MACS Monthly Newsletter - 2020 - MAR3

handles that too. Simply put, this is one involved BCM combined with both internally mounted and externally pluggable
(i.e. serviceable) relays as well as fuses.

Internal and External TIPM Relays

In addition to the many fuses and pluggable relays in the top
of the TIPM, several relays are buried inside the TIPM and soldered to its PC (printed circuit) board. Two PC board mounted
relays that immediately come to mind are the ones for the fuel
pump and A/C clutch operation. There are more PC board integrated relay functions on various FCA models including the
starter relay. Silicon contamination of the relay contacts and deformed relay contact springs have been discovered by Chrysler engineering and the experts at NHTSA (National Highway
Traffic Safety Administration). The PC board integrated nature
of these relays means that if one of them is determined to be
faulty, the entire TIPM must be replaced.

TIPMs Vehicle CAN Bus Communication
and Diagnostics

In addition to the functions of fuse panel / relay center, this
"computerized junction box" acts as a gateway module for
data bus traffic from the vehicle's various bus protocols. CAN
IHS (intermediate high speed) along with CAN C (high-speed)
are connected to the TIPM along with various other modules.
The actual communications we perform with our scan tools on
TIPM equipped FCA vehicles connect to pins 6 & 14 of the DLC
is via the CAN C diagnostic bus. See Figure 5.

Diagnosing a TIPM A/C Clutch Output

FCA

Before doing any diagnostics, pull all DTCs from all modules
on the vehicle. It's truly amazing how some conditions within
other systems that would "seem" to be unrelated to HVAC can
be very related. If the TIPM won't turn on the A/C clutch at all,
you'll need to look at the usual suspects of undercharge / excessive high side pressure, faulty clutch coil, open grounds, etc.
prior to looking deeper into the TIPM. Using a scan tool, pull up
the PIDs in the HVAC module related to A/C clutch operation.
Is there an "A/C compressor clutch request" PID displaying
"On", "True" or "Yes" (Figure 6, 7)? If there is not, then contain
your diagnostics to the HVAC module itself. If there is, then
move on to scanning the TIPM. Is the TIPM getting that request
from the HVAC module over the CAN IHS bus? What does the
TIPM display for "A/C Clutch Control Output"? It should be
showing "On", "True" or "Yes". If not, make sure the HVAC
control module has good powers, grounds and its CAN IHS circuits are not flatlined at ground or a higher voltage.
Figure 5: When FCA adopted the TIPM, all communications (prior to the newer models with Security Gateway
Modules) went from the DLC pins 6 and 14 to the TIPM on
a pair of CAN circuits designated as "Diagnostic CAN C."
When your scan tool communicates with ANY module on
the DLC, it is doing so through the TIPM on this data bus.

Diagnosing Intermittent TIPMs

Dave Hobbs

Prior to giving the TIPM a pass, be sure to do your best to
catch any intermittent problems. The best way to do this for
A/C clutch issues is to either have an assistant repeatedly press
the A/C request button on the HVAC control module / head or
activate bi-directional control A/C clutch requests with a scan

Figure 6: This FCA factory scan tool (wiTECH 2.0) displays data PIDs (Parameter IDs) as well as the source of that information in relationship to the module being scanned. In the case of this 2019 Ram truck's HVAC module, the status of the A/C
clutch being engaged comes into the HVAC module on a data bus (Bussed Input). The A/C clutch request is a data bus output
of the HVAC module. The Twilight Sensor Voltage (for sun load) however, is a dedicated sensor circuit into the HVAC module.

March 2020

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MACS Monthly Newsletter - 2020

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