P1593-SPEED CONTROL SWITCH 1/2 STUCK





For a complete wiring diagram Refer to Section 8W.



Possible Causes
S/C SWITCH SIGNAL CIRCUITS SHORTED TO BATTERY VOLTAGE
RESISTANCE IN THE S/C SWITCH SIGNAL CIRCUITS
RESISTANCE IN THE (V937) S/C RETURN CIRCUIT
S/C SWITCH SIGNAL CIRCUITS SHORTED TO THE (V937) S/C RETURN CIRCUIT
(V71) S/C SIGNAL 1 CIRCUIT SHORTED TO THE (V72) S/C SIGNAL 2 CIRCUIT
S/C SWITCH SIGNAL CIRCUITS SHORTED TO GROUND
SPEED CONTROL SWITCH
PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).



Diagnostic Test

1. ACTIVE DTC

Ignition on, engine not running.

NOTE: This DTC is a two trip fault. If the scan tool indicates a one trip failure, the possible cause may have been the customer pressing the switch in two positions simultaneously. Test drive the vehicle and activate the Speed Control system. If the DTC matures to an active fault a repair is necessary.


Ask the customer if it is possible that button was held in two positions at the same time before this DTC set. If this is the case, no repair is necessary.
Start the engine.
Allow the engine to reach normal operating temperature.
With a scan tool, select View DTCs.

NOTE: It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.



Is the DTC Active or Pending at this time?

Yes


No

2. SPEED CONTROL SWITCH

With the scan tool, monitor the Speed Control Switch voltage.
Disconnect the Speed Control Switch harness connector.

Did the voltage change to above 4.8 volts?

Yes


No

3. SPEED CONTROL SWITCHES

Turn 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 each switch.
The following resistance specs are taken between terminals (V72) S/C Signal 2 and (V937) S/C Return circuits of the Switch when holding the switch button in the following position.
Not pressing any switch - 20.5 kohms
On/Off - 8.87 kohms
Set - 0.825 kohms
Coast - 0.47 kohms
Cancel - 3.92 kohms
Resume/Accel - 1.87 kohms
The following resistance specs are taken between terminals (V71) S/C Signal 1 and (V937) S/C Return circuits of the Switch when holding the switch button in the following position
Not pressing any switch - 20.5 kohms
On/Off - 0.47 kohms
Set - 5.49 kohms
Coast - 2.94 kohms
Cancel - 1.24 kohms
Resume/Accel - 15.4 kohms

Does the function on the Speed Control Switch have the correct resistance value?

Yes


No

4. S/C SWITCH SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE





Disconnect the C3 PCM harness connector.
Measure the voltage on the (V71) and (V72) S/C Signal circuits at the Speed Control harness connector.

Is the voltage above 5.0 volts?

Yes


No

5. S/C SWITCH SIGNAL CIRCUIT OPEN




CAUTION: Do 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 (V71) and (V72) S/C Signal circuits from both Speed Control harness connector to the appropriate terminals of special tool #8815.

Is the resistance below 5.0 ohms for each measurement?

Yes


No

6. (V937) SWITCH RETURN CIRCUIT OPEN


NOTE: The measurement must be taken from both Speed Control Switch harness connectors.


Measure the resistance of the (V937) S/C Return circuit at the Speed Control harness connector to the appropriate terminal of special tool #8815.

Is the resistance below 5.0 ohms for both measurements?

Yes


No

7. S/C SWITCH SIGNAL CIRCUITS SHORTED TO THE (V937) S/C RETURN CIRCUIT





Measure the resistance between the (V937) S/C Return circuit and both of the (V71) and (V72) S/C Signal circuits in the S/C Switch harness connector.

Is the resistance below 5.0 ohms?

Yes


No

8. (V71) S/C SIGNAL 1 CIRCUIT SHORTED TO THE (V72) S/C SIGNAL 2 CIRCUIT



Measure the resistance between the (V71) S/C Signal 1 circuit and the (V72) S/C Signal 2 circuit at the Speed Control harness connector.

Is the resistance below 100 ohms for each circuit?

Yes


No

9. S/C SWITCH SIGNAL CIRCUITS SHORTED TO GROUND





Measure the resistance between ground and the (V71) and (V72) S/C Switch Signal circuits at both S/C Switch harness connectors.

Is the resistance below 100 ohms?

Yes


No

10. SPEED CONTROL SWITCH VOLTAGE VALUES

Allow the engine to idle.
With a scan tool, monitor the S/C Switch voltage readings.

SWITCH POSITION
SWITCH No.1 VOLTAGE VALUE
SWITCH No.2 VOLTAGE VALUE
NO SWITCHES PRESSED
4.31 to 4.78 volts
 		4.31 to 4.78 volts
ON/OFF PRESSED
 		0.59 to 1.13 volts
 		3.53 to 3.92 volts
RES/ACCEL PRESSED
 		3.88 to 4.17 volts
 		2.04 to 2.47 volts
SET PRESSED
 		3.16 to 3.56 volts
 		1.17 to 1.56 volts
COAST PRESSED
 		2.57 to 2.94 volts
 		0.77 to 1.09 volts
CANCEL PRESSED
 		1.59 to 1.99 volts
 		2.84 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 switch.
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 values?

Yes


No

11. PCM

NOTE: Before 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?

Yes


No