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Here are some step-by-step troubleshooting procedures if you're having trouble with the ECT module.
If you are having trouble programming the module, see  Troubleshooting Programming Problems.

Step 1 - Is the ECT module LED blinking? 

YES - Good, go to the next step. 

NO - If it's not blinking then the ECT module doesn't have power or the module is bad.  Since I personally test each module on an S2000 dash cluster before shipping, chances are it was good when you got it, so make sure the module has +5v power.  If you connected it to 12v, even for an instant, chances are the microprocessor in the module is blown.  If you verify +5v power is present and it still doesn't blink, contact me and we'll see what we can do about getting you a replacement.

Step 2 - Simulate a cold condition

Disconnect the ECT white wire from the ECM or EMS and temporarily connect it to the ECT module yellow wire.  This puts 5V on the white wire and simulates a very cold condition.  Turn the ignition ON but do NOT start the engine.

Does the LED blink slow, about once every 2 seconds? 

YES - Good, now check the temperature gauge in the cluster. 
NO - Either you didn't follow the steps correctly or the ECT module is bad.  Contact me.

Does the gauge indicate fully cold? (you may have to wait 20-30 seconds for it to go down to 1 bar)

YES - Good, go to the next step.
- Check the section below called "Verify the gauge wiring".

Step 3 - Simulate a hot condition

Turn the ignition OFF and disconnect the ECT module white wire from the yellow wire (where it was in the previous test).  Now connect the ECT module white wire to ground and turn the ignition back on but do NOT start the engine.  This simulates a very hot condition.

Does the LED blink fast, about 5 times a second?

YES - Good, now check the temperature gauge in the cluster. 
- Either you didn't follow the steps correctly or the ECT module is bad.  Contact me.

Does the gauge indicate fully hot? (you may have to wait 45-60 seconds for it to go up)

YES - Good, go to the next step. 
- Check the section below called "Verify the gauge wiring". 

If step 2 or 3 failed - Verify the gauge wiring

Check the connection between the ECT module green wire and the cluster (S2000 yellow/green gauge wire).  Make sure the wire going to the cluster temperature gauge has been disconnected from the ECM. If the ECU/ECM is connected to the temp gauge then the ECT module cannot control the gauge.  See wiring diagram and correct the wiring.

The output from the ECT module to the gauge is a digital signal so there's no easy way to measure or simulate it. If the wiring to the temperature gauge is correct but the gauge still does not respond properly during step 2 or 3 then there may be something wrong with the ECT module.  Contact me.

Step 4 - If you have access to a volt meter, measure the ECT Sensor Voltage

Quick test - Measure the sensor voltage as shown above when the engine is at normal operating temperatures.  The voltage should be between .4 and .6 volts.  If it is not in this range then your car/wiring/sensor is significantly different than the S2000, which is what the ECT module was designed for.  That does not mean it will never work on your car but it may require custom programming.  See this page for some measurements you can make that will help me determine how to program the ECT module to work on your car.  If your voltage is above 2 volts then custom programming will not work, as your vehicle's system is not compatible with the ECT module.

More Details - Use a digital volt meter to measure the ECT sensor voltage between the ECT module black wire and white wire.  Connect the meter as shown above and with the ignition ON read the volt meter and compare the voltage to the chart in the ECT module instructions or the text file for your version of gauge cluster.  For example, if you measure 0.620 volts go look it up in the Coolant Temperature Table in the ECT Installation Manual, where you will see that it corresponds to a temperature of 169.  Then review the ECT programming files (excerpts below) and you can see that for this sensor voltage an AP2 gauge should display 7 bars and an AP1 gauge should show 2 bars.   If the gauge reading matches what the sensor voltage and tables indicate then the ECT module is working as it should, meaning it's displaying the correct gauge reading for the voltage on the temperature sensor. 

