Overheating 1997 LHS solved

A while back I posted to this site about my '97 LHS cooling fans not cutting
in when they were supposed to. Checked everything, fans, relays, connections
etc. nuthin'! The problem is that the Factory Service Manual (FSM) diagrams
show only one sensor sending a signal to the "computer" (control module)
which in turn controls both the signal to the relays and the dash guage
(gage). Since the guage showed a rise in temp, it seemed reasonable to
assume that the engine sensor was working correctly.

In desperation I finally ignored that and replaced the coolant temp sensor
on the engine anyway and, presto, the fans started cutting in again the way
they're supposed to. My problem is now fixed and maybe someone else can
benefit from the experience. It only leaves me with one nagging question.
What controls the guage on the dash???

-Hank

 

--

The engine coolant temperature gauge receives its information across the CCD
Bus from the Body Control Module. The engine coolant temperature sensor
uses a variable resistor to send a signal to the Powertrain Control Module
indicating coolant temperature. The PCM then sends this information to the
BCM across the CCD Bus.

The BCM calculates the position of the engine coolant temperature gauge and
based on the information received from the PCM it adjusts the position of
the gauge pointer. This signal is sent over the CCD Bus to the instrument
cluster.

Now my question, Was the check engine lite on setting a fault code 22? was
the vehicle running bad?



Glenn Beasley

 

Hi Glenn,

The 22 code was never set and no check engine light ever came on but
whenever the temp guage read high, the engine didn't sound too happy and had
a tendency to "ping".

I know the guage is "fed" from the control module but it seems reasonable to
me that the control module gets its info from the engine coolant sending
unit (sensor). So you would think that if the guage reads high, the control
module would also send a "turn the damn fans on" signal to the fan relays.
Go figure.

-Hank