dropped to
the meters on top,
the PIM in the
middle, and the
open two sections
of the PSCM on the
The PSCM assembly.
The PSCM halfs.
Again in halfs.
High resolution detail
on the offending
board.  1 of 2.
2 of 2