Diagnostic Overview - S/C Switch

The fact that the PCM uses a common signal and sensor ground to detect several switch positions helps in determining if a fault is most likely due to a switch or wiring issue. Checking the voltage readings while cycling through the different S/C Switch positions can be an easy way to determine this. The voltage readings can be monitored using the scan tool or by back probing and measuring each signal circuit voltage with a voltmeter and comparing them to the specifications in the table. Read and record the voltages for both signals with the switch not pressed and then while pressing each switch position. Using the voltage reads for both S/C Signals, use the information below to determine the most likely failure possibility:

• If one signal input voltage read is 5.0 volts when at rest and all other S/C Switch positions, the most likely cause is either the signal circuit is open or the switch is faulty.
• If both signal input voltage reads are 5.0 volts when at rest and all other S/C Switch positions, the most likely cause is the sensor ground circuit is open.
• If either signal input voltage read is 5.0 volts when at rest, but has a valid voltage signal during any of the other S/C Switch positions, the most likely cause is a faulty switch.
• If either signal input voltage read is 0.0 volts, the most likely cause is the signal circuit shorted to ground.
• If one signal input voltage read is outside of the normal operating range for all S/C Switch positions, the most likely cause is excessive resistance in the signal circuit.
• If both signal input voltage reads are outside of the normal operating range for all S/C Switch positions, the most likely cause is excessive resistance in the sensor ground circuit.

The failures described above are to help shortcut and eliminate causes that are unlikely based on the voltage reads. The circuits and MUX Switch should still be checked and confirmed faulty before any repairs are made.