Digital Instruments - 1999 up SN-95
| 29 February 2004
Continuing with the late model tricks that began in January’s issue, this trick talks about the digital instrument cluster that first appeared in the 1999 model. The cluster is also called the hybrid electronic instrument cluster or HEC for short.
Nearly all displays and gauges in the instrument cluster are based on digital signals processed through various on-board computer modules. The low fuel indicator, the fuel gauge, the low coolant indicator, and the oil pressure gauge are exceptions. They each have their own hard wired sensor hookups. Gauges that appear to be analog but actually rely on digital signals include the tachometer, speedometer, temperature gauge, and the volt meter. Most of the warning lamps also rely on signals from the computers.
And you’ll be interested to hear (or maybe not) that none of the gauges are replaceable. If one of them malfunctions, the entire cluster has to be replaced. Illumination and indicator lamps are an exception; they can be replaced individually.
There are several points to be made about readout accuracy of some of the gauges. There’s also a procedure that allows you to see various digital values processed by the computer. Some of the values are fun to watch. They include vehicle speed, engine RPM, and engine temperature. The steps to access the digital information will be explained further on.
First the oil pressure gauge needs some discussion. You need to know that it doesn’t display actual pressure. It only tells you if pressure is present. The signal to the gauge turns “on” when engine oil pressure reaches 6 psi and turns “off” below that pressure. The gauge itself is calibrated to register at about mid span when a pressure switch located near the oil filter turns “on” and powers the gauge.
The volt meter or voltage gauge is similar to the oil pressure gauge in that it displays a regulated voltage. The source of the signal is the incoming “run” voltage to the HEC. So when voltage is present, the gauge will always display the same reading.
The fuel gauge displays the amount of fuel in the tank by reading a variable analog signal that comes from a tank-mounted sending unit. This makes the fuel gauge an analog dinosaur in a digital age. But the digital overseers are never very far away. The analog signal is filtered before it goes to the gauge. The purpose is to keep the gauge from showing rapid fluctuation. Nevertheless, accuracy is fairly good.
The temperature gauge displays a variable signal but it’s a digital signal sent by a computer module. The gauge is a decent indicator of actual temperature when the engine is operating in a stable mode or when change is gradual. But it’s a poor indicator when the temperature changes rapidly because Ford has seen fit to severely dampen its response to variation.
If you’d like to see digital values for some of the operating signals, it’s possible to enter what’s called the HEC Dealer Test Mode. The values will be displayed and updated, in real time, in the odometer window. The procedure for entering HEC Dealer Test Mode is:
1. Make sure the ignition key is turned “off.”
2. Depress and hold the Odometer SELECT/RESET button.
3. Continue depressing the SELECT/RESET button and turn the ignition key to the run position. Do not start the engine.
4. Continue depressing the SELECT/RESET button for about 5 seconds until the word “tESt” appears in the Odometer window.
5. Release the SELECT/RESET button within 3-seconds of when “tESt” appeared. You are now in Test Mode.
6. It’s ok to start the engine now. You’ll remain in Test Mode until you reset to normal by turning the ignition key “off.”
Now that Test Mode is active, you may want to watch the tachometer, or vehicle speed, or engine temperature or check any one of the 20 functions displayed. Step through the functions one at a time by a single press and release of the SELECT/RESET button. You can’t randomly select a function, you have to go through them in order. If you go beyond the one you wanted to watch, just keep going until it comes up the next time around. Some of the more interesting functions follow:
The first test event occurs when the word “GAGE” appears in the Odometer window. All gauges will make a full sweep to demonstrate that they are working.
The next function displays the word “bulb” and briefly illuminates all of the indicator lamps.
Step through several functions and the word “enG” will appear in the window. When you release the SELECT/RESET button you can see the vehicle speed in MPH. The next function is the letter “m” which lets you see speed in KPH.
After “m”, the word “tAc” will appear and you can watch engine RPM. Next is “FUEL” where numbers will be displayed that can be decoded from a table to show fuel level in the tank (for example, 41+4 = empty and 232+0 = full).
After “FUEL”, comes “OIL” where a numerical value in the range 0-176 is normal and a value >176 indicates low oil pressure (below 6 psi). Function “dEGC” is next. It indicates engine temperature in degrees C. Following “dEGC”, is function “bAtt” where numbers in the range 0-255 can be decoded from a table to indicate battery voltage.
The HEC can be an interesting toy to play with. But sometimes it can be intoxicating and distract your attention from the road. Be careful if you use it while you’re driving. I have the tables if anyone sees values that they want to decode.