ECT Help    ECT Home    AP1 Details    AP2 Details    Buy Here    Install Info

Using the ECT Module on vehicles other than a stock S2000

The ECT module was specifically designed for the S2000 but it should work on most Honda vehicles if the coolant temperature sensors are similar.  The information below should help you determine if that's the case, and help you calibrate the ECT module for best results.  If you are putting the S2000 instrument cluster in a non-Honda vehicle or just want to guarantee that the temperature gauge will work correctly you should consider installing a stock S2000 temperature sender just for the temperature gauge.  See here for details.

First, some basics

The ECT module works by measuring the voltage on the engine coolant temperature (ECT) sensor wire and generating the correct digital signal to drive the temperature gauge.  The ECT sensor voltage varies with temperature, with higher voltages for lower temperatures and lower voltages for higher temperatures.  The voltage generated for a specific temperature will always be the same, as long as the same sensor and ECM are used. 

Bear in mind the voltages we're talking about are very low - less than one volt.  In some cases a voltage change of 0.1 volt corresponds to a temperature change of 30° or more, so you can see that having the correct sensor voltage is critical to proper operation of the ECT module, and hence, the temperature gauge.  That's why the voltage/temperature data for the ECT Module has been determined by actual measurements of the voltage and engine coolant temperature with precision test equipment over a wide range of temperatures.  It's this "chart" of temperature and voltage measurements that is programmed into the ECT module so it knows how many gauge segments to light up for each specific sensor voltage.

Unfortunately, not all cars use the same sensor or ECM, and for each combination of sensor and ECM there is a specific, though different, relationship between the temperature and the sensor voltage.  For example, a stock S2000 will have a sensor voltage of .350 volts at 235°F, which would indicate the engine is severely overheated.  But that same voltage on an S2000 with the AEM EMS (replacement ECM) correlates to a temperature of 208°, well within the normal temperature range. Note that in both cases the engine is the same and the coolant temperature sensor is the same - all that changed was the ECM (from stock to after-market).  The point is that the sensor voltage can be affected by any change from the stock S2000 configuration, and since the S2000 sensor voltage is the basis for the ECT module programming, if the voltage varies from the "standard" then the gauge display will not be accurate.

Because there is a huge number of combinations of different sensors and ECMs it's impossible to build all of that data into one device.  That's why the ECT Module is designed to allow the end user to reprogram it as needed, to match the individual characteristics of his vehicle, much like an engine tuner will tweak an after-market ECM to match the specific combination of engine components for that installation.

Now that you have some basic information, let's get more specific. 
Gauge Clusters - Which one are you using?

There are two versions of the S2000 gauge cluster, named AP1 and AP2.  AP1 refers to years 2000 to 2003 and AP2 is years 2004 and 2005.  You must use the correct ECT module for the cluster you have.  Using the wrong ECT module will cause the gauge to read incorrectly, and this cannot be fixed by loading new values into the module - you will have to change the ECT module.

AP1 Clusters (S2000 years 2000-2003) Tach redline is at 8900 rpm

The AP1 temperature gauge has 7 segments arranged in a horizontal bar graph.  The first segment is not active, meaning it's always on no matter what the coolant temperature.  The next 5 segments are yellow and the last one (#6) is red, and these are the segments that will progressively light up to indicate coolant temperature.

To make the best use of the limited number of gauge segments I designed the AP1 module to have a lower temperature limit of about 160°F when used in an S2000, which corresponds to an ECT sensor voltage of 0.978 volts.  In actuality the AP1 ECT module can work with voltages up to .999 volts, which is a tad below 160°.  As the temperature increases the voltage drops, so this module can display temperatures of 160° or above (on an S2000), which correlates to sensor voltages between 0 and 0.999 volts.  If you are using an AP1 cluster and your ECT sensor voltage is in this range for normal engine temperatures then the ECT module will work in your car, though it may require re-calibration.

AP2 clusters (S2000 years 2004 and 2005) Tach redline is at 8000 rpm

The AP2 temperature gauge has 20 segments arranged in a 180° circular sweep.  The first segment is not active, meaning it's always on no matter what the coolant temperature.  The next 19 segments are the active segments that will progressively light up to indicate increasing coolant temperature.

Since this gauge has more resolution (more segments) I designed the AP2 module with a lower temperature limit of about 110°F (when used in an S2000), which corresponds to an ECT sensor voltage of 1.944 volts.  As with the AP1 module, higher temperatures are indicated by lower voltages, so this module can display temperatures of 110° or above (on an S2000). 

Note - the ECT Module will NOT work on clusters from years 2006 and up.  These clusters use the S2000 data bus to operate the temperature gauge and they are not compatible with the ECT Module.

Testing procedure to see if your car will work with the ECT module

The best way to determine if your car will work with the ECT module is to measure the voltage on the ECT sensor wire where it enters the ECM.  Refer to the sensor voltage/temperature chart in the ECT Module Installation manual (AP1 or AP2) to be sure your measured voltage matches what the module is expecting.  You should use a digital volt meter for this test, connected between the ECT sensor wire and ground, preferably the sensor ground wire at the ECM (for best accuracy).  See this diagram showing how to make this measurement.

A cold engine will probably read 3 to 4 volts from the sensor wire to ground, which is too high to be measured by the ECT module.  But we don't really care because the engine is dead cold - all we care about is the readings we get when it starts warming up.  As the engine warms and the coolant temperature rises, the ECT voltage will drop, and if it drops down to around 0.5 volts when the engine is fully warmed up then it's in the correct range and you should be able to reprogram the ECT module to work in your car.  If your sensor voltage is significantly above .5 volts you may still be able to use the ECT module but it may require adding some external resistors to "scale" the ECT voltage.  Once you have all your voltage/temperature measurements contact me for information on how to scale the sensor voltage.

