Car question - Cylinder Heat Temperature Sensor "out of Self-Test Range"

[Lone_RT_rider]

I originally posted this on a Focus specific website, but I thought posting it here was worth a shot. Thanks for any input you might have.

 

We have a 2004 Ford Focus SE (16V I think) that is giving me an OBD2 code of Temperature Sensor out of Self-Test Range (P1288). When I go to search for a Cylinder Head Temp sensor (CHT) on any of the auto parts store sites, they do no list this part for the 2004 model year. The part is however listed for 00-02 cars as an SMP PN of TS431.

 

There is however a coolant temp sensor listed with a PN of TX90 for the 2004 Focus SE. Is it possible that the CHT was deleted and the Coolant Temp sensor is doubling for this input in the ECU? When reading the inputs on the OBD2 for the ECU the temps for both the CHT and the coolant temp sensor are listed, but read virtually identical in values. What gives? Any ideas?

 

Shawn

[big-t]

Shawn,

the Focuses run vary high coolant temps,235 before the low speed fan comes on and the high speed comes on at 245,so I think they will only have a CHT sensor as its pretty critical on this vehicle.I can't get to my tech sources right now to check for sure.

 

 

that is giving me an OBD2 code of Temperature Sensor out of Self-Test Range (P1288).

 

 

Codes like this one can be misleading,it might indicate a sensor problem or its also possible the engine was hotter or colder than expected when it ran the self test.Without an explaination of the what it takes to set the code,its really just a guessing game.

 

A couple of other tidbits....I believe there are some TSBs on the cooling system/CHT on that car.

 

I have seen them melt the plastic thermostat housing and its extremely critical to get ever last bit of air bled out of the cooling system.(I believe there is a specific way to accomplish this)

 

Don't rely on the local auto parts to give you the right stuff on late model cars They can be a PITA,just in case you haven't noticed.

 

 

I can go by the store tomorrow and look up anything you need,let me know.

[Lone_RT_rider]

I have seen them melt the plastic thermostat housing and its extremely critical to get ever last bit of air bled out of the cooling system.(I believe there is a specific way to accomplish this)

 

I purchased a Hanes manual tonight (I know, this could be dangerous ). One of the things it mentioned is that the thermostat has an air-bleed hole that is located at a point that allows it, and requires it to be located at 12 o'clock so that the air bleed can effectively happen. I have replaced the thermostat once, but I can't recall if I did this correctly. I will be checking that tomorrow.

 

There is another condition I forgot to mention that I saw. When the car was idling for a good bit of time, I observed the temp guage do some wide and eratic sweeps (30 degree range) while at exactly the same time the engine RPM raised )approximately an additional 1000-2000 rpm. Once the fluctiation in the temp guage stopped, the rpm dropped back down to normal. But, at the same time the temp guage dropped back down to nothing.

 

While thumbing through the Hanes manual, I noticed that the ECT is just below the ignition coil-pack (coil). A while back I allowed my workplace to used the Focus as a testbed for an aftermarket coil they were devleoping at the time. I am curious at this point if they might have bumped or upset the connector on the ECT. I will be checking that tomorrow as well.

 

Todd.... If you can find the TSB's on this I would greatly appreciate it. I am pretty sure you have my cell, but I will PM you with it just in case. Thanks so much for responding

 

Shawn

[T__]

Shawn, I know virtually nothing about the Ford engine electronics as I work for a different motor company but they do operate basically the same as the one I am familiar with..

 

With the above being said make darn sure you don’t have a spark plug wire or coil wire or any high energy ignition component running on or near the CHT or CTS wiring or sensor.. Just a little high energy RFI can drive that sensor circuit crazy & force all kinds of error codes..

 

Twisty

[4wheeldog]

I think you may be a little off on your diagnosis. Most O2 sensors and catalytic convertors require the cat to be hot enough to work. There is often a sensor that needs to be up to temp so that the system can go closed loop. If the mixture is too lean, the cat never warms up.

The first place I would look is the fine wire MAS sensor ahead of the air filter. If it has some dirt baked on it, your mixture will be lean and give you the code you have. You can replace it for big $$$ or, if you are really careful, you can clean it with electronic parts cleaner. DAMHIK. Good Luck!