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Old 09-04-2019, 10:41 PM   #1
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Strange, frustrating Cylinder head temparature sensor problems

Hi, everyone!

Alright, so my car is an '03 with the 2.0 Zetec. I had big problems getting her to start+self acceleration. A check engine light ended up being P1289- Cylinder head temperature sensor signal greater than self test range. Thinking it is simply a bad CHT, I ordered a Standard Motors CHT and had it changed out. It didn't work.

Based on advice from my mechanic, I had the CHT changed out once again- this time for a 'used' sensor salvaged from another vehicle (common practice in my country as new parts are hard to come by). This didn't work either, and neither did a third salvaged CHT sensor that replaced it. My mechanic now recommends I order another sensor from out of the country; however, I am beginning to think it might be less about the sensor. This is because all 3 sensors failed in a very similiar pattern. I have summarized them below:

1) The temp gauge crawls up to the 'cold' mark on starting the car cold; but then after about 5 seconds it 'bottoms out,' to the point at which it stays when the car is not running. If the car is later turned off, then on at this point, its starts relatively easily, however I notice the gauge needle would go to its normal point (either the middle or close, depending on how long the engine has run) then bottom out again. When I reset the ECU, the check engine light comes on at the same time the gauge 'bottoms out'

2) Then, after about 20 or so minutes of driving , it suddenly bounces back to the 'cold' mark. This is accompanied by a jump in RPMs to about 1300 (it's usually at 700-800rpms). The car also self accelerates at this point and is extremely difficult to start if turned off at this point- it eventually would sputter to a start - with alot of black fumes and the accelerator firmly welded to the floor.

3) After about 10 more minutes, the temp gauge suddenly heads to its normal point at the center and rpms drop. The car drives normally and would start very easily at this point. However, it at times goes to the cold point, and then returns to normal.

From the little research I have done, I hear there is another resistor in tandem with the CHT. Could that be the source of my problems? I am basically clueless at this point!

This problem has gotten me to my wits end and is slowly eating away at my sanity ( not to mention my wallet- the old girl has become HORRIBLY thirsty).

I would appreciate any help to get my car back to normal!

Cheers!



Last edited by Billy187; 09-04-2019 at 10:50 PM. Reason: left out a detail
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Old 09-04-2019, 11:46 PM   #2
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Hello Billy in Ghana.

I rarely offer good diagnostic advise, but I do try and help, -mostly just with my questions, that ultimately do help.

My Zetec experience & knowledge is near Zero. I will hope that others more Zetec experienced than I will come forward and help you more.

My first thought is (I think) that CHT sensor comes in different variants (sizes) that sometimes trip-up people when replacing it. People have replaced that sensor, only to later find out the sensor they installed was the wrong size/wrong type. I highly doubt you need a CHT from the USA. We need a "Zetec person" to add comments about this.

No, I do not think there is an additional resistor in the circuit outside of the CHT sensor and the PCM. However, the wiring and the electrical connectors involved can & will act like an electrical resistor when defective; and can also cause problems intermittently.

I do believe your CHT wiring is suspect defective. You (or your mechanic) should do an extensive and very careful wiring test of the CHT wires between the sensor and the PCM. Wiring is not "good" because of a simple or rushed "ohms check".

The PDF link below is for 2002, but is highly reliable for 2000-2004 European (and similar Asian, African, Australian car markets) and is not for the North American markets. It is a wire diagram book from Ford. This book has been shared online for many years, and it sometimes causes problems for people who use it for a North American Focus. After you review the table of contents, I would recommend you start at page 303-03-00 (-01).
https://drive.google.com/file/d/0Bwo...ew?usp=sharing

Good Luck
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Last edited by Marde; 09-04-2019 at 11:59 PM.
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Old 09-05-2019, 04:28 AM   #3
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Quote:
Originally Posted by Marde View Post
Hello Billy in Ghana.

I rarely offer good diagnostic advise, but I do try and help, -mostly just with my questions, that ultimately do help.

My Zetec experience & knowledge is near Zero. I will hope that others more Zetec experienced than I will come forward and help you more.

My first thought is (I think) that CHT sensor comes in different variants (sizes) that sometimes trip-up people when replacing it. People have replaced that sensor, only to later find out the sensor they installed was the wrong size/wrong type. I highly doubt you need a CHT from the USA. We need a "Zetec person" to add comments about this.

No, I do not think there is an additional resistor in the circuit outside of the CHT sensor and the PCM. However, the wiring and the electrical connectors involved can & will act like an electrical resistor when defective; and can also cause problems intermittently.

I do believe your CHT wiring is suspect defective. You (or your mechanic) should do an extensive and very careful wiring test of the CHT wires between the sensor and the PCM. Wiring is not "good" because of a simple or rushed "ohms check".

The PDF link below is for 2002, but is highly reliable for 2000-2004 European (and similar Asian, African, Australian car markets) and is not for the North American markets. It is a wire diagram book from Ford. This book has been shared online for many years, and it sometimes causes problems for people who use it for a North American Focus. After you review the table of contents, I would recommend you start at page 303-03-00 (-01).
https://drive.google.com/file/d/0Bwo...ew?usp=sharing

Good Luck
Thanks so much for the reply! Though I'm in Ghana, my Focus was imported from Canada (its the SE) and would be more in line with those from the US.

However, on looking at your reply I decided to physically check the connecter (harness) leading to the CHT and noticed a connection covered by electrical tape (probably from the former owner, or probably from my mechanic). I will try and attach the picture below.

Do you think it might be a possible suspect area?

Thanks!
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Old 09-05-2019, 05:12 AM   #4
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Quote:
Originally Posted by Billy187 View Post
...However, on looking at your reply I decided to physically check the connecter (harness) leading to the CHT and noticed a connection covered by electrical tape (probably from the former owner, or probably from my mechanic). I will try and attach the picture below.

Do you think it might be a possible suspect area?

Thanks!
The picture did attach, I see it. Good job mate.

The first answer is yes, and the second answer is yes. That electrical tape is likely hiding a bad/poor/shit electrical connection to the CHT sensor.
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Old 09-05-2019, 04:30 PM   #5
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Quote:
Originally Posted by Marde View Post
The picture did attach, I see it. Good job mate.

The first answer is yes, and the second answer is yes. That electrical tape is likely hiding a bad/poor/shit electrical connection to the CHT sensor.
Alright, so I decided to tear open the electrical tape as soon as I got home from work- lo and behold, the wires were literally hanging on by strands!, I fixed them up, crossed my fingers and started the old girl....and she RUNS!! YES!! No check engine lights, and temp gauge slowly crawled up as the car idled! I have not driven the car, but then I bet its gonna drive much better now. Its amazing how a few frayed wires can bring down an entire car! Even more amazing is how no mechanic I took this to figured it out! (heck, one even recommended I change my head gasket!)

To say I'm overjoyed with the outcome would be an understatement. Marde, you are a legend among men, I really owe one on this! Perhaps, a cold one if you do happen to pass through Ghana?
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Old 09-06-2019, 01:13 AM   #6
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It is a great day when the fix is simple. Good job Billy.

Thank you for the ridiculous complement. Many others here could have & would have given you the same or similar advise. This is FF, and we have many different people, experiences and talents. Team work, -works.

Cheers!
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