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Wiring Diagram (only) AP1 Full Manual AP2 Full Manual
Here are some troubleshooting procedures if you're having trouble with the ECT module.
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.
Test the ECT input circuitry
Disconnect the ECT white wire from the ECM or EMS input and temporarily connect it to the ECT module yellow wire. Then turn the ignition ON but do NOT start the engine. Putting 5 volts on the white wire simulates a very cold condition causing the LED on the module to blink slowly, about once every 2 seconds.
Next, turn the ignition OFF and disconnect the ECT module white wire from the yellow wire. If you cut the yellow wire for the previous test be sure to insulate it so it doesn't short to anything. Now connect the ECT module white wire to ground. This simulates a very hot condition and when you turn the ignition back ON the LED should start blinking fast, about 5 blinks a second.
YES the LED blinks as described above - Good, that means the ECT module is working so go to the next step.
NO the LED did not blink as described - Either you didn't follow the steps correctly or the ECT module is bad. Contact me.
Verify the gauge operates
Check the connection between the ECT module green wire and the yellow/green gauge wire. Make sure the yellow/green has been disconnected from the ECM and the end that runs towards the hood release (to instrument cluster) is connected to the ECT module green wire. If it's still connected to the ECM then the ECT module cannot control the gauge. See wiring diagram and correct the wiring.
The output from the ECT module that drives the gauge is a digital signal so there's no easy way to measure or simulate it. But if you repeat the previous test of connecting the white wire to the yellow wire you should see the temperature gauge indicate full cold. If you then connect the white wire to ground this will simulate a very hot condition causing the dash gauge to light up all the segments. It might take a minute or more for the gauge to light all the segments but they should all eventually light up.
YES the gauge operated as described - Good, re-connect the ECT white wire to the red/white sensor wire and go on to the next test.
NO the gauge didn't operate correctly - Either the ECT module is
not wired to the gauge correctly or the ECT module is bad.
Contact me.
Measure the ECT Sensor Voltage
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 and have an AP2 gauge, the gauge should display 7 bars because .620 volts (620 millivolts) is between the 7th and 8th bar as shown below. For an AP1 gauge you should see 2 bars on the gauge.
|
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 |
Excerpt from AP1_AEM.TXT file [711] millivolts - 2nd bar lights at 160
degrees |
If the gauge reads correctly then the ECT module is working as it should but you may need to re-program it for your particular installation. If you look up the .620 volt reading in the ECT manual you will find that it corresponds to a coolant temperature of 173° for an AEM EMS system. If that is not the actual coolant temperature then you most likely have some kind of wiring or equipment variance that is causing the ECT voltage to be out of sync with the actual temperature. In this case you may need to find an alternative way to verify the true coolant temperature (separate gauge?) and make several voltage/temperature measurements over as wide a range as possible and use that data to re-program the ECT module.
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. |
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| 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. |
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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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