Without Scan Tool

Fig. 19 Reading codes using analog voltmeter:

When a service code is reported on the analog voltmeter for a function test, it will represent itself as a pulsing or sweeping movement of the voltmeters needle across the dial face of the voltmeter. A single digit number of three will be represented by three needle pulses (sweeps), Fig. 19.
As previously stated, a service code is sometimes represented by a two digit number, such as 23. As a result, the self-test service code of 23 will appear on the voltmeter as two needle pulses (sweeps) then, after an approximately 1.6 second pause, the needle will pulse (sweep) three times. The continuous memory codes are not separated from the Key-On/Engine-Off codes. They are produced on the voltmeter in the same manner as the Key-On/Engine-Off codes.