Code 24, VSS "A Body" W/ Standard Instruments
The ECM supplies a current limited 12 volt signal on circuit 437. The Vehicle Speed Sensor (VSS) will sense the speedometer rotating element and furnish this information to the buffer as a "Pulsed" signal, 2 pulses per cable revolution or 2002 per mile. The buffer assembly will switch circuit 437 to ground for each pulse received. The ECM uses the time between pulses to determine vehicle speed. Code 24 is set by the following:
- ECM receives no VSS signal.
- Engine speed is more than 1800 RPM ("E" and "G" series 1400 RPM).
- Park/Neutral switch indicates transmission is in Drive range.
- For at least 25 seconds ("E" and "G" series 20 seconds).
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- This test checks if there is a VSS signal to the ECM while turning drive wheel. Voltage should vary from less than 4 volts to more than 6 volts with less variation as wheel speed increases. ("A" series with standard cluster 4-8 volts.)
- This test checks ECM and wiring harness to VSS buffer (I.P. cluster on "A" series with standard cluster.)
- This test checks if ECM recognizes the VSS signal.