Fault Code Guide

General Information
The Chassis Module (CHM) and the Expansion Mod-
ule (EXM) both serve the same function in the M2
electrical system by acting as slaves to the Bulkhead
Module (BHM). The CHM and EXM respond to com-
mands from the BHM and broadcast the status of the
inputs and outputs that are sent to and delivered by
the modules.
A Business Class M2 vehicle will always have a
Chassis Module, but will only have an Expansion
Module when optional features require it. The CHM
and EXM both have five harness connectors, though
they may not all be used.
Chassis Module
The CHM is usually mounted on the left frame rail,
aft of the cab. See Fig. 1. The CHM is available in
two configurations depending on the vehicle options:
• standard Chassis Module
• full Chassis Module
The vehicle will have either a standard CHM or a full
CHM, but not both. The standard CHM uses only the
C1, C3, and C4 harness connectors. The remaining
harness connectors are sealed. See Fig. 2.
Both the standard CHM and full CHM are supported
by one version of software.
Alternate Mounting Location of the
CHM
On some M2 vehicles the CHM is factory installed
under the cab instead of on the frame rail behind the
cab. This alternate location affects the C5 connector
on the CHM, which controls any air management unit
(AMU) solenoid that the vehicle may be equipped
with.
When the CHM is mounted on the frame rail behind
the cab, the harness for the AMU solenoids plugs
directly into the C5 connector on the CHM. When the
CHM is factory installed under the cab, a jumper
loom is required between the plug coming from the
AMU solenoids and the C5 connector on the CHM.
The jumper loom is part of the forward chassis har-
ness that is used with the CHM when it is factory
installed under the cab. The jumper loom has generic
circuit numbers and is present regardless of whether
or not the AMU circuits are used on the vehicle.
NOTE: See Specifications 400 for information
on how a factory-installed CHM under the cab
affects the wiring.
09/28/2001
f543919
1
2
3
4
5
1. Chassis Module
2. Left Frame Rail
3. Cab Backwall
4. Crossmember
5. Driveline
Fig. 1, Chassis Module Installation on Frame Rail
09/11/2001
f543900
1
2
3
4
5
1. C1, Taillight Harness
2. C2, Trailer Module Harness, Full CHM Only
3. C3, Forward Chassis Harness
4. C4, Forward Chassis Harness
5. C5, Air Management Unit Harness, Full CHM Only
Fig. 2, Chassis Module Harness Connectors
Chassis Module and Expansion Module 54.13
General Information
Business Class M2 Workshop Manual, Supplement 10, September 2006 050/1