Seems pretty often someone asks about using the digital trip meter as a tach.

Here is how you do it:

To enter the 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.

Start the engine with the odometer in test mode.

Depress the SELECT/RESET button to advance through the following steps:

Here is what you get:

GAGE: Activates gauge sweep of all gauges, then displays present gauge values.

r: Returns to normal operation of all micro-controlled indicators and LEDs.

EE: Displays the hexadecimal value for EE level.

dt: Displays hexadecimal coding of final manufacturing test date.

dtc: Displays continuous DTC's in hexadecimal format.

enG: Displays the English speed in MPH. Speedometer will indicate present speed within tolerances.

m: Displays the metric speed data in kph. Speedometer will indicate present speed within tolerances.

tAc: Displays the tachometer data received from the PCM via the SCP network within tolerances. Tachometer will indicate present RPM.

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

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