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DTC P1596: Speed Control Switch Always High

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION  . For wiring diagram, see WIRING DIAGRAMS article.
NOTE: Speed control switch is monitored when ignition is on. DTC may be stored in Powertrain Control Module (PCM) if open is detected in speed control on/off switch circuit and voltage is more than 4.8 volts for more than 2 minutes. Possible causes are: defective speed control on/off switch, defective PCM, or defective connectors or wiring.
  1. Start engine and allow engine to idle. Using scan tool in INPUTS/OUTPUTS mode, read speed control inputs. Monitor display on scan tool while turning speed control on/off switch on the steering wheel to ON and OFF positions several times with the switch returned to the ON position. If scan tool displays speed control on/off switch turns OFF and ON, go to next step. If scan tool does not display speed control on/off switch turns OFF and ON, go to step  3 .
  2. Shut engine off. Inspect wiring harness and connectors between speed control on/off switch, clockspring and PCM. Clockspring is located on steering column, below steering wheel. PCM is located at passenger's side front corner of engine compartment on inner fender panel. If necessary to check connector C200, this is a Black 42-pin connector located behind driver's side of instrument panel, near kick panel. See Fig 1 . If no problem exist, test is complete. If any problems exist, repair wiring or connectors as necessary. Perform TEST VER-4  .
    Fig 1: Locating Connector C200 & Clockspring Connector No. 1
    G00014897Courtesy of DAIMLERCHRYSLER CORPORATION
  3. Shut engine off. Ensure ignition is off. Disconnect speed control on/off switch 2-pin connector at rear of speed control on/off switch assembly. Disconnect clockspring connector No. 1. Clockspring connector No. 1 is a 5-pin connector located near steeering wheel. See Fig 1 . Using ohmmeter, check resistance between each wire in speed control on/off switch 2-pin connector at rear of speed control on/off switch and terminal No. 3 (Black/Light Blue wire) on clockspring connector No. 1. This is the ground circuit for speed control on/off switch. One of the wires in the speed control on/off switch 2-pin connector goes to terminal No. 3 (Black/Light Blue wire) on clockspring connector No. 1, as no wire color was available from manufacturer. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open on Black/Light Blue wire between clockspring connector No. 1 and speed control on/off switch. Perform TEST VER-4  .
  4. Ensure ignition is off and clockspring connector No. 1 is still disconnected. Disconnect PCM connectors. PCM is located at passenger's side front corner of engine compartment on inner fender panel. Using ohmmeter, check resistance between terminal No. 3 (Black/Light Blue wire) on clockspring connector No. 1 and terminal No. 4 (Black/Light Blue wire) on PCM connector C1. This is the ground circuit for speed control on/off switch. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open on Black/Light Blue wire between clockspring connector No. 1 and PCM. Perform TEST VER-4  .
  5. Ensure speed control on/off switch 2-pin connector at rear of speed control on/off switch assembly is still disconnected. Using ohmmeter, check resistance between electrical terminals on speed control on/off switch. If resistance is 20,300-20,700 ohms, go to next step. If resistance is not 20,300-20,700 ohms, replace speed control on/off switch. Perform TEST VER-4  .
  6. Ensure speed control on/off switch 2-pin connector at rear of speed control on/off switch assembly is still disconnected. Reinstall PCM connectors and clockspring connector No. 1. Turn ignition on with engine off. Using voltmeter, check for voltage at each wire in speed control on/off switch 2-pin connector at rear of speed control on/off switch to see if the switch signal is shorted to voltage. If voltage is 6 volts or less, go to next step. If voltage is more than 6 volts, repair short to voltage on Red/Light Green wire between PCM, clockspring and speed control on/off switch assembly. Perform TEST VER-4  .
  7. Turn ignition off. Disconnect PCM connectors and clockspring connector No. 1. Using ohmmeter, check resistance between terminal No. 1 (Red/Light Green wire) on clockspring connector No. 1 and terminal No. 32 (Red/Light Green wire) on PCM connector C3. This is the signal circuit for speed control on/off switch. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open on Red/Light Green wire between clockspring connector No. 1 and PCM. Perform TEST VER-4  .
  8. Ensure speed control on/off switch 2-pin connector at rear of speed control on/off switch assembly and clockspring connector No. 1 is still disconnected. Using ohmmeter, check resistance between each wire in speed control on/off switch 2-pin connector at rear of speed control on/off switch and terminal No. 1 (Red/Light Green wire) on clockspring connector No. 1. This is the signal circuit for speed control on/off switch. One of the wires in the speed control on/off switch 2-pin connector goes to terminal No. 1 (Red/Light Green wire) on clockspring connector No. 1, as no wire color was available from manufacturer. If resistance is less than 5 ohms, replace PCM. Perform TEST VER-4  . If resistance is 5 ohms or more, repair open on Red/Light Green wire between clockspring connector No. 1 and speed control on/off switch. Perform TEST VER-4  .
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