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A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 6212
Experience:  ASE Master Certified, ASE Advanced Gasoline Engine Performance
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I'M having issues with the cooling system on a 2003 Focus

Customer Question

i'M having issues with the cooling system on a 2003 Focus 2.0L DOHC
JA: Has the car been overheating? Have you noticed any leaks?
Customer: no leaks. It has code P1290 and I changed the CHT sensor
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Yes. Changed the temp sensor and the fan motor resistor
JA: Anything else you think the mechanic should know?
Customer: Almost as soon as I start the car the temp gauge stops working and the fan comes on
Submitted: 4 months ago.
Category: Ford
Customer: replied 4 months ago.
Also the a/c won't turn on
Expert:  A. Penland replied 4 months ago.

Have you been able to check for any trouble codes in any of the modules on the vehicle?

Customer: replied 4 months ago.
code P1290
Customer: replied 4 months ago.
It acts as if it's already overheating as soon as I start the car. The temp gauge stops working, the fan comes on and the a/c won't work.
Expert:  A. Penland replied 4 months ago.

Just wondered if you had any other codes besides P1290.

Was the sensor you replaced behind the alternator on the cylinder head?

Customer: replied 4 months ago.
I just checked the codes again and got P1289 also, cleared the codes and P1290 came back. Yes the sensor behind the alternator
Expert:  A. Penland replied 4 months ago.

Ok. We will need to check the wiring between the CHT sensor and the PCM (Engine Computer) which will require a digital multimeter that can measure dc volts and OHMS (resistance). DO you have a meter? Since the sensor did not fix the problem, it is either the wiring or the PCM. If there is an issue with the CHT sensor or those codes are in the PCM, the AC will not turn on.

Customer: replied 4 months ago.
I have a meter
Expert:  A. Penland replied 4 months ago.

Ok. We will need to unplug the sensor and disconnect the PCM wiring connector. Then we will need to measure the resistance (OHMS) between the sensor connector, wiring harness side and the PCM connector harness side.

Disconnect the battery also when testing for OHMS or you can damage the meter.

Place one meter lead on the (WHITE/VIOLET) wire at the CHT connector and the other lead on pin #38 on the PCM connector. Then wiggle the harness around. Your meter should read 0.0 OHMS.

Then test the (BROWN/WHITE) wire at the CHT connector and pin # ***** the same way. Below is a picture of the PCM connector so you can locate the pins.

Customer: replied 4 months ago.
Where is the PCM?
Expert:  A. Penland replied 4 months ago.

It is mounted under the dash on the passenger side behind the glove box. See below.

Customer: replied 4 months ago.
I measured the resistance and it didn't zero out, it stayed on "1"
Expert:  A. Penland replied 4 months ago.

What does the meter show when you touch both of the leads together?

Customer: replied 4 months ago.
0.00
Expert:  A. Penland replied 4 months ago.

Ok, you do have a wiring issue between the CHT sensor and the PCM. Inspect the wiring harness and follow it from the CHT sensor to the firewall to the PCM.

Also, check the connector on top of the engine. It is a rectangular connector. Below is a picture of the wiring in that connector C192. Do the same test from the CHT to that connector with it unplugged and then do the test from the other side of the connector to the PCM. This will tell us if it is on the engine or between that connector and the PCM>
They are pins #P and #R

Customer: replied 4 months ago.
ok, thanks for the help. Will try tomorrow.
Expert:  A. Penland replied 4 months ago.

Ok.

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