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Discussion Starter #1
I have a 2003 2.0 ZX3 Zetec Focus. Starting a couple of weeks ago my car will sometimes self accelerate when I let of the gas. Sometimes when it shifts gears it will also jerk a lot. I have noticed the temp stays low for a while much longer than it used to. All of the problems seem to amplify when I run the AC so I have not been running it. I got two codes yesterday P1289: Unknown and P0128 Coolant Thermostat. Some background replacements are I had my Thermostat replaced roughly 6 months ago because it was leaking and about a month ago I replaced the Head Temperature Sensor hoping that would help my stall out at start issue I've had for years. Anyone have some tips for checking health of thermostat and what else might cause these codes?
 

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DTC P0606
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P1289 - Cylinder Head Temperature (CHT) Sensor Circuit High Input
Indicates a CHT sensor circuit malfunction (open).
Open circuit in CHT harness
Damaged CHT sensor
Improper harness connection

Recheck your work on the temp sensor. The cylinder head temp is not being read properly due to an open circuit - loose, crimped or broken wire/connector possibly - so it would not be surprising if the car ran as if it were cold all the time.

Stalling or failing to idle properly can be due to a number of things but the temp sensor isn't likely to be the root cause.
 

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Discussion Starter #3
Thanks for the help. I was afraid it was pointing to that. That was the hardest thing I have done with car maintenance to date. That alternator has only one way it likes to go in and it's very challenging.

Do you think the other code about the thermostat is just an effect of a bad CHT sensor?

On my way to work today it read cold for about 15 minutes then it finally started to settle out at the middle like it's supposed to. While it is cold is when it runs a bit ruff, it runs much worse if I try to run the AC.
 

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Grey Friar
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Does the car idle rough, or unsteady rpms at idle? Does it balk or bog at any time?
 

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Discussion Starter #5
The idle seems to be fine, except it's at around 1200. It does bog and choke up sometimes when I start driving. Especially if I have the AC on.
 

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If the PCM thinks the engine is colder then it is then that will cause over fueling problems(right?). A friend had his car idling high and not starting when it was warm, had him check a few things on torque and his coolant temp sensor was reading -16... Replaced it and no problems since. This is the same thing correct?
 

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Discussion Starter #7
A bit of an update. Yesterday when I got off work it was hot out and my temp gauge settled at the middle and it drove fine. I went to the mechanic and it still had the CHT code. He cleared it and it still came in. He noticed there was some oil looking residue on the CHT connector and he sprayed it off with some electrical cleaner. The code cleared.

This morning the gauge was bottomed out my whole way to work and it's RPM's were high. So high that it self accelerates when I let off the gas. Some times the gauge even went bellow the bottomed out level.

I guess this is what I get for buying the advance auto part vs the motorcraft. Does anyone have some other thing I could test before I go back through that battle to replace the little sensor?
 

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Thanks for the help. I was afraid it was pointing to that. That was the hardest thing I have done with car maintenance to date. That alternator has only one way it likes to go in and it's very challenging.

Do you think the other code about the thermostat is just an effect of a bad CHT sensor?

On my way to work today it read cold for about 15 minutes then it finally started to settle out at the middle like it's supposed to. While it is cold is when it runs a bit ruff, it runs much worse if I try to run the AC.
I am curious what was so hard about changing the CHT sensor? It is literally a 3 minute job. You may have damaged the connector as stated above. Instead of throwing parts at it, fix the work you have done incorrectly.
 

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In order to change the sensor out it is required to remove the alternator. It's difficult to get in and out. It has worked fine for 3 months.
Apologies. I was reading too many posts and thought you had a Duratec. I think you should replace the connector going to the CHT sensor first.
 

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Put an Ohm meter on the CHT sensor. Start the car and see if the resistance through the CHT sensor changes. Easiest way to see if the CHT sensor has failed.
 

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The other code, P0128, is for engine not reaching operating temperature. Often it means a stuck-open thermostat, but not always. If the CHT is getting wonky info, then you'd get that code regardless of what the real temperature is.

You can pick up a pyrometer for about $20 that you just point at the engine to see what the real temperature is, and compare that to what range the sensor is reporting. I find it a handy little tool for anything heat-related, though originally I bought it for checking temps across the treads on my race tires.
 

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My apologies for reviving an old thread, but it seems i have similiar issues. I also had a similiar code P1289, with the characteristic self-acceleration. It was also a handful to start and when it finally does start, its with lots of black/ blue smoke and extremely high rpms. I have since changed the CHT out for one made by Standard- which worked for a few days before the ominous P1289 popped up again. I then changed that out for two (used) sensors; with no sucess. Is there some other component i should focus on? How would I know its my wiring? Thanks so much!
 
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