P0579-SPEED CONTROL SWITCH 1 PERFORMANCEFor a complete wiring diagram Refer to Section 8W.When Monitored:With the ignition key on.Set Condition:Cruise switch voltage output is not out of range but it does not equal any of the values for any of the button positions. One trip fault.
Possible Causes(V71) S/C SIGNAL 1 CIRCUIT SHORTED TO BATTERY VOLTAGE(V71) S/C SIGNAL 1 CIRCUIT OPEN(V937) S/C RETURN CIRCUIT OPEN(V71) S/C SIGNAL 1 CIRCUIT SHORTED TO GROUND(V71) S/C SIGNAL 1 CIRCUIT SHORTED TO THE (V937) S/C RETURN CIRCUITSPEED CONTROL SWITCHPCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).Diagnostic Test1.SPEED CONTROL SWITCH STATUSStart the engine.With a scan tool, monitor each which function for the Speed Control Switch.Notice the voltage reading when no buttons are pressed.Press and release each Speed Control Button.- Resume/Accel- Cancel- Decel (Coast)- On/Off- SetDoes each switch function change status when pressing and then depressing each switch?YesRefer to the INTERMITTENT CONDITION Diagnostic Procedure.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)NoGo To 22.SPEED CONTROL SWITCHTurn the ignition off.Remove and disconnect the Speed Control Switch from the steering wheel per Service Information.Measure the resistance across each Speed Control Switch.Monitor the ohmmeter while pressing each function button on the switch.The following resistance specs are taken between terminals (V71) S/C Signal 1 and (V937) S/C Return circuit of the Switch when holding the switch button in the following positionNot pressing any switch - 20.5 kohmsOn/Off - 0.47 kohmsSet - 5.49 kohmsCoast - 2.94 kohmsCancel - 1.24 kohmsResume/Accel - 15.4 kohmsDoes the function on the Speed Control Switches have the correct resistance value?YesGo To 3NoReplace the Speed Control Switch that had the incorrect resistance value.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)3.(V71) S/C SIGNAL 1 CIRCUIT SHORTED TO BATTERY VOLTAGEDisconnect the C3 PCM harness connector.Ignition on, engine not running.Measure the voltage on the (V71) S/C Signal 1 circuit in the S/C Switch harness connector.Is the voltage above 0 volts?YesRepair the short to battery voltage in the (V71) S/C Signal 1 circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)NoGo To 44.(V71) S/C SIGNAL 1 CIRCUIT OPENDo not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special
Tool #8815 to perform diagnosis.Turn the ignition off.Measure the resistance of the (V71) S/C Signal 1 circuit from the Speed Control Switch to the appropriate terminal of special tool #8815.Is the resistance below 5.0 ohms for each measurement?YesGo To 5NoRepair the open in the (V71) S/C Signal 1 circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)5.(V937) S/C RETURN CIRCUIT OPENDo not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special
Tool #8815 to perform diagnosis.Measure the resistance of the (V937) S/C Return circuit from the S/C Switch harness connector to the appropriate terminals of special tool #8815.Is the resistance below 5.0 ohms for each measurement?YesGo To 6NoRepair the open in the (V937) S/C Return circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)6.(V71) S/C SIGNAL 1 CIRCUIT SHORTED TO GROUNDMeasure the resistance between ground and the (V71) S/C Signal 1 circuit in the S/C Switch harness connector.Is the resistance below 100 ohms?YesRepair the short to ground in the (V71) S/C Signal 1 circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)NoGo To 77.(V71) S/C SIGNAL 1 CIRCUIT SHORTED TO THE (V937) S/C RETURN CIRCUITMeasure the resistance between the (V71) S/C Signal 1 circuit and the (V937) S/C Return circuit in the S/C Switch harness connector.Is the resistance below 5.0 ohms?YesRepair the short between the (V71) S/C Signal 1 circuit and the (V937) S/C Return circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)NoGo To 88.SPEED CONTROL SWITCH VOLTAGE VALUESAllow the engine to idle.With a scan tool, monitor the S/C Switch voltage readings.
SWITCH POSITIONSWITCH No.1 VOLTAGE VALUESWITCH No.2 VOLTAGE VALUENO SWITCHES PRESSED 4.31 to 4.78 volts4.31 to 4.78 voltsON/OFF PRESSED0.59 to 1.13 volts3.53 to 3.92 voltsRES/ACCEL PRESSED3.88 to 4.17 volts2.04 to 2.47 voltsSET PRESSED3.16 to 3.56 volts1.17 to 1.56 voltsCOAST PRESSED2.57 to 2.94 volts0.77 to 1.09 voltsCANCEL PRESSED1.59 to 1.99 volts2.84 to 3.25 volts
Take these same voltage measurements with a voltmeter by back probing the (V71) S/C Signal 1 circuit and the (V72) S/C Signal 2 circuit at the switches.Compare the voltage readings on the voltmeter to what the scan tool displayed.Are the voltage readings out of the listed specification and is there less than a 0.2 of a volt difference between the voltmeter switch values and the scan tool switch value?YesReplace the Speed Control Switch.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)NoGo To 99.PCMBefore continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.Were there any problems found?YesRepair as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)NoReplace and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)