HEC Instrument Cluster Diagnostics

This is a basic set of instructions for putting your 99 Mustang instrument cluster into a diagnostic mode. Doing this allows you to view the actual data being calculated by the ECC and other systems.

Written by Cornholio Productions for Mustangworld

Activating Test Mode

To enter the HEC Dealer test mode, depress and hold the instrument cluster SELECT/RESET button, turn the ignition switch to the RUN position, and then continue pressing the SELECT/RESET button (5 seconds) until tESt is displayed in the odometer. The SELECT/RESET button must be released within 3 seconds of the odometer tESt display to begin the dealer test mode.

Depress the SELECT/RESET button to advance through the following steps until dtc is displayed. Depressing the SELECT/RESET button will display any stored continuous DTCs before proceeding to the next step.

Odometer Display	Description
GAGE	Activates gauge sweep of all gauges, then displays present gauge values. Also carries out the checksum tests on ROM and EE. If the gauge sweep is inoperative, INSTALL a new instrument cluster.
All segments illuminated	Illuminates all odometer segments. If any odometer segment is inoperative INSTALL a new instrument cluster.
bulb	Illuminates all micro-controlled indicators and LEDs. Install a new indicator or LED as necessary.
r	Returns to normal operation of all micro-controlled indicators and LEDs and displays hexadecimal value for ROM level. (used when requesting assistance from the hotline). If alternating flashes for FAIL and ROM level are displayed, INSTALL a new instrument cluster.
EE	Displays the hexadecimal value for EE level (used when requesting assistance from hotline). If alternating flashes of FAIL and EE level are displayed replace instrument cluster.
dt	Displays hexadecimal coding of final manufacturing test date (used when requesting assistance from hotline).
dtc	Displays continuous DTC's in hexadecimal format. Pressing the SELECT/RESET button will display any DTCs stored before proceeding to the next step.
enG	Displays the English speed in MPH. Speedometer will indicate present speed within tolerances. Display will show 0 if input in not received. If input is invalid for one second or more, or if speed is 0.
m	Displays the metric speed data in kph. Speedometer will indicate present speed within tolerances. Display will show 0 if input in not received. If input is invalid for one second or more, or if speed is 0.
tAc	Displays the tachometer data received from the PCM via the SCP network within tolerances. Tachometer will indicate present RPM. Display will show 0 if input is no received, if input received is invalid for one second or more, or if engine RPM is 0.
FUEL	Displays the code (0-255) for the fuel sender input to the HEC. The fuel gauge will display a filtered fuel level value. This filter will keep the pointer from moving suddenly or erratically. 255 open send +/- 0 232 full stop +/- 0 215 Full mark +/- 10 178 3/4 mark +/- 8 138 1/2 mark +/- 7 93 1/4 mark +/- 5 41 E mark +/- 4 54 Low Fuel (0-59) 0-18 short (0-20 max)
OIL	Displays the code (0-250) for the oil pressure switch input to the HEC. Oil pressure gauge will indicate present oil pressure. Normal oil pressure (greater than 6psi) will display a value between 000 and 176. A low oil pressure or an inoperative engine oil pressure switch (less than 6 psi) will display a value greater than 176.
dEGC	Display of engine temperature in Degrees C input from cylinder head temperature sensor. 49 C "C" mark 60 C Normal band start 120 C Normal band end -40 C No SCP message for 5 seconds
bAtt	Displays the code (0-255) for the battery voltage input to the HEC. Battery voltage gauge will indicate present battery voltage. 93-102 6.2-9.1 volts, low voltage 115-124 8.5-10.7 volts, Normal band start 215-225 15.8-18 volts, Norm band end 230-241 16.9-19.1 volts, high voltage
rhEo	Displays the present decimal rheostat dimming input, 0-255 (used when requesting assistance from the hotline)
rhi rhS rho	Not used.
Cr	Displays the current RUN/START sense input. Display will show -h for high input with the ignition switch in the START position and -L for low input with the ignition switch in the RUN position.
PA-PE7	not used.
GAGE	Repeats the display cycle

Source: Helms 99 manual. For more information a 99 manual can be purchased from Helms see link here.

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