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So I finally got around to testing the sensor wires for voltage (Christmas and rain kept me from doing so). I did a base test on my battery and got 12.44v. I then connected them to the sensor plug and got two different readings. When connecting them one way I got a reading of 11.96v and then reversed the leads and got a fluctuating voltage around 12.11 volts. I know this is bad and must have a short or open circuit but I'm no electrician so any detailed advice and directions would be greatly appreciated. On a side not the Haynes manual says the wire from the sensor to the PCM is red/white, mine is green/black. Thanks for any/all help!

 
Rep Power: 518

FTFY.
Maybe paying someone who knows what they are doing would have been cheaper.

This might be a clue.
Got a scanner that can display a data list?

 
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Thanks for the suggestions. I was a mechanic for many years, didn't have to pay for any parts except the temperature sensor. Sold all my good equipment, only have a basic scanner now....scanner shows no problems...

 
Rep Power: 518

What did that mean?
What is the coolant temp shown on the datalist during the periods it will not start?
Does that reading remain stable during cranking?



When it won't start, is it missing spark?
Is it missing fuel?
Overfueling?


Have you added fuel (spray carb cleaner) to see if that makes it fire?

 
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I don't currently have a scanner that shows that much detail. When problem is present, I'm getting spark to all 4 plugs, proper fuel pressure, no over fueling . Have added injector cleaner to fuel, tried carb cleaner/starter.... Nothing
Thanks for the suggestions...

 
Rep Power: 518

You're replacing a sensor every 4-6 months that should be lasting half a lifetime. Any thought as to a reason why?


I'd strongly consider getting hold of a good one somehow.




Any engine must have

Compression
Fuel
Spark

In the correct amounts, and at the correct times.
At least one of those isn't right when yours won't run.
I'm gonna wild guess that compression isn't the problem.

 
Rep Power: 0

Hello,

I was just reading up on this sensor as I pulled the connector, jumped it, thinking it was the thermo fan switch. Car ran like crap (1991 Civic) and produced a code 6. It smelled really rich and after that and when I put it back it was fine. Looks like a sensor that couuuuuuld cause hot start problems..

Here's some testing info if you haven't seen it.


Code 6 - Coolant Temperature Sensor (ECT)
Helps determine the Pulse Width of the injectors at start-up. When this sensor starts acting-up, the engine will get hard to start, on "warm/hot starts". The wax pellet inside the sensor has gotton lazy. Sending bogus signals to the ECU, causing it to flood the engine.

When cold, it should read 2.5-4.5 volts. Also, check the IAT sensor for the same voltage, they should read close to the same. When full warmed should read .5-.6 volts. You can use a resistor with a 330 ohm 1/2 watt spec, or one from Radio Shack part# 271-1113. Start the engine and let it warm up, then kill the engine. Put the resistor in the wire connector on the harness. Start the engine, if problem goes away then replace the sensor. Use this only for temporay testing, it will cause other performance issues. Meaning the ECU will think the engine is always warmed up, when it's not.

This sensor is also known to cause hot and cold starting problems.

Temp F Volts
0 4.70
10 4.50
20 4.29
30 4.10
40 3.86
50 3.61
60 3.35
70 3.08
80 2.81
90 2.50
100 2.26

When the engine is hot, the sensor is telling the ECU that the engine is cold. Flooding occurs, due too a improper injector pulse width. Unplug the sensor if you need to start the car in a hurry. The ECU will throw a code and go into limp mode, however you will be able to drive it.

 
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So I finally got around to testing the sensor wires for voltage (Christmas and rain kept me from doing so). I did a base test on my battery and got 12.44v. I then connected them to the sensor plug and got two different readings. When connecting them one way I got a reading of 11.96v and then reversed the leads and got a fluctuating voltage around 12.11 volts. I know this is bad and must have a short or open circuit but I'm no electrician so any detailed advice and directions would be greatly appreciated. On a side not the Haynes manual says the wire from the sensor to the PCM is red/white, mine is green/black. Thanks for any/all help!

 
Rep Power: 518

If you're talking about coolant temperature sensors: There is more than one sensor, make sure you are checking the correct one.

A good scanner that can display live engine operating data in real time is a real asset when it comes to this stuff.

The Engine Coolant Temperature sensor in question has 2 wires:
Red/white and
Green/black
Both lead to the PCM

Red/white is "sensor input" to the PCM

Green/black is "sensor ground" which comes from within the PCM, and several other sensors share the same circuit. IAT and TPS share the same wire, you could jumper to either of those as a test point if you suspect a break somewhere in the harness.





When checking the 2 wires at the sensor, you need to have your voltmeter black lead in the negative port on the tester, and secured to the battery negative terminal. Leave it there.

Use the red lead to check voltages in the connector at the sensor (I like to use a THIN paper clip as the test probe, that way I don't damage the fragile terminals inside the connector.)

Key ON, engine not running: Connector unplugged: One wire should read 0 volts, the other should read 5 volts.

If the sensor is actually connected, the red/white wire should give a voltage reading that would correspond to the temperature-voltage chart....while the green/black should always give a reading of about 0 volts whenever you check it.

Make sense? HTH