Excerpt from AP2_AEM.TXT file

[0669] millivolts - 6th bar lights at 164 degrees
[0630] millivolts - 7th bar lights at 168 degrees
[0592] millivolts - 8th bar lights at 172 degrees
[0557] millivolts - 9th bar lights at 176 degrees

Excerpt from AP1_AEM.TXT file

[711] millivolts - 2nd bar lights at 160 degrees
[566] millivolts - 3rd bar lights at 175 degrees
[453] millivolts - 4th bar lights at 190 degrees
[364] millivolts - 5th bar lights at 205 degrees

However, if you have reason to believe the actual coolant temperature is different than what is indicated by the sensor voltage and the tables in the manual then you may have a situation where your vehicle has some kind of wiring or equipment variance that is causing the ECT voltage to be out of sync with the actual temperature.  The only way to confirm that is to use an alternate way to verify the true coolant temperature, perhaps using a separate temperature gauge or a thermometer that can be inserted into the coolant line. If you find the temperature does not match what the sensor voltage indicates then you definitely have a wiring problem that is causing the ECT sensor voltage to be incorrect.  This type of problem can occur when the ECM is changed or major wiring work is performed on the car - such as installing an EMS system.  Please read this note for more information.

Check the accuracy of the ECT module or your EMS system

Here's how you can use common resistors to verify the accuracy of your EMS or the ECT module.  The factory ECT sensor is a variable resistor that connects from the sensor input (red/white wire) to ground.  The sensor is designed so that for any given temperature the sensor will exhibit a specific resistance.  By substituting a resistor of the correct value you can cause the ECT module (or the factory ECM or the EMS system) to display any temperature reading you want.  Cool.

Note - This test assumes your EMS system uses a 2k (2000 ohms) pull-up resistor for the ECT sensor circuit.  This resistor is located inside the EMS and you may need to contact AEM to verify your version of EMS uses that resistor.  If it does, great, go ahead with this test.  If not, then the temperatures listed below will not be accurate and the pre-programmed ECT calibration values in your ECT module will not work either.  If you contact me and tell me the value of the internal pull-up resistor I can send you a calibration text file to load into your ECT module to make it display correctly.

For this test you will need to disconnect the car's ECT sensor so it doesn't interfere with the test resistor you will be using.  You can do this by either unplugging the ECT connector from the sensor where it's mounted behind the intake manifold, or you can cut the red/white sensor wire near the ECM.  Never run the engine with the ECT sensor disconnected or the substitute resistor installed.  To do so is to risk damage to the engine because the ECM/EMS won't know the real engine temperature and could supply the wrong fuel mixture.  It is safe to have the ignition ON for this test, just don't start the engine.

Step 1 - disconnect the ECT sensor (or cut the red/white sensor wire near the ECM).

Here's a photo of the rear of the engine behind the intake manifold and near the fire wall.

The ECT sensor plug is hard to reach and has a plastic tab that must be depressed in order to remove the connector.  On my car the tab was on the bottom of the connector but I don't know if that will be the case on all cars.

If the engine is hot it will be difficult to remove the connector without burning your hand on the engine, so be careful.

You might decide it's easier to cut the sensor wire.  Your choice.

Step 2 - Choose a substitute a resistor for the ECT sensor.

Here's a chart showing various "standard" resistor values and the approximate temperature for each.   For best results you should use  1% tolerance resistors (either 1/4 or 1/2 watt), which you can find at any good electronics store for 10-20 each.  Radio Shack is likely to only have 5% resistors, which will work for basic testing but obviously won't be as accurate as the 1% parts.

Pick a couple values that you want to test, no need to do them all unless you're trying to calibrate your EMS or ECT module.

ohms temp F
1000 108
680 127
470 146
430 151
330 166
270 177
220 190
150 214
120 230
100 242

Step 3 - Install the resistor according to the diagram below.  Note that if you were successful at disconnecting the ECT sensor connector in step 1 you do NOT have to cut the red/white sensor wire.  But if you left the stock ECT sensor connected you MUST cut the red/white wire so the ECT module and ECM/EMS only see your test resistor.  Just like the factory sensor, your test resistor connects from the sensor wire to ground.

Step 4 - Turn the ignition ON (reminder- do NOT start the engine) and see what the ECM/EMS or ECT module indicates.  If it's within a few degrees of the temperature shown in the chart then all is well.  If it's more than 5 or 10 degrees out then it sounds like you have a problem.  If you're using the AEM EMS system then your ECT calibration table might need tweaking.  As long as you are certain the temperatures indicated by the EMS system are correct, you can re-program the ECT module with new settings.  Just use various resistors to simulate different temperatures, record the voltage readings, and load the new values into the ECT module following the instructions in the manual.

It's also possible you have a "ground loop" problem, particularly if you see the ECT sensor voltage suddenly change when large electrical loads turn on and off (AC, fans, etc).  See this note for more information.






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