Check Engine/Engine Head Temp Sensor
Thread Starter
Instructor
Joined: Jul 2003
Posts: 234
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From: Los Angeles, California
Check Engine/Engine Head Temp Sensor
I just had the check engine light go on, which when checked by the dealer showed two codes--AC open circuit and engine head temp sensor. The AC was just because I forgot to reconnect the AC the last time I pulled it off. The other code is more concerning. I have several questions which if anyone knows the answer to would be very helpful...
1) Where are the fault codes stored? Are they in the DME or somewhere else? I just replaced the engine and so I'd like to be able to rule out the code being from the previous engine, which had a number of problems and ran a little hot right before it died. If it is in the DME, then I know the code is from the new engine.
2) The engine has a really hard time starting when it is cold. It's fine once it's warm, but when the car is cold the car refuses to start. Could this be connected to the engine head temp sensor, maybe not correctly reading the cold temperature. I understand the engine head temp sensor is used by the DME to set the fuel/air mixture.
Thanks.
1) Where are the fault codes stored? Are they in the DME or somewhere else? I just replaced the engine and so I'd like to be able to rule out the code being from the previous engine, which had a number of problems and ran a little hot right before it died. If it is in the DME, then I know the code is from the new engine.
2) The engine has a really hard time starting when it is cold. It's fine once it's warm, but when the car is cold the car refuses to start. Could this be connected to the engine head temp sensor, maybe not correctly reading the cold temperature. I understand the engine head temp sensor is used by the DME to set the fuel/air mixture.
Thanks.
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From: Chino hills, CA
Harry,
The error code is stored in the DME.
The function of the engine teperature sensor (head temp sensor) is to be used like a coolant temperature sensor (in a water cooled car) to determine if the engine is cold and to allow the DME to richen the fuel/air mixture to help with the cold starting process.
From your symptom sounds like either the engine temperature sensor (head temp sensor) is defective or is not connected.
The error code you should have received from a bad engine temperature sensor should be error code 14, and measurement method to determine if the sensor is defective is ohm reading.
A quick test from the wiring loom connector of the DME unit (unplug it from DME unit) can determine which is which.
Connect a voltmeter which is set on ohm reading to pin number 45 and 14 of the wiring loom. Below are a list of values you should see if the temperature sensor is working properly.
0C = 4.4 - 6.8 k ohm
15-30C = 1.4 - 3.6 k ohm
40C = 1 -1.3 k ohm
80C = 250 - 390 ohm
100C = 160 - 210 ohm
The sensor is located on the cylinder head of the 3rd cylinder.
The error code is stored in the DME.
The function of the engine teperature sensor (head temp sensor) is to be used like a coolant temperature sensor (in a water cooled car) to determine if the engine is cold and to allow the DME to richen the fuel/air mixture to help with the cold starting process.
From your symptom sounds like either the engine temperature sensor (head temp sensor) is defective or is not connected.
The error code you should have received from a bad engine temperature sensor should be error code 14, and measurement method to determine if the sensor is defective is ohm reading.
A quick test from the wiring loom connector of the DME unit (unplug it from DME unit) can determine which is which.
Connect a voltmeter which is set on ohm reading to pin number 45 and 14 of the wiring loom. Below are a list of values you should see if the temperature sensor is working properly.
0C = 4.4 - 6.8 k ohm
15-30C = 1.4 - 3.6 k ohm
40C = 1 -1.3 k ohm
80C = 250 - 390 ohm
100C = 160 - 210 ohm
The sensor is located on the cylinder head of the 3rd cylinder.
Thread Starter
Instructor
Joined: Jul 2003
Posts: 234
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From: Los Angeles, California
Robin:
I can't thank you enough. I did the test you suggested and it turned out that the head temp sensor was dead--open circuit. I did the check at the white plug at the back left of the engine bay. I tried to do it at the wiring harness loom, but pin 14 on my car turned out not to have anything connected to it. Somehow, the wiring on my car is a little different.
Anyway, replaced the sensor tonight--what a pain that was--and tried to start the car (it was stone cold, having sat for a few days). It fired up immediately and very strongly. Problem appears to be solved, and I don't think that check engine light will be coming back either--at least not for this reason.
Harry
I can't thank you enough. I did the test you suggested and it turned out that the head temp sensor was dead--open circuit. I did the check at the white plug at the back left of the engine bay. I tried to do it at the wiring harness loom, but pin 14 on my car turned out not to have anything connected to it. Somehow, the wiring on my car is a little different.
Anyway, replaced the sensor tonight--what a pain that was--and tried to start the car (it was stone cold, having sat for a few days). It fired up immediately and very strongly. Problem appears to be solved, and I don't think that check engine light will be coming back either--at least not for this reason.
Harry
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Joined: May 2002
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From: Tampa
Harry,
You probably did not have the 'tool'. I modeled this after the official Porsche tool. Craftsman wrench (14mm on the one side). A little slot so it fits over the wire, and a little grinding on the outside and it fits like a dream between the head and the sensor. You can change the sensor in just a couple of minutes with this..
Sorry for the focus. Forgot to reset the auto focus on the camera...
You probably did not have the 'tool'. I modeled this after the official Porsche tool. Craftsman wrench (14mm on the one side). A little slot so it fits over the wire, and a little grinding on the outside and it fits like a dream between the head and the sensor. You can change the sensor in just a couple of minutes with this..
Sorry for the focus. Forgot to reset the auto focus on the camera...
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I wonder if the head temp sensor is gonna be a more common failure in the near future???????????
Thats weird, on my 911th post, I was talking about cyl head temp sensors....ala 84-89 911 common problem....
I wonder if the head temp sensor is gonna be a more common failure in the near future???????????
Thats weird, on my 911th post, I was talking about cyl head temp sensors....ala 84-89 911 common problem....
Thread Starter
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Joined: Jul 2003
Posts: 234
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From: Los Angeles, California
Bob:
No, I didn't have "the tool". I'll have to remember that one--would have saved me a lot of time. I cut the wire off the old one and then put a socket over it. Was a very tight fit and took a lot of time to eventually get it out. The new one I just put finger-tight. There is no way it is working its way out given that the wire resists twisting of the sensor.
I really appreciate the tip.
Harry
No, I didn't have "the tool". I'll have to remember that one--would have saved me a lot of time. I cut the wire off the old one and then put a socket over it. Was a very tight fit and took a lot of time to eventually get it out. The new one I just put finger-tight. There is no way it is working its way out given that the wire resists twisting of the sensor.
I really appreciate the tip.
Harry
