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DTC Test 32: Cruise Control Switch Circuit

WARNING: This page is about a different car, the 1997 Lexus SC 400. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check if cruise control ECU is receiving input signals from control switch. See INPUT SIGNAL CIRCUITS  under CIRCUIT TESTS. If input signal circuits are not okay, go to next step. If input signal circuits are okay:
    • CODE - Check for intermittent condition (poor connections, etc.). If connections are okay, replace cruise control ECU.
    • NO CODE - Perform next procedure listed in DIAGNOSIS BY SYMPTOM  table in TROUBLE SHOOTING.
  2. Remove cruise control ECU, leaving electrical connector(s) attached. Turn ignition on. Measure voltage between ground and terminal No. 18 of cruise control ECU connector. See CONTROL SWITCH INPUT VOLTAGE  table. See Fig 1. If voltage is not as specified, go to next step. If voltage is as specified:
    • CODE - Check for intermittent condition (poor connections, etc.). If connections are okay, replace cruise control ECU.
    • NO CODE - Perform next procedure listed in DIAGNOSIS BY SYMPTOM  table in TROUBLE SHOOTING.
      WARNING: To avoid accidental air bag deployment, see AIR BAG RESTRAINT SYSTEM article before removing or installing steering wheel pad.
  3. Remove steering wheel pad. See AIR BAG RESTRAINT SYSTEM article. Disconnect electrical connector from cruise control switch. Check resistance between terminals No. 3 and 4. See Fig 1. See CRUISE CONTROL SWITCH RESISTANCE  table.
  4. If resistance is not as specified, replace cruise control switch. If resistance is as specified, check wiring harness and connectors for loose connections. Repair wiring harness and connectors as necessary. If wiring harness and connectors are okay, replace cruise control ECU.
CONTROL SWITCH INPUT VOLTAGE

Application Volts
Neutral Position 10-14
RESUME/ACC Position 0.8-3.6
SET/COAST Position 2.5-6.2
CANCEL Position 4.2-8.7
CRUISE CONTROL SWITCH RESISTANCE

Application Ohms
Neutral Position (1) At Least 1 Megohm (Infinite)
RESUME/ACC Position 60-80
SET/COAST Position 180-220
CANCEL Position 400-440
(1) Resistance that is less than infinite may cause Code 34 to set. Carefully ensure resistance is infinite, especially when switching between RES/ACC and SET/COAST positions.
Fig 1: Identifying Cruise Control Switch Terminals
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