In order for the ECT module to work "out-of-the-box" with no programming changes your measured sensor voltage will need to be within .01 volts of the values listed in the Installation Manual charts for the range of coolant temperatures you expect to see.  If you cannot determine your actual coolant temperature and confirm that the sensor voltage is correct then there is no way to predict if the ECT module, as shipped, will work properly in your car.   

Want to guarantee the ECT module will work?  - Install a stock S2000 ECT sensor as a dedicated temperature sensor and wire it to the ECT module.  I don't have a diagram yet but it's simple to wire.  Connect a 1500 ohm resistor between the ECT module white and yellow wires.  Then connect one sensor wire to the ECT module black wire and the other sensor wire to the ECT module white wire .  This will mimic the S2000 system and you can use the "stock" version of the ECT Module to operate your temperature gauge without the need for taking voltage measurements or re-calibrating the module.  If you intend to do this send me an email BEFORE you order the ECT module and I'll include the 1500 ohm resistor in your order.  You're on your own to find a suitable place to install the coolant temperature sensor.

Procedure for calibrating the ECT module for your car.  

Tools needed -  Digital volt meter and a coolant temperature gauge - this can be either an ODB-II reader, AEM EMS system or other after-market ECM with built-in temperature gauge, or a standard coolant temperature gauge (standard gauge will not be as accurate).  Once you are finished recording the voltage/temperature readings you will need a PC with a standard serial port to load the new calibration values into the ECT module.  See this diagram to see where to connect your meter to take the measurements.  Bear in mind this photo is

You should start with a cold engine and connect the digital volt meter between the ECT sensor wire and ground.  Turn ON the ignition but don't start the car, then take a voltage reading on the ECT sensor and note the coolant temperature on the OBD-II output, the EMS system, or your external temperature gauge.  Now start the car and monitor the temperature as the engine warms up.  I suggest you record the ECT voltage every 5 or 10 degrees as the car warms up.  The more measurements you take the easier it will be to accurately program the ECT module.  And, since the voltage/temperature relationship is not a constant ratio it's hard to predict what the voltage will be for a given temperature, so the more readings you get at the hot end of the scale the better.

Once you have your list of temperatures and voltages, decide what temperature range you want the S2000 gauge to display and start selecting the temperature you want each gauge "bar" to represent.  Write down the corresponding voltage for each of these temperatures. 

Using the instructions in the ECT manual, edit the standard programming file, replacing the old voltage values with your new ones.  Save the file with a new name, then follow the manual instructions to load the new file into the ECT module.

Special note to AEM EMS owners:

Some customers have had difficulty getting the gauge to display properly on AEM EMS systems.  I know of at least two cases where, after some troubleshooting, customers verified the voltage on the ECT sensor wire would change when other electrical loads turned on and off.  Sometimes the change was only 50 or 60 millivolts, sometimes several hundred millivolts.  In particular the radiator fan and AC system seem to cause the ECT voltage to fluctuate, and that of course makes the gauge display fluctuate too.

These symptoms are classic examples of a "ground loop".  Ground loops occur when current for one electrical circuit inadvertently flows through the ground leg of another circuit.  Here's an extreme example (if you have an S2000): pull the fuse for one of your HID headlights (low beam), then turn ON the low beam lights and check out the front of the car.  Not what you expected, huh? 

You probably figured one light would work and the other would remain off.  But in fact you will see one light come on normally, the other HID will flicker, and both high beams will be lit dimly.  This is how a ground loop works.  Power from the working low beam circuit back-flows through the high beam filaments and makes it's way to the low beam with the missing fuse.  Because current passes through both high beams and the HID (one big series circuit) they each get less than 12v, causing the high beams to glow faintly and the HID to flicker.  Cool.

With the ECT sensor, it's a similar effect.  If the sensor ground wiring is not exactly perfect, ground current for other devices will flow in the sensor ground wire, causing a voltage change that the ECT module (and the EMS too) will interpret as a different temperature.  How does ground current get into the sensor ground?  Think about it - how does ground current get anywhere in a car?  It flows through the chassis.  We think of the chassis as "one big ground lug" but in fact it's "one big resistor".  OK, it's a resistor with very low resistance, but when you pass a large current through even a low-ohm resistor you will get a noticeable voltage drop.

So the question is - did you move ANY ground wires in your car?  Did you remove or re-route any wiring to the engine block?  Did you move a ground lug or terminal from one bolt to another one "close by"? Did you move the ECM and use a new ground for it? Did you ground the ECT module anywhere other than directly at the ECM or at the ECM sensor ground?

Since the ECT sensor operates with very small voltages, even that "close by" ground bolt might not be close enough to maintain the ground integrity of the sensor wiring.  If there's only 1/100 of an ohm resistance between the two chassis points (original ground point and your new one), the radiator fan current (30-40 amps) could cause 300-400 millivolts change in the ECT voltage.  That 0.3 volts won't affect the radiator fan, but will surely screw up the ECT reading!

The bottom line: If you have ECT gauge problems, the first thing to do is put a meter on the ECT sensor wire and measure the voltage.  Look it up in the voltage/temperature table in the manual to see if it's in the range it should be.  Turn everything electrical ON and OFF and see if the sensor voltage changes.  It shouldn't change by more than a few millivolts no matter what is turned ON or OFF.  If it makes any sudden changes with electrical activity, then you've got a ground loop.

Copyright 2005 by Modifry Products, LLC all rights reserved.
Modifry and the "squiggly arrows" design are trademarks of Modifry Products, LLC. 
AEM and AEM EMS are trademarks of AEM Performance Electronics. 
Neither Modifry Products, LLC nor Modifry.com are sponsored, endorsed, affiliated or authorized by AEM.