97 Mustang electric fan not working properly

betelgeuse

New Member
Mar 28, 2010
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Ok here's my situation that I have struggling for a year now

I have a 97 Mustang GT 4.6 SOHC

1) When the a/c is switched on the Engine cooling fan turns on at low speed
(cable Red Orange) instead of turning at high speed.

2) If I don't turn on the a/c, the fan will not turn on and the engine will overheat
(this has already caused me to replaced the intake manifold)

What I have done:

a) If I disconnect the Engine coolant temperature sensor the fan turn's on at High speed
This shows that the fan (at high speed), the HDEF relay (in the CCRM), the fuses that feed the system work and that at least the PCM is able to detect an open circuit in the temperature sensor circuit.
Temperature Sensor internal resistance does decrease as engine gets hotter.

b) Have replaced the Engine coolant temperature sensor (right sensor)

c) Have replaced the Constant Control Relay module

And the result is still the same

Has anyone have any ideas?
 
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Please answer all of the questions as there are several factors that could be related.

Is the fan correct for the MY? Ford did make changes in the fan design. As well as there are difference between the V8 and V6 fans.

Has the correct temperature sensor for the MY has been used?

Are you positive the CCRM used is correct for the MY? Are there any other parts used that are from different MY? Again, some changes have been made between the different MY's.

Are you running a custom tune? Has any changes been done to the fan set points?

We really need to know what the temperature is as reported by the PCM. Use an ODB2 scanner.
 
Finally got OBD2 Scanner

Hi wmburns

Thanks for the reply, sorry that I took so long to respond but I took me some time to get the money for the scanner, anyways here are the responses to your quetions

1) Yes its the correct fan for the Car (acording to the local Auto parts store).

2) Not sure what's the correct temp sensor part number is,
The one currently in the car was given to me by the AutoZone sales guy by model year (which is probably wrong).

3) The CCRM is F6SF-12B577-AA which as far as I can tell, (after searching the web) is the correct one for the Mustang 97 (the previous CCRM has the same part number)

4) No it has the standard factory settings.

5) The temp reported by the OBD2 Scanner is - 40 F
It also shows the following 4 codes.
P0118 Engine Coolant Temp (Circuit High Input)
P0401 EGR Flow insufficient
P0118 Engine Coolant Temp (Circuit High Input)
P0401 EGR Flow insufficient

View Freeze data
DTC that caused Freeze frame P0118
Engine RPM 1250
Load Value 14.5%
Coolant Temp -40 F
Short Term Fuel Trim 1 10.9%
Long Term Fuel Trim 1 0%
Short Term Fuel Trim 2 10.9%
Long Term Fuel Trim 2 0%
Short Term Fuel Trim 3 82%
Long Term Fuel Trim 3 50%
Short Term Fuel Trim 4 75%
Long Term Fuel Trim 4 57%
Vehicule Speed 0 mph
Fuel System 1 Open
Fuel System 2 N/A

I/M Monitors
Misfire Monitor ok
Fuel System Mon ok
Comp Component ok
Catalyst Mon ok
Htd Catalyst N/A
Evap System Mon N/A
Sec Air System N/A
A/C Refrig Mon N/A
Oxigen Sensor Mon ok
Oxigen Sensor Htr ok
EGR System Mon ok

Any advice would greatly appreciated.
Thanks
 
The clues to the problem are:

P0118 Engine Coolant Temp (Circuit High Input)
Coolant Temp -40 F

Note the MINUS 40 degrees. (that is unless it really is -40 where you live).

This is almost surely a wiring problem between the PCM and the temperture sensor or a bad sensor.

Inspect the wiring and the connector to the temperature sensor. Look for bent/pushed pins, chaffed wires, or anything else can interrupt the signal.

For the EGR problem, check the vacuum lines to the DPFE.